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Sustainability and Affordability:How Single-Family Home Retrofits Can Achieve Both
Jason Goff
Mentor: Colby Moeller
Fall 2015
SBE 498
Table of Contents
Abstract....................................................................................................................................................................... 1
Introduction.................................................................................................................................................................2
Methodology...............................................................................................................................................................3
Literature Review.........................................................................................................................................................4
Sustainability and the Built Environment.....................................................................................................................5
The Modern Foundation for Sustainability..............................................................................................................6
The Three Pillars and the Built Environment...........................................................................................................6
Buildings and the Environment................................................................................................................................7
Energy and Pollution...........................................................................................................................................7
Water..................................................................................................................................................................9
Building Materials, Waste, and Disposal...........................................................................................................11
Land Use............................................................................................................................................................12
Buildings and Society.........................................................................................................................................14
Buildings and Economics...................................................................................................................................16
The Modern (Re)Built Environment.......................................................................................................................17
New vs. Retrofit.................................................................................................................................................20
Retrofit Precedent.............................................................................................................................................21
Data & Discussion......................................................................................................................................................22
Sustainability and Affordability in Southern Arizona.............................................................................................22
Case Study: The Tucson House..............................................................................................................................25
Assets................................................................................................................................................................26
Deficiencies.......................................................................................................................................................27
The Base Case Retrofit...........................................................................................................................................28
The Retrofit+Addition............................................................................................................................................34
Cost........................................................................................................................................................................36
Results.......................................................................................................................................................................37
Conclusions............................................................................................................................................................41
Limitations.........................................................................................................................................................42
Recommendations.................................................................................................................................................43
Appendix....................................................................................................................................................................... i
Bibliography................................................................................................................................................................ iii
Figure 1. Water Use source: http://water.usgs.gov/watuse/wuto.html...................10Figure 2: Heat Island Effect........................................................................................................................13Figure 3: Health and Socioeconomic Status...............................................................................................15Figure 4. Green Home Listings in Tucson, Basic Characteristics.................................................................23Figure 5. Green Home Listings in Tucson: Cost and Availability.................................................................24Figure 6. Mortgage Calculator Results......................................................................................................24Figure 7. Affordable Home Price on a Median Income..............................................................................25Figure 8. Tucson Green Housing Affordability...........................................................................................25Figure 9. Base Case House: Facing South...................................................................................................26Figure 10. Climate Consultant 6: Psychrometric Chart..............................................................................29Figure 11. Climate Consultant 6: Design Guidelines Chart.........................................................................30Figure 12. Base Case ResCheck Compliance Graphic.................................................................................30Figure 13. Individual Strategy Comparisons..............................................................................................31Figure 14. Base Case Retrofit Floorplans...................................................................................................33Figure 15. Retrofit ResCheck Compliance Graphic.....................................................................................34Figure 16. Rendering of the Retrofit+Addition..........................................................................................35Figure 17. The Retrofit+Addition Floor Plans.............................................................................................36Figure 18. Retrofit+Addition ResCheck Compliance Graphic.....................................................................37Figure 19. Construction Costs....................................................................................................................37Figure 20. Base Case vs. Retrofit Annual Energy Use.................................................................................38Figure 21. Base Case vs. Retrofit Annual Electricity Use............................................................................39Figure 22. Solar-Estimator Graphic............................................................................................................40Figure 23. Base Case vs. Retrofit Utilities Use & Cost Comparison............................................................41Figure 24. Base Case vs. Retrofit Annual Emissions Results.......................................................................42Figure 25. Retrofit+Addition Annual Energy Use.....................................................................................42Figure 26. Side-by-Side Utilities & Cost Comparison - All Three Case Studies...........................................44Figure 27. Retrofit+Addition Emissions Results.........................................................................................44Figure 28. Retrofit+Addition Rendering.....................................................................................................45Figure 29. Summary of Results..................................................................................................................45Figure 30. Green Housing Affordability in Southern Arizona.....................................................................46Figure 31. Energy & Emissions: 3 Case Studies..........................................................................................47
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AbstractClimate change and resource availability are arguably the two biggest challenges
humanity faces going forward. An unprecedented body of scientific work has been compiled
over the past thirty years that indicates humans have and continue to be the largest driver of
these environmental concerns, and therefore must also be responsible for any solutions.
Buildings and their construction account for nearly 40% of the total energy consumption and
greenhouse gas emissions in the United States. Water consumption by both buildings and
thermoelectric power generation is also an issue, especially in the Southwest and Western
United States. Green building has been gaining steam in the U.S. for the past two decades, but
the primary focus has been in the commercial and industrial sectors. The residential markets
have not seen the efficiency gains, primarily due to the perception that the cost isn’t worth the
benefit.
This project examines the need, feasibility, and potential benefits of sustainably
retrofitting existing homes as an alternative to new construction. It provides a broad definition
of sustainability and then focuses into a more narrow description of its application within the
built environment. Using precedents, 3D modeling, and energy simulation software it
compares the energy and water savings of a retrofit versus a base case as well as the
performance of the average Southern Arizona home. Finally, this capstone project provides a
professional cost estimate for the implementation of the proposed changes and a side-by-side
look at the available “green” housing market, the utility cost savings for the homeowner, and
the environmental benefits of individual as well as large-scale adoption of sustainable
retrofitting practices.
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IntroductionThe global scientific community has become increasingly certain that human actions are
having a direct impact on our planet’s climate (Garfin, 2014). As the global population
continues to grow concerns are also being raised over human consumption exceeding the
earth’s carrying capacity (Pengra, 2012). As a result, in recent years, the concept of
sustainability has become more of a mainstream topic. How to consume less power and
produce more renewable energy, the quality and availability of freshwater sources, and
resource conservation and reuse have all become higher priorities.
Multiple points of attack for these problems have been identified, however a few of
these show greater promise for having a larger, faster, and longer lasting impact than the rest.
One area of focus is the built environment. According to the United Nations Energy Programme
website, “Buildings use about 40% of global energy, 25% of global water, 40% of global
resources, and they emit approximately 1/3 of greenhouse gas (GHG) emissions.” (Sustainable
Buildings and Climate Initiative, n.d.) In the U.S. buildings consume approximately the same
amount of energy, but domestically account for over 70% of electricity usage and produce
nearly 40% of the total GHG emissions (Buildings and their Impact on the Environment: A
Statistical Summary, 2009).
Beyond the environmental implications of a changing climate and a growing population,
discussion surrounding sustainability has developed to include social and economic principles.
The Three Pillars of Sustainability, or the triple bottom line as it is sometimes described, asserts
that for true sustainability to be achieved environmental, economic, and social factors must all
be relatively balanced. Balancing the principles makes sense, as adverse environmental
consequences are sure to impact economies and societies, but at the same time if a solution to
an environmental problem is socially unjust, or economically unsustainable, then it is unlikely to
succeed.
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Arizona and the Southwest present a unique opportunity to take a look at the built
environment and its current interaction with the three factors, and what we have to gain by
becoming more sustainable.
The 3rd U.S. National Climate Assessment describes the challenges facing this region:
The Southwest is the hottest and driest region in the United States, where the
availability of water has defined its landscapes, history of human settlement, and
modern economy. Climate changes pose challenges for an already parched
region that is expected to get hotter and, in its southern half, significantly drier.
Increased heat and changes to rain and snowpack will send ripple effects
throughout the region’s critical agriculture sector, affecting the lives and
economies of 56 million people – a population that is expected to increase 68%
by 2050, to 94 million. Severe and sustained drought will stress water sources,
already over-utilized in many areas, forcing increasing competition among
farmers, energy producers, urban dwellers, and plant and animal life for the
region’s most precious resource. (Garfin, 2014)
The report goes on to cite sea level rise, human health impacts, agricultural productivity, loss of
species diversity, and disrupted economies as the other significant casualties of climate change
in this region if nothing changes.
This capstone will examine one potential piece of the change necessary to avoid these
catastrophes. Its goal is to demonstrate that a well thought out sustainable retrofit of an
existing home is economically feasible, will make sustainable living more accessible to a larger
segment of society, and have a significantly positive impact on the environment.
MethodologyThis project will use primarily quantitative analyses to evaluate how well or poorly the
average home and the average existing “sustainable” home in Tucson performs using the triple
bottom line as a metric. However, certain categories of evaluation, such as land use and house
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size, are more subjective and require that a qualitative standard be established. Is a net zero
house that is 4,000 square feet still sustainable? Is a green home that requires clearing pristine
desert to build sustainable? For the purposes of this study, less is more or, “The most
sustainable building is the one that isn’t built” ( (Roberts, 2007).
Using this data to establish a baseline for improvement, I will then study the feasibility
of retrofitting a run-of-the-mill slump block home in Tucson to perform better in all three
categories of the triple bottom line. Utility bills, computer energy analysis, and a 3D digital
model of the existing structure will provide the base case, and each sustainability upgrade will
be quantitatively analyzed in terms of performance and cost, and documented in the model.
In addition to the upgraded base case, a second model that includes an addition of a
bedroom and bathroom, adding approximately 500 square feet to the original footprint will be
included. This will serve to make for a more equal comparison with the current sustainable
home offerings, as their square footages are typically larger than older homes. Qualitatively it
will also represent a finished product that is more in line with the current home buying trends
in the U.S., and hopefully suggest that affordable sustainable home ownership can be more of a
lateral move rather than a sacrifice of space or comfort.
Literature ReviewUltimately this paper argues that redesigning and redeveloping existing housing to
sustainable efficiency standards is not only feasible, but better at achieving the economic,
social, and environmental balance needed in the face of climate change and growing
populations than current new home design and construction standards, including most so-
called green or sustainable homes. The purpose of this literature review will be to provide a
modern definition of sustainability and explain the immediate need for its adoption; explain
how sustainability is related to the built environment; and to examine studies and precedents
of sustainable retrofitting and compare them to current building practices and costs.
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Sustainability and the Built EnvironmentThe UN Environment Programme’s report, Buildings and Climate Change: Summary for
Decision Makers, released ahead of the Copenhagen 2015 conference laid out six key points:
1. The building sector has the most potential for delivering significant and cost-effective
GHG emission reductions.
2. Countries will not meet emission reduction targets without supporting energy
efficiency gains in the building sector.
3. Proven policies, technologies and knowledge already exist to deliver deep cuts in
building related GHG emissions.
4. The building industry is committed to action and in many countries is already playing
a leading role.
5. Significant co-benefits including employment will be created by policies that
encourage energy efficient and low-emission building activity.
6. Failure to encourage energy-efficiency and low-carbon when building new or
retrofitting will lock countries into the disadvantages of poor performing buildings for
decades. (Huovila, et al., 2009)
This section of the literature review looks at the relationship between sustainability and
buildings in terms of the environment, society, and economics and will provide the foundation
for the argument that sustainable retrofits can address the six points above as well or better
than current building practices.
6
The Modern Foundation for SustainabilityIn 1984 the World Commission on Environment and Development (WCED), formed at
the request of the United Nations, set out to examine issues of the environment and
development, as well propose solutions. In 1987 the WCED (also known as the Brundtland
Commission after its chairman) released the Brundtland Report, titled “Our Common Future”. It
was not groundbreaking in the sense that the issues they highlighted were unheard of, but
there were four key elements that represented a change in attitudes and thinking and have
continued to shape the discussion on humanity and its interaction with the environment and
each other. The first major change was that the 21 nations involved with the report were able
to come to a consensus, not just on identifying the problems, but also on leveling responsibility
and proposing solutions. The second thing the Brundtland Report did was permanently link the
environment with development: "...the "environment" is where we live; and "development" is
what we all do in attempting to improve our lot within that abode. The two are inseparable."
(Brundtland, 1987). No longer could the natural world we live in exist as a separate entity from
the environment we create. The third thing the report gave us was a modern definition of
sustainable development: “Sustainable development is development that meets the needs of
the present without compromising the ability of future generations to meet their own needs”
(Brundtland, 1987). Finally, and perhaps their most important point of agreement, the
Brundtland Commission clearly laid out the connection between environmental health, social
justice, and economic prosperity. The three are interdependent, and a sustainable future
requires good stewardship of all three (Brundtland, 1987).
The Three Pillars and the Built EnvironmentThe built environment, although just one of many pieces of the global sustainability
puzzle, has a disproportionately large effect on all three pillars of sustainability. Land use and
resource consumption (environment), affordability and availability (social), and material and
labor costs as well as market fluctuations (economic) are just some of the many interrelated
factors that can work for or against the successful implementation of sustainable buildings.
With so many challenges to solve it is reasonable to ask the questions: Are we really living that
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unsustainably? Is sustainability worth the headache? What risks do maintaining the status quo
present? The following review of reports, statistics, and scientific projections will answer these
questions, and provide the opportunity to reframe them.
The United Nations’ Intergovernmental Panel on Climate Change (IPCC), created in
response to the Brundtland Report, has been analyzing and reviewing thousands of scientific
papers and reports from across the globe since 1988. A series of five summary reports, the first
in 1990 and the latest in 2014, have all been publicly released and are the basis for ongoing
international discussions on the causes, the immediate and projected impacts, and solutions to
the human contribution to climate change. With each report the degree of certainty that man-
made factors have contributed to climate change has increased, with the latest report stating
“with 95 percent certainty that human activity is the dominant cause of observed warming
since the mid-20th century.” (Climate Change 2013: The Physical Science Basis) The consensus
is that human activities have contributed to a 70% increase in global greenhouse gas (GHG)
emissions since the 1970s.
The next three sections will examine in more detail the interaction between the built
environment and society, the economy, and the natural world. While some impacts are specific
to one pillar of sustainability, it is important to remember that all three categories are
interrelated. What affects one also has consequences for the other two.
Buildings and the Environment
Energy and PollutionThe U.S. represents around 4.5% of the world’s population, yet energy consumption by
buildings alone in the U.S. accounted for 7% of total global energy use (U.S. Dep't of Energy,
2012). Three quarters of the energy consumed by U.S. buildings is produced by fossil fuels, and
84.5% of our total GHG production is energy related (EPA, 2015). Methane emissions attributed
to building energy consumption totaled an equivalent to 176 million metric tons of C02
(measurements of GHG emissions are typically standardized by converting to C02 equivalencies)
in 2009 and account for only 10% of our GHG production (EPA, 2015). However, according to
the Environmental Protection Agency (EPA), “Pound for pound, the comparative impact of CH4
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on climate change is 25 times greater than CO2 over a 100-year period.” This is an important
point, as methane releases will grow considerably as natural gas is the alternative of choice to
coal and government initiatives to reduce C02 emissions have made coal power less profitable
for energy companies. Electricity production accounts for 32% of the U.S.’s CO2 production, with
10% added from commercial and residential activities. Methane’s ties to energy lay primarily in
resource extraction, with nearly 40% of its atmospheric releases being tied to coal mining and
natural gas and petroleum systems (epa.gov).
While design changes in architecture, mechanical systems, and appliance technology
have improved building efficiencies by 30% over older building stock, population growth and
the subsequent need for more housing, increased home sizes, and the additional power
requirements of new personal technology (PCs, laptops, phones, etc.) have increased
residential energy consumption by 39%. (Center for Climate and Energy Solutions, 2015)
Air pollution and greenhouse gasses are often the focus of pollution discussions given
their contributions to climate change, however there are there are risks associated with the
built environment that should not be ignored. Material choices, whether in new construction or
retrofits, can pose a significant impact to human health. Off-gassing, also called out-gassing, is
the result of volatile organic compounds (VOCs) becoming gases at room temperature (AirData,
2015). The EPA warns that the concentration of these gases can contribute to eye, nose, and
throat irritation as well as the buildup of ground level ozone. Extended exposure to some VOCs,
like formaldehyde, have been found to cause cancer (Penafiel, 2006). Found in everything from
plywood and wood composites to paint and adhesives, VOCs are hard to avoid in any new
building project and extensive remodels, but there are low-VOC products on the market, and
several strategies minimize or eliminate the risk of human contact with them.
Materials and design choices can also affect our water supply both during construction
and occupancy. New site preparation generally involves considerable earth grading and moving,
potentially generating runoff sediments that find their way into streams, rivers, and other water
bodies that impact marine ecosystems. Roofing materials, concrete, pavement, paint, and even
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treated wood can release an array of heavy metals and organic compounds into water supply
through normal runoff (Clark, 2009).
WaterEnergy production and consumption and their attendant pollution are just one of the
many environmental impacts of buildings to be considered, however they go hand in hand with
water. Often the focus on the built environment is centered on improving energy efficiency,
however, the water cost of producing energy is not always equally discussed.
Water is used in every method of electricity generation we currently employ in the U.S
except for wind and solar. Water is also used in varying amounts during nearly every step of the
extraction and refining of fossil fuels, our primary energy source. Even “clean” energy like
biomass is exceptionally water intensive. Conversely, we use massive amounts of energy, by
one estimate 13% of our total national energy use, for water related energy uses (Bevan
Griffiths-Sattenspiel, 2009). Reciprocity between energy and water makes improving efficiencies
and decreasing consumption of both a key component of any discussion about sustainability.
The EPA estimates that if 1% of American homes were retrofitted with water-efficient fixtures
we would reduce GHG emissions by 80,000 tons and reduce electricity consumption by enough
to power 43,000 homes for a month (EPA U. , 2012).
The availability of freshwater, particularly in the West and Southwestern United States,
has been a major issue for decades, if not longer in some areas. The effects of climate change
have intensified the strain on this critical resource in these regions as evidenced by long term
extreme drought conditions, record and more regular heat waves, and longer and more
destructive wildfire seasons. The climate models don’t bear much good news for the southern
and western United States either. A 10-20% reduction of runoff from snowmelt is predicted
over the next 50 years; warmer temperatures will increase evaporation leading to less water
available for groundwater recharge; and earlier seasonal warming will affect the timing of river
and stream flows, affecting the water availability during traditionally peak use periods
(Georgakakos, 2014). Despite the visible and measurable evidence that water conservation
should be of the utmost importance, the U.S. continues consume more water per capita than
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any other nation (Fischetti, 2012). Globally irrigation accounts for over 70% of water use, yet
the USGS chart below shows the bulk of U.S. groundwater withdrawals is tied up in
thermoelectric power production.
Figure 1. Water Use source: http://water.usgs.gov/watuse/wuto.html
The average nationally is that it takes two gallons of water to produce one kilowatt hour
(kWh) of electricity, while nearly 4.5 gallons of water are needed in the Western region of the
U.S., and in Arizona it requires seven gallons. The differences are due to the varieties of energy
sources used. Arizona receives a significant portion of its power from hydroelectric, which
ironically is good for clean energy production, but poor (in a hot, arid climate) for evaporation.
Lake Powell and Lake Mead, both created by hydroelectric dams along the Colorado River, lose
an average of 2.3 billion gallons of water to evaporation each year compared to the natural
evaporation rate of the river (P. Torcellini, 2003). In a state where each household’s electricity
consumption averages 1000 KWh/month, 7 gal/kWh is significant.
Beyond the water embedded in our energy consumption, the average U.S. Household
uses around 80-100 gallons per day (gpd), according to the USGS website. Tucson is slightly
higher than the national average with 102 gpd, but is a leader in the Southwest when compared
to Phoenix at 123 gpd, or California at 360 gpd (or 170 gpd with outdoor watering restrictions in
effect). The USGS attributes 13.6% of our groundwater withdrawals to buildings (Water Use in
the United States, 2015). It is clear that improving power generation and irrigation water use
efficiencies are going to have the greatest effect in assuring our future freshwater supply, yet
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there are many things that designers, builders, and homeowners can do to reduce the
consumption in the building sector. According to the American Water Works Association a 30%
reduction in total water consumption by U.S. households could happen by simply switching to
water efficient fixtures, resulting in a daily savings of 5.4 billion gallon (Water Use Statistics,
2015).
Building Materials, Waste, and DisposalFrom 1900 to 2010 the U.S. consumption of raw materials, any resource other than fuel
or food, increased 2.8 times faster than the population grew. At its peak, just before the
financial collapse in 2006, three-quarters of that was used in construction, totaling nearly 3
billion metric tons of materials (Matos, 2012). Consumption dropped by 34% during the
recession, but is a trend that has already begun reversing as the demand for new construction
has begun to pick back up.
In 2013, the municipal solid waste (MSW) produced in the U.S. totaled 254.1 million
tons, with just over 34% being recovered through recycling and composting (Wastes - Non-
Hazardous Waste - Municipal Solid Waste, 2015). By comparison, the total construction and
demolition (C&D) waste for the same year was 162.2 million tons, with an estimated 20-30%
being recycled (EPA, 2015). Of that, approximately 50% was produced by buildings – roads,
infrastructure, and “other” account for the rest. A 2009 report by the EPA estimated that
residential construction in 2003 accounted for nearly 40 million tons of materials demolitions,
while renovations produced 19 million tons of waste. These numbers are expected increase,
with an estimate of 82 billion tons to be generated between 2005 and 2030 (Frey, 2011).
Economic fluctuations will produce year to year variation in these totals, but on average four
pounds of waste are generated per square foot of building, or between two and seven tons for
a new, median-sized single family home, and fifteen to seventy pounds of hazardous waste
(paint, caulking, aerosols, adhesives, etc.) are normal byproducts of new construction.
Not only does C&D waste present the issue of its disposal, it also represents enormous
quantities of embodied energy, and even higher life-cycle energy costs. Embodied energy is the
amount of energy it takes to create a product. A life-cycle assessment of materials factors in the
embodied energy as well as maintenance and eventual disposal of a product for its entire
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lifespan, also known as cradle to grave. This is a more accurate measure of a building’s
contributions to energy consumption, pollution, and overall cost than just looking at a materials
invoice and some utility bills.
Land UseAfter World War II there was a mass exodus from our city centers out to the new
suburbs. We were in a booming post-war economy and homes, cars, and fuel were affordable,
and those who had the means saw no problem with commuting. This was the beginning of
urban sprawl, and began a period of growth during which “Urban land acreage quadrupled
from 1945 to 2007, increasing at about twice the rate of population growth over this period.”
This represents a jump from around 15 million acres to over 60 million acres. (Cynthia
Robertson, 2011). Forty-one percent of that acreage was previously forest land, and fifty-two
percent of it was rural land previously used for agriculture. Several studies have found that
closer proximity to development increases the “…threat from pests, disease, pollution, and fire”
to forests as well as “…decrease management, investment, and harvest rates on private
forestlands.” (Cynthia Robertson, 2011)
In addition to forest and arable land loss, grasslands, wetlands, and desert have also
been impacted. Beyond the biodiversity loss and risks to ecosystems health caused by urban
expansion, the encroachment into forests, grasslands, and wetlands also represent reductions
of natural carbon sinks. Reductions to natural systems that regulate carbon just accelerate the
problem of climate change. Draining wetlands presents the added negative of methanogenesis,
or the process of methane being released when organic material is oxidized.
Fortunately land use is one area that is beginning to show signs of progress. The trend of
outward migration to the suburbs is reversing, with more and more people returning to urban
cores. This is good for land conservation efforts, but will present other challenges mostly out of
the scope of this paper. One area of consideration is ground cover. In dense urban city centers
and sprawling stretches of strip malls and neighborhoods devoid of the native trees they are
named after, the proliferation of asphalt, concrete, brick and the noticeable absence of natural
vegetation contribute to a couple of problems. This is called impervious ground cover, and it
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has a couple of consequences. The first is called the heat island effect, a phenomenon resulting
from the storage of solar energy in man-made materials throughout the day resulting in even
hotter days and, as anyone who has been in Phoenix at night during the summer, not much
cooler nights. This causes the temperature to remain higher than it would normally, which
means people are using air conditioning more, consuming more energy, thus producing more
GHGs, and the cycle just gets worse and worse.
Figure 2: Heat Island Effect
The second problem has to do with the effect of impervious ground cover on water
runoff. Precipitation cannot get through the asphalt and concrete that is spread across the
surface of the earth, which also means that the natural vegetation has been mostly if not
completely removed. This has the effect of altering water runoff and changing natural water
flows; it also affects water quality by delivering every pollutant, toxic contaminant, and fertilizer
that can be washed onto and off of these surfaces to the nearest watershed. These are
Source: nasa.gov
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problems that should be being tackled by city planners, but developers, builders, and
homeowners can also do much to minimize the impacts of single family homes by paying
attention to landscaping and material selection.
Buildings and SocietyThe built environment affects society everything from social mobility and human health
to our relationships with the natural environment and one another. Some of the observed
characteristics of homeowners include: a generally higher level of success in labor markets
compared to renters; better ability to maintain and improve property; more environmentally
conscious than non-homeowners; more politically and socially involved; improved mental and
physical health (Dietz, 2003). These social benefits are reinforced by the economic incentives
provided by federal, state, and local governments for homeownership. However these
opportunities have not, and arguably continue to not be, equitably distributed among the U.S.
population, particularly along racial lines.
Socioeconomic status and the opportunity for ownership has been studied extensively
for decades and the consensus is that housing discrimination has contributed to an ever
growing income gap with minority groups being disproportionately affected. One Harvard
University Law School study found that the median net worth of a homeowner in the U.S. was
$171,000, while that of a renter was only $4,800 (Webb-Williams, 2006).
The relationship between socioeconomic status and health and life expectancy has also
been well documented, with a combination of physiological and psychological stresses reducing
the productivity and lifespans of those economically disadvantaged (Sapolsky, 2005)
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Figure 3: Health and Socioeconomic Status
The built environment also affects society in subtler ways. Professor Kaveh Samiei, an
architect and researcher at Penn State University, believes the built environment can create
either a connection or a disconnection between humans and the natural environment. Since
the industrial revolution and the advent of the modern city, he believes, humanity has become
increasingly separated from the natural world, much to our detriment:
Ecosystems provide our basic human and social needs. The biosphere nurtures our mind
and soul, as well as our stomachs and lungs. The modern city is organic process, but one
with an unhealthy bio system. The biophilia hypothesis suggests that humans have an
innate tendency to affiliate with other living organisms and living processes. Humans
Source: Scientific American
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require contact with a biodiverse world to stimulate the development of their
emotional, cognitive, and social potential. As the living community of other organisms is
reduced and human interaction with that community is lost, there is an extinction of
experience that results in a loss of real ecological knowledge and emotional attachment
to nature. (Samiei, 2013)
The population of a world facing a climate crisis cannot continue to be indifferent to
everything beyond the concrete and asphalt of their immediate surroundings. Humans seem to
have an innate ability to avoid being proactive, relying on intellect and technology to reactively
solve self-imposed crises. This may prove useful in adapting in the short-term, but a deeper
connection to our planet, understanding ourselves to be a part of a single ecosystem and
respecting it and caring for it as such, is the only way humanity is going to find the collective will
to adopt the sustainable principles necessary for us to avoid producing even greater climate
change and its consequences.
Buildings and Economics
To understand the impact of housing on our economy one only has to look as far back as
the most recent recession. Housing is as much a cornerstone of our economic system as it is the
American dream. It’s so important that it is federally subsidized – upwards of $121 billion in
2013 alone – through mortgage programs like Fanny Mae and Freddy Mack, and property tax
deductions, and capital gains tax exclusions (Harris, 2013). Yet even as the government props
up the housing market in the interest of economic stability, it ignores a windfall of both public
and private benefits to be had by raising standards meaningful on design efficiency and build
quality, while at the same time incentivizing that environmental and social responsibility for
owners and developers.
It’s really simple math: healthier buildings mean a healthier, more productive society;
lower energy bills mean more money to be spent or invested in other segments of the
economy; a healthier environment benefits human health and reduces the costs of mitigating
environmental damage; sustainable design and construction requires new expertise,
technology, and innovation which creates new jobs in several sectors; and most importantly it
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reduces the burden on the generations to come. Unfortunately at this time federal and, in
many places, state funding for programs and incentives that promote green building and
retrofits is mostly nonexistent for residential construction.
The U.S. construction industry across all sectors - commercial, residential, industrial -
accounts for 5.5% of the total GDP in the U.S., and green projects have been steadily growing as
a share of the market, particularly in commercial and industrial applications. However, the
potential for the private home market is enormous. One study estimates the ten year potential
for residential retrofits alone could reach $400 billion, creating 280,000 jobs directly and over
660,000 indirectly (Pollin, 2009). The USGBC suggests there is far more money to be made,
stating “Current market trends suggest that building owners and managers will invest an
estimated $960 billion between now and 2023 on greening their existing built infrastructure.”
(USGBC, 2015)
The Modern (Re)Built Environment
This project’s aim is to prove that existing homes can be retrofitted to become
sustainable, which requires a definition of what exactly that means. Unfortunately a single,
concise, universally agreed upon definition for a sustainable building does not exist. So it’s no
surprise there are as many sets of sustainable building principles, rules, and fundamentals as
there are green building and third party certification programs that award recognition for
reaching sustainable goals that meet their specific definitions of what it means to be green.
Programs such as the EPA’s Energy Star and WaterSense target specific areas of efficiency and
conservation. The Energy Star program reviews, rates, and labels everything from light bulbs
and appliances to roof coatings and windows, providing consumers with at-a-glance energy
efficiency information. WaterSense applies the efficiency principles of Energy Star to plumbing
fixtures and water saving products.
Perhaps the most well-known green building certification is the U.S. Green Building
Council’s program, Leadership in Energy and Environmental Design (LEED), a points based
system that focuses on design efficiency, sustainable building practices, materials, building
performance, and occupant health. Some critics have pointed out that the points system can
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sometimes be gamed to achieve certification for buildings that do not perform well. Credits for
bicycle racks, limiting the number of parking spaces, LEED accredited team members (required
for the certification process anyway), and a handful of other low hanging fruit can gain buildings
accreditation while they fall short in other areas. Another criticism is that the certification
process can be completed prior to occupancy, so theoretical performance models and not
actual energy loads are used to determine whether or not a building receives achieves LEED
status.
Despite these drawbacks, due to its market-based approach and user input driven
revision process, the program has probably been the single greatest influence in the rise of
green building in the United States, and each new version of LEED that has been released has
become progressively more stringent. The Home Energy Rating System (HERS) is a system
developed by the Residential Energy Network (RESNET), a nonprofit founded in 1995 to help
owners improve their home’s efficiency and reduce utility bills. Using the U.S. Department of
Energy’s assessment that a typical resold home scores 130 on the HERS index and a newly
constructed home rates around 100, a baseline is given to begin applying and assessing
efficiency strategies. The lower the HERS number the better performing the home (RESNET,
2015). Another program, considered by many to be the most difficult to achieve certification in
is the Living Building Challenge. Certification requires that attention be paid to the
environmental, social, and economic aspects of sustainability and divides its focus among seven
“petals” that include Place, Energy, Water, Health & Happiness, Materials, Equity, and Beauty
which are further subdivided into twenty Imperatives. The end goal are buildings that more
reflect the natural environment in that they are net energy producers, designed with their
entire lifecycle in mind - including deconstruction, and promote symbiotic relationships
between the ecosystems and social networks they inhabit (Living Building Challenge, 2015).
Most of these add up to a lot of good intentions, and generally they do lead to buildings
with improved performance, but rarely do they produce a truly sustainable end result. In terms
of the IPCC’s definition of “development that meets the needs of the present without
compromising the ability of future generations to meet their own needs“ there are common
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principles among the certification programs that, when applied with the intention of achieving
a truly sustainable result instead of just a green label, sustainability can be achieved.
The first of these is to use integrated design principles. This means the entire building
has to be thought of as the sum of its parts and how well they interact with each other. This
requires a higher level of involvement from the owner, designer, builder, and the various
subcontractors that will be involved with a project. Together, before the project even begins,
they will establish the performance goals for the structure and collaborate on the most
effective and efficient strategies to achieve them. A well-integrated design will also consider the
life cycle of the building, as well as potential reuse or decommissioning possibilities.
The second common principle is to optimize energy performance. Typically energy
conservation efforts begin with a base case modeled off of the minimum performance required
by building code, then a target percentage for reducing energy consumption is set. A building’s
envelope – walls, windows, and roof – is generally where the most cost effective upgrades
occur. Insulating walls and the roof can offer substantial energy savings, while high
performance windows can be designed for specific climate needs and are crucial to a
structure’s energy performance, as inefficient windows can negate any gains upgraded
insulation provides. Another envelope consideration is shading. Blocking direct exposure to the
sun whether with trees or bushes or built shading structures can greatly improve building
envelope performance. The final piece of the envelope puzzle is how tight, or well-sealed, the
project is. This is particularly important in older existing buildings that can be quite drafty,
increasing the energy load to heat and cool the building.
The interior of a building offers energy saving potential in light fixtures, appliances, and
mechanical systems. Lighting can be minimized if effective daylighting strategies are used, such
as window placement, skylights, and interior walls and color palate that effectively allow
natural light to be distributed throughout the interior. The lighting that is required can take
advantage of high efficiency, low heat producing LED fixtures and bulbs. The Energy Star
website makes it easy to find and compare the top performing appliances on the market, and
energy efficient appliances can have a meaningful impact on utility bills. Energy Star also rates
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climate control systems, and along with a qualified HVAC technician, a properly sized heating
and cooling system integrated with a high performance building envelope can substantially
reduce the cost of achieving thermal comfort, especially in more extreme climates. If possible,
locating all ductwork within the conditioned space, rather than outside or in attic spaces, will
also improve HVAC efficiency. Finally, reducing plug loads from TVs, computers, stereos, small
appliances, and anything else that can be plugged into an outlet can offer more savings than
one might think. One study found that plug loads, even from devices that were “off”, drew 569
kWh in a year ( (Holladay, 2009). In some areas that equates to adding an extra month of
electricity consumption to an annual bill.
New vs. RetrofitIn from 2005 to 2011 the green building market grew from $10 billion to $78 billion, and
is projected to increase to more than $200 billion in 2016. The bulk of the growth has been
happening in the commercial and industrial sectors, however the residential market is expected
to have an 18% increase from 2012 to 2016, representing 20% of the market (McGraw-Hill:
Analytics, 2012).
With the U.S. population projected to grow by at least 100 million over the next 35
years, new housing is going to be necessary, and if construction trends stay constant it would
not be unreasonable to expect that 50% or more of new homes will be built green by 2050. This
is good news, but despite their sustainable labels there are carbon costs to new construction –
even in homes that have substantially improved energy performance – that are rarely
acknowledged. An in-depth study commissioned by the National Trust for Historic Preservation
found that “Building reuse almost always yields fewer environmental impacts than new
construction when comparing buildings of similar size and functionality.” The same report
found that residential retrofits with energy performance comparable to that of new green
construction had 15-17% reduction in climate change related impacts, and were 31-35% less
detrimental to their surrounding environments (Frey, 2011). They also discovered that new
structures built to be 30% more efficient than International Energy Conservation Code
standards, the minimum for a LEED for Homes certification, can take between 10 to 80 years to
offset the carbon emissions involved just in their construction. This strongly indicates that while
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new, green construction will be vital to providing housing and meeting our carbon-reduction
goals in the future, it will not immediately minimize construction related carbon emissions.
The extent to which we have to rely on new construction to meet our future housing
needs will depend on the degree of investment in building reuse and retrofitting we see going
forward. The 2015 Residential Vacancies and Homeownership 3rd quarter report released by the
Census estimated there are nearly 17.5 million vacant homes in the U.S., and 50% of the U.S.
residential building inventory was constructed before 1975. This represents easily 40 million
single-family homes nationwide that are potential deep-energy retrofit candidates, and there
are likely millions more built after 1975 that would benefit as well (Appendix, Table 1. American
Housing Survey).
Retrofit PrecedentThe ReVISION House in Las Vegas, Nevada is a 1960s “desert-modern” home designed
by William Krisel. Building Media, Inc. and Green Builder® Media, LLC collaborated with the U.S.
Department of Energy to perform a deep-energy retrofit that would reduce the home’s current
$500/month utility bills by 60% and then with the addition of PV solar bring the house to net-
zero energy consumption.
The 1,800 ft², single-story home has low-pitched roofs, wood framing, and lots of
windows. An energy audit found that old R-11 wall insulation that performed worse than the
wood studs, no roofing insulation, single-paned aluminum framed windows, unsealed
ductwork, inefficient HVAC and water heating units, incandescent lighting, and a drafty building
envelope contributed to abysmal energy performance.
The exterior stucco and sheathing was removed and spray foam was applied to the wall
cavity, then the house was re-sheathed and wrapped with weather barrier and an additional
layer of rigid foam exterior insulation panels before a new stucco finish and paint was applied
to the new R-21.5 walls. All the windows were replaced with triple-paned, fiberglass framed
Milgard windows. Eight inches of spray urethane insulation was also used to insulate and seal
the rafter bays of the roof, and an integrated air gap and venting system beneath the metal
standing seam BattenLok® cool roof created a system that exceeded an R-45 insulation value.
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All the mechanical systems were upgraded to high efficiency units, and the ductwork
was located within the conditioned space, mastic sealed, and insulated to R-8. Solar hot water
was added and connected in series with a new tankless water heater programmed to turn on
only if the preheated water was below a set temperature. Inside the house several fixtures
were upgraded to LEDs and the remaining fixture were upgraded with LED or CFL lightbulbs. A
whole house fan was installed to aid in ventilation, expelling warmer air and drawing healthy
fresh air into the much tighter sealed home.
In an effort to minimize the cost of the retrofit they attempted to do as much of the
work from the exterior of the house as possible, minimizing the amount of drywall repair and
refinishing required. In addition to the targeted upgrades, the plumbing was inspected and
replaced where necessary to avoid future pipe and fixture leakage, and some minor demolition
and reframing was performed to improve air circulation. The result of all these upgrades was a
home that began with a HERS Index score of 123 improving to a 44 before factoring in PV solar.
After solar was added the HERS rating improved to -2, effectively become a net zero home.
The estimated cost of the retrofit was $150,000 bringing the total cost of purchase and
improvements to $295,000 (Green Builder Media, 2010).
Data & Discussion
Sustainability and Affordability in Southern ArizonaWith the triple bottom line as a guide, searching the sustainable housing market in the
Tucson area leads only to one conclusion: there is very little true sustainable housing. The vast
majority of homes listed for sale as being “green” are either unaffordable or unsustainable. An
internet search for green/sustainable homes in Southern Arizona turned up a couple of
specialty websites and some individual listings from sites such as Zillow and Realtor.com. Sixty
homes from Tucson and surrounding areas were compiled into a database that took into
account location, age of construction, square footage, number of bedrooms and bathrooms,
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construction type, sustainable features, net zero performance, green certifications, and cost.
(Appendix, Table 2)
Size Bedrooms Baths Acreage Cost
Average 2,182 ft2 3 3 1.37 $344,709
Median 1,884 ft2 3 2.5 0.14 $257,900
After considerable searching, only five homes were listed for sale that could be
considered truly sustainable, even in just terms of their energy and water use, and their prices
ranged from $229,000 to $1.2 million. The two out of those five homes that were under
$300,000 were in rural locations. Figures 4 & 5 give some basic statistics for homes listed as
green or sustainable in the Tucson area.
Less than one third of the homes incorporated any onsite energy production, however
of the sixty surveyed 40% had solar hot water capabilities and around 65% were designed with
some type of water saving fixtures, greywater
plumbing, or rainwater harvesting systems. Less
than 10% were anywhere close to being net zero, and that number would have gone even
lower had the sample size been larger. More than 93% of the homes surveyed were new
construction. Less than 7% were retrofits. (Appendix, Table 2).
Category Price Availability
Median Listing Price of Net Zero Home $390,000 8.3%
Average Listing Price of Net Zero Home $579,200 of sampled listings
Median Listing Price of Home With PV $382,181 31.7%
Average Listing Price of Home With PV $289,000 of sampled listings
Average Listing Price of Green Remodel $631,750 6.7%
Median Listing Price of Green Remodel $524,000 of sampled listings
Figure 5. Green Home Listings in Tucson: Cost and Availability
Figure 4. Green Home Listings in Tucson, Basic Characteristics
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The three year average median income collected by the Census over the 2011-2013
period for Tucson was $49,774, with a standard error of $2,560. A 2011 Census report showed
median unsecured debt (credit cards, student loans, medical bills, small loans, etc.) was around
$7,000 (Vornovytskyy, Gottschalk, & Smith, 2011). The average annual property taxes in
Tucson are $1,524 and homeowners insurance averaged $540. So how much house can a
median income earner with good credit (a 3.85% APR was assumed) and a $10,000 down
payment?
U.S. Bank Zillow Bankrate Realtor.com CNN Money CreditKarma$0.00
$50,000.00
$100,000.00
$150,000.00
$200,000.00
$250,000.00
$300,000.00
Chart Title
10% Below Median Median 105 Above Mdian
Figure 6. Mortgage Calculator Results
The final affordable house prices were determined by entering the income, debt,
insurance, and property tax information into five different mortgage calculator programs and
taking the average (Appendix, Table 3). Obviously the debt, insurance, and tax categories are
subject to variation, so taking the Census estimated medians for each category seemed the
fairest starting point for determining affordability. In reality, the affordability on median income
would tend to be closer to the “10% below” numbers since unsecured debt doesn’t factor in
secured debt such as automobile loans, however for the purposes of this study I think the
ranges calculated below (Figure 7) are sufficient for determining the affordability of currently
available sustainable housing in southern Arizona, and whether or not sustainable retrofits offer
a cost effective alternative.
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Income
Annual Unsecured Debt (est.)
Annual Homeowners Insurance (est.)
AnnualProperty Taxes (est.)
Affordable House Price
10% Below Median $44,796 $7,000 $540 $1,524 $172,401Median $49,774 $7,000 $540 $1,524 $200,74010% Above Median $54,751 $7,000 $540 $1,524 $227,834
Figure 7. Affordable Home Price on a Median Income
The affordable price ranges in Figure 7 compared to the median costs of the sampled
listings, and the pie chart below (Figure 8) make it pretty clear that a large percentage of
sustainable homes are out of reach for those living on a median income, and there is potentially
a lot of money to be made in affordable green retrofitting if it can be proven to be cost
effective.
% of Tucson Green Homes Affordability on a Median Income
Median Income 10% Above Median10% Below Median Unaffordable on Median Income
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Case Study: The Tucson House
The home being studied for a sustainable retrofit is a three bedroom, one bath, 1,344 ft²
slump block home on 0.17 acres. It was built in 1954 and is approximately 5 miles east of
downtown Tucson. In 2013 the purchase price was $117,500 and other than landscaping the
backyard, the addition of a storage shed, and raising the height of the back privacy wall by two
feet with corrugated metal panels, no significant work has been done to it since being
purchased.
Assets
The house is oriented to the north and south, with a 30 degree turn to the East. There
are six windows and a sliding glass door, and all but two windows receive complete summer
shade. The roof is less than five years old, and has one layer of 2” rigid foam. The plumbing
pipes have been replaced, as has the water main. The back yard landscaping incorporates
native or drought tolerant species and earthwork that diverts and collect water. Half of the
house has upgraded electrical wiring and outlets. The home has a new 16-SEER split system
AC/furnace package and an 80% efficient hot water heater. A 30’ tall mesquite tree that
provides a substantial amount of shade for the west side of the house. The interior is for the
most part completely remodeled. The owners have some personal preference changes they
would like to make, but in general the house is move-in ready.
Figure 8. Tucson Green Housing Affordability
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Figure 9. Base Case House: Facing South
Deficiencies
The complete lack of insulation on the shell of this building is its biggest flaw. The south
facing wall of this home in particular is its weak spot, followed closely by its windows and roof.
The southern wall receives full sun except for the eastern third which is shaded by a patio
cover. Even that portion receives sun in the late afternoon when the sun drops low enough.
There is a completely unshaded 4’x4’ aluminum-framed window with low-e glass in the middle
of this wall. The performance of the low-e glass is handicapped due to the frame not being
thermally broken. The window on the west wall is shaded most of the day by the orientation of
the building and the mesquite tree but when the afternoon sun drops below the branches of
the tree the window receives direct sunlight for a couple of hours. The window is of the same
make and materials as the south window.
The roof has two deficiencies, the first also being insulation related. It has a single layer
of rigid foam, with an R-6 rating at best. The second is less the fault of the roof design as it is a
result of block walls, a messy mesquite tree, and the performance properties of cool roof
coatings. Much of the electrical wiring runs through conduits mounted across the roof. Code
calls for them to be raised so they do not accumulate debris and so potentially pooling water
cannot find its way into an improperly sealed conduit, but not everyone does things by the
book, especially on a house with 60 plus years of history. The mesquite tree which is fantastic
28
about shading the roof and the west side of the house for much of the day is also very messy,
dropping tiny leaves, pollen, and beans often and in large quantities throughout the year. This
detritus collects on the roof and if the homeowner is not diligent about cleaning it off piles will
form around the conduit. Any moisture that the roof receives will be absorbed into these piles
and begin to affect the composition of the roof coating, which is designed to shed water but
breaks down in standing water. A new roof was a mandatory component of the upgrade.
Also needing to be replaced is the electrical breaker panel. It currently is the code
minimum 100 amp service, noticeable whenever the A/C comes on and the interior lights dim.
In addition to the panel, the bedrooms in the house all need the wiring and outlets brought up
to code; only the kitchen, dining, living, and bathroom have updated wiring and grounded
outlets. In the living room ceiling are two of the cheapest polyacrylic and aluminum skylights
available. One has a hole in it and both will be replaced.
The rest of the windows in the house need to be replaced as well. All have thermally
unbroken aluminum frames which are great at conducting heat and cold, but not so good for
maintaining reasonable temperatures inside. Other areas that could use improvement are the
front yard landscaping, as it currently is the whole property slopes straight to the street. All of
the landscaping is native trees and cacti, but the potential to reshape the topography to collect
and direct water to more vegetation is there. Additional plants would decrease the reflected
heat of the mostly gravel landscaping, as well as gain some cooling benefits from the increased
evapotranspiration produced by more greenery. The backyard has been landscaped with native
and drought tolerant species, except for a small patch of grass. The newer plants still require
some watering, but have are sufficiently established so their watering needs has already gone
down. One of the criteria for upgrading the roof will be to implement rainwater collection
techniques, including the addition of gutters, directional downspouts, and cisterns.
This house also has zero graywater recycling capacities. At the minimum an under-the-
sink mounted tank and pump system will be installed to refill the toilet tank and, if it is not cost
prohibitive a tie-in to the shower drain that directs graywater to landscaping is also desirable. In
the case of the bathroom addition it will be plumbed for graywater. Finally, there has been no
29
attempt to harness the sun for electricity or hot water production. In a location that receives
over 300 days of sunshine per year this is a hugely missed opportunity.
The Base Case RetrofitIn addition to identifying the assets and deficiencies of the house through visual
assessment and interviewing the owners, Climate Consultant 6 (CC6) was used to determine
climate specific strategies for improving energy efficiencies. The psychrometric chart below,
generated by CC6, quantifies the degree to which specific strategies need to be implemented to
maintain thermal comfort in the Southern Arizona climate. A psychrometric chart uses wet bulb
and dry bulb temperatures to generate thermal comfort data for a specific climate. The chart
CC6 produced relies on a combination of shading, ventilation, passive solar gain, artificial
heating and cooling (HVAC), and user adaptation (i.e. season appropriate clothing, raising and
lowering the thermostat set points) to achieve 96.4% comfortable hours out of the total annual
hours of use.
30
Figure 10. Climate Consultant 6: Psychrometric Chart
The Climate Consultant Design Guidelines chart on the following page (Figure 10) lists
the top twenty suggested design strategies for the Southern Arizona climate. The green
highlighted guidelines are strategies that are absent from the base case and will be
implemented during the retrofit. The blue highlights indicate strategies that the base case
already incorporates and will be kept in addition to the retrofit. The pink indicates strategies
partially incorporated in the base case, but need further development. The red are guidelines
that are not incorporated at all in the base case, and are cost prohibitive to implement due to
the design of the existing structure. The strategies are listed in order of importance, the
numbers to the left are linked to more detailed information about each guideline.
Figure 11. Climate Consultant 6: Design Guidelines Chart
Using the CC6 recommendations and the known assets and deficiencies of the base case
home, 3D models of the base case, the Retrofit, and the Retrofit+Addition were created in
SketchUp to track design changes and model shading conditions. The construction materials of
31
the home were inspected, measured, and researched so they could be accurately accounted for
in the ResCheck and Energy-10 (E-10) energy modeling programs. ResCheck is the Department
of Energy’s program that allows a user to build a quick model based on size and material inputs,
and determine whether or not a building is energy code compliant for the area it’s going to be
built. It uses a simple U-factor x Area (UA) formula, and the base case was 21% higher than the
maximum allowable UA, which was to be expected.
Figure 12. Base Case ResCheck Compliance Graphic
The Energy-10 software allows precise values for walls, windows, roofing, flooring,
mechanical systems, and occupant loads as well as shading and solar orientation data to be
input. It produces a detailed and accurate prediction of building performance and uses the
building specs provided in the base case to create a Low-Energy Case with an array of efficiency
upgrades. The program assumes that structures are built new, resulting in Low-Energy Case
recommendations that include alternative framing and structural solutions. When testing the
retrofit this was not an option, so those suggestions for were ignored. The retrofit strategy was
based off of the CC6 guidelines, but first each strategy was tested independently alongside the
base case. E-10 generates a total energy use report which converts all energy inputs into
kBtu/ft², the results are shown in the chart below.
Strategy Tested
Base Case (kBtu/f
t²)
Base Case Specs
Retrofit (kBtu/f
t²)
Base Retrofit Specs
Energy Savings
(kBtu/ft²)Walls 43.7 Uninsulated 30.5 R-21.3 Exterior,
Polyiso Foam13.2
Windows 43.7 Aluminum/no thermal break
42.5 Vinyl, Dbl. Pane N,W,E=Low-E
1.5
Roof 43.7 R-13.3 Built Up 40.9 R-53.8, Metal roof over existing
2.8
Infiltration 43.7 0.6 ACH est. 41.0 0.3 ACH est. 2.7Thermal Mass 43.7 25% carpeted 42.0 Remove carpet 1.7HVAC 43.7 16 SEER,
unsealed ducts, stock fan
42.5 16 SEER, sealed ducts, upgraded fan
1.2
Comfort 43.7 Comfort=70°/ 40.2 Comfort=68°/78° 3.5
32
Settings 75° Setback=68°/78
°
Setback=65°/82°
Hot Water 43.7 80% eff. gas heat
40.2 Solar/gas backup 3.5
Light Bulbs 43.7 Incandescent 42.1 LED 1.6User Loads 43.7 Standard
appliances/plug loads
40.1 Energy Star appliances, smart
power strips
3.6
Figure 13. Individual Strategy Comparisons
The first strategy tested was wall insulation. To slow heat gain through the block walls, it
would be applied to the exterior of the house. Three inch polyisocyanurate panels were chosen
for their R-value (R-6 to 6.5/inch), reputation for durability, and more environmentally friendly
manufacturing process (non-ozone depleting hexane blown panels vs. hydrocarbon blown
panels). This tested as the single largest energy saver in the E-10 modeling by far, representing
a 30% energy savings over the base case. There was no option in ResCheck or E-10 for taping
the seams of the panels for an airtight envelope, but it was included in the price that was
quoted. A smooth sand stucco finish would be applied over the new insulation and a light shade
of low-VOC paint sprayed over it.
Glazing was the next variable to be analyzed. Manipulating the window values in
ResCheck demonstrated good savings, however E-10 demonstrated an energy savings of only
3.4%. The fact that the house has relatively few windows and only two of them receive direct
sunlight contributed to the low savings. The glazing and window frame construction contribute
to overall efficiency, but often older windows are warped or have shifted in the opening due to
temperature extremes or the house settling, and replacing them provides the opportunity to
improve envelope performance by eliminating air gaps as well as upgrade their performance.
For this reason, despite the low performance gains, replacing the windows is still
recommended. Top-of-the-line windows can be very expensive, however the performance
increase is not often worth the cost. Usually the added cost is for premium materials and
custom colors, or options such as triple-paned glazing whose higher insulation values make
more sense in cold climates than in the desert. For this house mid-grade, double-paned, vinyl
windows were chosen. The east, west, and north windows received low-e glass, as suggested by
33
the Design Guidelines report, and the south side double-paned, regular glazed units. The vinyl
was UV resistant to increase the longevity of the window, and the frames were designed with a
number of insulating chambers that closely matched the designs of higher end systems.
Instead of removing a fairly new roof and sending it to the dump the decision was made
to build a new roof over the existing. Due to the intensive maintenance required for the existing
roof, as well as the electrical conduit running across its surface the decision was made to install
a vented and insulated metal roof system. This turned out to be the most expensive upgrade of
the entire retrofit, and there were several options that were cheaper, however the metal roof
would not require the regular maintenance other roof types require, and if installed properly
would more than likely last for the owner’s lifetime. In addition to the maintenance cost savings
and its longevity, the new roof combined with the existing would have an insulation value
exceeding R-50. The roof would also be designed with a gutter system designed to direct water
towards landscaping features and fill rainwater collection barrels. The old, uninsulated, cracked
plastic and metal skylights would also be removed and replaced with slightly larger (1’x3’ vs.
1’x1’) operable, thermally broken aluminum framed units with double-paned low-e glass. The
operability would allow hot air to be exhausted and fresh air to enter.
34
Figure 14. Base Case Retrofit Floorplans
The mechanical systems had been upgraded prior to the current homeowners
purchasing the home. A three-year-old 16-SEER Trane split system handled the heating and
cooling and would continue to do so. A tankless gas hot water system was considered, but
higher upfront costs, required annual maintenance, and a payback period that can be longer
than the life of the unit meant that the existing 80% efficient GE hot water heater would stay
(Reports, 2008). A solar hot water system would fill the existing unit, only requiring gas heating
a small fraction of the year. All of the upgrades in aggregate produced a much higher ResCheck
score:
Figure 15. Retrofit ResCheck Compliance Graphic
In addition to the energy focused upgrades, water savings was also a priority. The
homeowners had already purchased new Energy Star appliances, and their clothes washer and
35
dishwasher were both rated to be more water efficient as well. All of the plumbing fixtures
would be replaced with low-flow WaterSense labeled products, and the toilet and sink would
be outfitted with a Sloan AQUS graywater system that stores water from the bathroom sink to
refill the toilet tank. Plumbing the shower for graywater collection proved to be labor intensive
and cost prohibitive at the time. It is a possibility if the homeowners decide to do a major
bathroom remodel in the future.
The Retrofit+AdditionA home has to meet many criteria before it can be truly sustainable, but it also has to be
lived in before any of its performance can be put to use. Since the average new home size in
the U.S. has risen to well over 2,000 square feet a 1,344 ft² home might have limited appeal for
many buyers. The base case home was already occupied, but in the interest of developing a
retrofit that would appeal to a larger percentage of home buyers as well as compare more
directly with green housing currently available on the market, a model that increased the
square footage of the base case was desirable. As it turned out the homeowners of the base
case house were new parents and beginning to feel the storage limitations, by today’s
standards, of a 1950s designed home. The lack of a second bathroom was also becoming an
issue since relatives were in town more often to see the baby.
Figure 16. Rendering of the Retrofit+Addition
36
The new additions were constructed to the same specs as the base retrofit: new exterior
insulation and stucco, new metal roof, upgraded windows, and patio cover are all incorporated.
The bedroom was designed to maximize daylighting and views of the Catalina Mountains, and
improve ventilation through operable clerestory windows. An issue with routing the HVAC
ductwork into the new addition meant extending the bedroom back farther than was initially
planned. The extra square footage was absorbed into a massive walk-in closet that should
alleviate some of the homeowner’s lack-of-storage issues. The bathroom was situated to
minimize new plumbing by locating it near the existing bathroom and was designed with water
saving fixtures, sink-to-toilet graywater recycling, and a graywater line from the shower would
irrigate landscaping in the front yard. The existing HVAC system was found to be oversized for
the square footage of the home, so new ducting was all that was required to supply
conditioned air to the additions. An optional single car garage adds a little security and value to
the home, and gutters, rainwater collection, and graywater plumbing from the new bath will
supply the water needs of a redesigned and xeriscaped front yard that homeowners plan to do
themselves.
The existing floorplan needed to be modified to allow access to the new master
bedroom, so the third bedroom of the base case was opened up. The tiny existing bathroom
was extended to the west by two and a half feet, adding a linen closet and a little more space.
The door to the bathroom was moved from the south wall to the west wall, opening into the
former bedroom. This allowed room for a new laundry closet and a slightly larger hot water
heater closet. The furnace closet was also demoed and relocated into the former bedroom
closet. This along with the new, slightly raised soffit would make the hallway feel a little more
spacious and provide a larger entry into the new open office. Since the new bathroom would
be blocking the window on the north wall a 2’x4’ operable skylight would be installed to bring
in natural light and fresh ventilation.
37
Figure 17. The Retrofit+Addition Floor Plans
The floor plans in Figure 16 indicates the addition and the interior design to the base
case changes in red. The patio extension added in the base retrofit is also included, as well as a
patio covering off of the new master bedroom, but is not indicated on the plans. Both were
modeled and tested to provide maximum shading in the summer while allowing for solar gain
during the winter time. Despite the square footage increase and extra energy loads for heating,
cooling, and electrical, the ResCheck compliance report indicated better code performance than
the Retrofit case.
Figure 18. Retrofit+Addition ResCheck Compliance Graphic
CostThe floor plans and material specifications for the base case, the Base Retrofit, and the
Retrofit+Addition were given to Jed Heuberger of Lloyd Construction to review and estimate
38
the costs of both upgrade cases. Mr. Heuberger has eighteen years of experience in the
construction industry, and has spent the last thirteen years as a project manager and estimator.
The numbers he calculated include materials and labor. Independent estimates were also
received for HVAC, roofing, and mechanical systems work. The table below breaks out the
costs and gives the final total.
Scope of Work Base Retrofit Retrofit+AdditionDemolition — $500Rough Carpentry $3,045 $6,030Metal Roof $24,155* $31,063*Insulation $2,538 $3,780Stucco $5,937 $7,340Paint $2,711 $3,530Electrical $3,000 $6,565Windows $5,500* $15,000*Plumbing — $2,500Mechanical $2,600 $4,000Grading/Earthwork
— $1,200
Concrete — $2,525Masonry — $8,410Millwork — $5,740*Doors — $2,650Drywall — $873Flooring — $1,298Tile (Bath) — $1,000Garage Addition — $36,812*Total $49,486 $140,816
Figure 19. Construction Costs
Items marked with asterisks are upgrades that could potentially cost less if alternative
materials and methods were used. For example, the quote for the roof was for the top of the
line, highest R-value available, heaviest gauge metal roof, while other options could reduce the
cost by several thousand dollars without reducing the performance significantly. In this instance
the homeowner preferred the metal roof so it was left in the case study.
Results
39
While the ResCheck compliance reports confirmed that the Retrofit and
Retrofit+Addition cases performed better than both the base case and the minimum code
requirements by a substantial margin, they do not indicate actual energy use. Energy-10 was
used to create detailed simulations for each case and examine energy, cost, and emissions
savings. To insure the accuracy of Energy-10’s results the actual utility bill energy totals for gas
and electric were compared to the E-10’s base case computed annual energy consumption
total. There was less than an 8% difference between the two sets of data so the data output
was deemed reliable. (Appendix, Table 4.)
The Base Case vs. the Base Retrofit:
Figure 20. Base Case vs. Retrofit Annual Energy Use
The annual energy consumption for the Base Retrofit was a surprising 69.8% less than
the base case, dropping from 43.7 kBtu/ft² to 13.2 kBtu/ft² (see Figure 19). Even
acknowledging that 16% of the savings is attributed to hypothetical changes in user behavior, it
still represents a decrease of more than 50%. Heating and cooling loads were reduced by 75%,
40
greatly contributing to the overall energy savings.
Figure 21. Base Case vs. Retrofit Annual Electricity Use
The graph above shows the electricity savings from switching to LED lighting, reducing
plug loads, and installing a higher efficiency fan. The combination of insulation, upgraded
windows, and raising the thermostat from 75°F to 78°F saw a drastic drop in the cooling energy
requirements of the home. Combined, these strategies lowered the estimated annual electricity
usage from 9,903 kWh to 2,990.71 kWh. To reach net zero energy consumption a roughly
2.75kW PV solar system would be needed (Solar-Estimate, 2015). There are a few ways to go
about obtaining solar power to make up the difference. Tucson Electric Power has a program
that adds $3 per month to for each block of solar power purchased, and each block covers 300
kWh each month. For the Base Retrofit two blocks would be necessary, one to cover electric
usage and the other to offset natural gas consumption (see Appendix 5). This would add $6
dollars to a bill that will average around $33 per month. For an annual total of $468 dollars the
Base Retrofit can attain net zero energy consumption using this method. The benefits of going
directly through the power company are that they own and operate the solar generating
capabilities and they are offsite, so no installation is required. The drawback is that the actual
power the home is using may or may not actually be solar, since in reality is what you are
41
paying for is an allotment of their entire electricity generation, and the portion you receive is in
theory produced by solar.
Another option is buying or financing an adequately sized PV array for the home. Solar-
Estimate.org is a website developed with support from the Department of Energy that has a
very easy to use calculator. It asks for location, the local electric company, and your monthly
electricity consumption and tells you what sized system you need, how much power it will
generate, initial cost, and any tax credits available (Solar-Estimate, 2015). The AZ Personal Tax
Credit it listed is no longer available, so it is unclear how often the site is updated. The
calculator also estimates how long it will take before the system pays for itself, in the Base
Retrofit’s case just over 13 years.
Figure 22. Solar-Estimator Graphic
By comparison, a PV system sized to offset the total energy consumption (gas and
electric) of the base case would be sized around 8.2kW and cost more than double what is
required for the Base Retrofit. Going the utility provider route would result in a $24 monthly
solar premium on top of an average bill of around $109. Even without pursuing any of the
various solar options the homeowners will see a noticeable decrease in their annual energy bill.
Figure 22 compares the reduction in energy use and cost between the base case and the Base
Retrofit (See Appendix, Table 4 for the formulas and values used to create Figure 22). Electric
bills will average $76 per month less than what the owners were previously used to, amounting
42
to an annual savings of more than $900. Natural gas bills that average $33.30 will drop by
nearly two-thirds.
Case Study
Electricity Usage (kWh)
Electricity Cost
Natural Gas Usage (therms | kWh)
Natural Gas Cost
Decrease from Base Case
Total Utility Costs
Base Case 9,903.00 $1,307.20 207 | 6,065.22 $471.55 - $1,778.75Base
Retrofit 2,990.71 $394.77 62.51 | 1,831.58 $142.40 69.80% $537.17Figure 23. Base Case vs. Retrofit Utilities Use & Cost Comparison
The environmental benefits of the Base Retrofit are also impressive. Energy-10
estimated a substantial 65% reduction in CO2 emissions over the Base Case (Figure 23),
essentially mirroring the savings seen in annual energy consumption. By weight, carbon
emissions are reduced by 4.8 tons annually through energy efficiency strategies alone. There
are also the resource and carbon emissions savings of retrofitting compared to building new
that were discussed earlier. Using the 7 gallons per kWh figure (P. Torcellini, 2003) the Base
Retrofit is capable of saving nearly 50,000 gallons of water each year just through its energy
cuts. Additional savings from the installation of WaterSense labeled fixtures is estimated to
save another 30% off of the homeowner’s water bill, reducing consumption by just under
10,000 gallons each year. The owners of the base case are extremely frugal with water and
have minimal irrigation requirements for their landscaping resulting in an annual bill that is
almost 60% less than average of 82,000 gallons per year in Tucson (see Appendix 4). An
average home in this area could expect to savings of nearly 25,000 gallons per year. In terms of
cost savings the Base Retrofit case could expect to save around $200 per year, while a home
consuming the Tucson average could see savings approaching $550 annually.
43
Figure 24. Base Case vs. Retrofit Annual Emissions Results
Retrofit+Addition:The Base Retrofit is the core of the Retrofit+Addition, so their energy performance was
expected to be relatively close, but a -0.75% performance drop was excellent considering the
additions added 531 ft² of space requiring lighting, air conditioning, and heating. Since the
Base Retrofit has been discussed in detail, this section will focus on the additions and the
differences between the Retrofit+Addition, the base case, and the Base Retrofit.
Figure 25. Retrofit+Addition Annual Energy Use
44
Energy-10 always runs its own concurrent Low-Energy Case unless the user inputs a
second building. Because of the design changes it was impossible to compare the base case and
the Retrofit+Addition side-by-side in E-10. For this section ignore the values for the Low-Energy
Case as they are not relevant for comparison except to show that the Retrofit+Addition
significantly outperforms even the E-10 upgraded case. As Figure 25 shows, the total annual
energy use was one tenth of a kBtu higher than the Base Retrofit.
The bedroom and bathroom additions were designed with the same envelope as the
Base Retrofit, which tested as the highest energy saver of all the strategies implemented. All
new glazing was primarily north facing to take advantage of daylighting without any direct solar
gain, except for a French door in the south wall of the bedroom. The patio cover was sized to
block summer sun, but during the winter time the sun will drop low enough to cast light twelve
feet deep into the room, warming the concrete floors. The heating and cooling loads on the
Retrofit+Addition are actually lower than the Base Retrofit. The best explanations for this are
that A) the bedroom addition and the garage provide some shading that didn’t exist before, and
B) the existing HVAC system was oversized by more than a 25% according to the HVAC
technician that did the estimating. Oversized systems are as inefficient as undersized, so the
extra square footage actually ended up sizing the house properly for the HVAC. Not generally
the approach to take, but in this case it worked out well. New lighting was sized for the space
and provided by LED fixtures and bulbs, however the interior remodel along with the addition
added five more fixtures which was about a third more than the Base Retrofit included, and is
reflected in the increased lighting load. The “other” category also had a noticeable increase due
to bedroom and bathroom plug loads, and a new bedroom ceiling fan and bathroom exhaust
fans (one was added to the existing bathroom). Water consumption was estimated to be
around the same as the Base Retrofit. The energy consumption and utility costs differences
between the base Retrofit and the Retrofit+Addition are negligible (see Figure 25), and both
versions put the base case to shame, but there was one area that there was a noticeable
difference.
45
Figure 26. Side-by-Side Utilities & Cost Comparison - All Three Case Studies
Emissions were the only area where the Base Retrofit significantly outperformed the
Retrofit+Addition, which produced nearly 2.5 tons more C02 per year (Figure 25). Still, the
Retrofit+Addition saw 2.3 tons annual savings over the base case. On a square footage basis the
Base Retrofit was first at 3.82 lbs/ft², the Retrofit+Addition was second with 5.39 lbs/ft², and
the 10.98 lbs/ ft² of CO2 producing base case was last. Despite the efficiency increases in
heating and cooling, the extra space still requires additional conditioning and lighting that, using
the prevalent sources of energy, increases the overall carbon footprint of the Retrofit+Addition.
Figure 27. Retrofit+Addition Emissions Results
Case Study
Electricity Use (kWh)
Electricity Cost
Natural Gas Use (therms | kWh)
Natural Gas Cost
Decrease from Base Case
Total Utility Costs
Base Case 9,903.00 $1,307.20 207 | 6,065.22 $471.55 - $1,778.75Base
Retrofit 2,990.71 $394.7762.51 |
1,831.58 $142.40 69.80% $537.17Retrofit+Addition 3,010.51 $397.39 62.93 | 1843.89 $143.35 69.60% $540.74
46
Figure 28. Retrofit+Addition Rendering
The Retrofit+Addition end result is a 1,875 square foot aesthetically and functionally
modern home built around the bones of a 61 year old house. It is more livable, and adds more
storage and convenience while outperforming the base case in every metric. The Base Retrofit
offers the best combination of resource, emissions, and cost savings but may have limited
appeal due to its size. The table below gives the summary for all three case studies.
Monthly Monthly AnnualCase Study Electricity (kWh) Gas (therms) Water (cu.ft.) Utility Cost Utility CostBase Case 9,903 207 4,400 $207.95 $2,495.37
Base Retrofit 2990.71 62.51 3,080 $86.61 $1,039.21Retrofit+Addition 3010.51 62.93 3,100 $90.07 $1,080.84
Figure 29. Summary of Results
Conclusions The need for sustainable solutions has been and continues to be well established, yet
the United States lags far behind several other developed nations when it comes to
implementing them. We are by every metric living unsustainably. The built environment, due to
its thirst for energy and resources, is one area where changes can make major and immediate
47
positive impacts in every sphere of sustainability. Commercial construction has been an early
adopter of sustainable building practices in the U.S., but the residential sector has lagged
behind. Perceptions of higher costs and lower returns are not always inaccurate, but they don’t
have to be a universal truth. While some builders will charge $500,000 or more for a “green”
home, that kind of investment is not necessary to sustainably retrofit a home. It could be
argued if sustainability is unaffordable then it’s not really sustainable at all, yet the trend seems
to be green living can only be had at a premium price. The graph below illustrates the
differences between market prices and the construction costs determined in this study. Even
tacking on an additional 10% for profit over what was already built in, the case studies still
provide more value at affordable or close to affordable (on a median income) price tags.
$- $100,000.00 $200,000.00 $300,000.00 $400,000.00
Green Housing Affordability in Southern Arizona
Low Range High Range
Figure 30. Green Housing Affordability in Southern Arizona
It is very possible to retrofit a moderately sized existing home to reduce its energy
consumption by fifty percent or more, substantially lower its water consumption, and do it all
well within the price range of a median income earner. Additionally, with the simple layout and
structural design of the older homes in southern Arizona, more square footage can easily be
incorporated and still maintain close to the same energy and water efficiency performance as a
48
basic retrofit while still costing significantly less than what is currently being offered on the
market, in some cases hundreds of thousands of dollars less. Figure 29 reiterates the energy
and environmental savings that this study found possible.
Total Energy (kBtu/ft²) Electricity (kWh/ft²) CO2 Emissions (tons x 1000)0
5
10
15
20
25
30
35
40
45
50
Energy & Emissions: Comparisons of 3 Case Studies
Base Case Base Retrofit Retrofit+Addition
Figure 31. Energy & Emissions: 3 Case Studies
Economically it may make more sense for some homeowners to spend a few thousand
dollars upgrading insulation, replacing some windows, and sealing the building envelope and
figuring out their electricity usage from there. Then going through a utility or purchasing or
renting a PV system may be the more cost effective route rather than an intensive energy
retrofit. On the other hand, developers may find that investing $50,000 to $150,000 into
retrofitting the right properties may actually be more profitable than building new if they can
keep the final cost closer to the median income affordability. The profitability would come from
two factors, the first being that a more affordable price point would mean more potential
buyers, and the second is the home’s green selling points, especially the ones that lower a
49
prospective homeowner’s monthly bills. This is where more local, state, and federal tax breaks
and incentives would go a long way.
The lack of Federal and State incentives is a travesty. The environmental, social, and
economic benefits of building and living greener are countless, yet fossil fuel companies are
receiving 78% more in government subsidies than sustainable initiatives (Initiative, 2015). With
homeowners saving more than $100 per month on utilities to be spent elsewhere, reducing
annual water use by between 60-75 thousand gallons per household, and reducing energy
consumption and the related emissions by two-thirds, it seems like a no brainer. If just ten
percent of the homes nearly 84,000 homes built before 1970 in Tucson were to receive deep
energy and water retrofits, regionally it would mean 630 million gallons of water saved per
year, a 40,320 ton annual reduction in carbon emissions, and more than $12 million dollars a
year savings for consumers.
Sustainable retrofits will not be able to provide all of the housing needs for the growing
population, but the environmental, economic, and social benefits that they have the potential
to provide should make them serious consideration for homeowners, homebuyers, and
policymakers. Southern Arizona is especially well situated to take advantage of abundant
sunshine to reduce their reliance on water intensive thermoelectric power production, and to
become a national leader in renewable energy use and raising home efficiency standards, but it
has to start with affordability. The climate change and resource challenges the world faces
require sustainable solutions, but if only a small fraction of the population have the solutions
available to them then only a small fraction of the problem is going to be addressed.
Sustainable retrofitting is one piece of the puzzle, and one that can be available to a greater
percentage of the population.
Limitations This is one home out of thousands of potential candidates for a sustainable retrofit, and
each home is unique. The square footage, solar orientation, and existing upgrades will vary
from house to house. Some older properties will need major plumbing and electrical
50
renovations for any upgrades to be effective, others may require structural repairs or
improvements before roofing, solar, or insulation can be considered.
Any comparison of real estate has to factor in location. Some of the green home listings
were in prime downtown or foothills locations and as such command a premium price. Still,
some of the price tags far exceeded the value added by location.
An energy audit was considered for the base case, but due to the fact that none of the
suggested strategies could actually be implemented in time to be retested it was decided that
time and effort would be better spent into designing and testing the retrofit strategies using 3D
and energy modeling software.
Energy-10 is a very powerful tool, and provided at a basic level everything this capstone
required of it, however it is no longer supported by the Department of Energy and several
features that would have generated deeper levels of information, produced helpful graphs, or
saved hours of time manually calculating data either didn’t work at all or had glitches at various
inopportune times.
Energy-10 has a limited materials list. Every effort was made to create accurate inputs
when there were no existing E-10 material profiles, but performance variables can vary widely
between manufacturers. In those instances a median value was selected.
Cost is still a limitation, despite the evidence showing that a basic sustainable retrofit
can generally be accomplished within the budget of a median wage earner. The financial
assumptions made to establish affordability for median wage earners were generous, possibly
too much so. Hard numbers for median and average debt to income ratios were unavailable.
Even with the best case median income financial scenario, sustainable techniques and
strategies such as whole house energy monitoring and remote water tracking, graywater
retrofits, and structural design changes to improve air flow and natural lighting will more than
likely have to be left on the table. It may not be feasible in some cases to replace every fixture
in the house with WaterSense labeled products, nor will every project have the budget to
replace entire mechanical systems or appliance packages with Energy Star rated units.
51
Another major assumption, and one of the largest variables found during Energy-10
testing, was user loads, in particular thermal comfort. The willingness of homeowners to adapt
to a wider range of thermal comfort and reduce the use of heating and cooling, as well as
appliance use and other user controlled variables, have a major effect on overall energy use.
Behavioral modifications were assumed in this study, but were not weighted too heavily and
the effects they had on the outcomes were indicated.
Recommendations Further study into the water-energy nexus focusing on quantifying the reciprocal effects
saving energy has on water supplies and vice versa would be a powerful tool in
considering the greater impact sustainable retrofits can have at local and regional levels;
A study of residential vs. commercial retrofits from a business model perspective might
shed some light on why the commercial sector has seen far greater growth in green
retrofits, and what lessons could be applied to residential;
Investigate incorporating city planning with large scale neighborhood retrofit projects;
Investigate more detailed life cycle analyses of retrofits vs. new construction;
A social comparison of developed nations with differing degrees of investment into
sustainable infrastructure, taking a look at health, happiness, education, wealth, crime,
and other statistics to determine if and to what degree a society experiences an
improved quality of life with a higher level of commitment to sustainability;
Incorporating interviews with homeowners, prospective homebuyers, and construction companies into a study of sustainable retrofitting would be useful.
i
Appendix
Table 1. American Housing Survey: Tucson
ii
Table 2. Green Listings in Southern Arizona
iii
Table 2. Green Listings in Southern Arizona (continued)
iv
Table 3. Base Case Actual Electric and Gas Consumption vs. Energy-10 Outputs
1 kWh = 3412.142 Btu 1 therm = 99976.1 Btu Energy-10 Base Case Annual Energy Consumption = 43.7 kBtu/ft² Base Case square footage = 1,344 Energy-10 Base Case Total Btu = 43.7 kBtu/ft²x 1,000 x 1,344 ft² = 58,732,800 Btu Actual Base Case = 9,903 kWh + 207 therms
= (9,903 kWh x 3412.142 Btu/kWh) + (207 therms x 99,976.1 therms/Btu)
= 33,790,442.23 Btu + 20,695,052.70 Btu
= 54,485,494.93 Btu
Actual Base Case kBtu/ ft²= 54,485,494.93 Btu/1,344 ft²/ 1000 = 40.5 kBtu/ ft² Actual vs. Energy-10 = 40.5 kBtu/ ft² / 43.7 kBtu/ ft² = 92.7% accurate
Table 4. Utility Costs
Month Electric (kWh) Gas (therms)Jan 553 63 Feb 470 36 Mar 466 21 Apr 515 10 May 669 8 Jun 1,242 7 Jul 1,457 6
Aug 1,350 8 Sep 1,122 6 Oct 891 7 Nov 573 10 Dec 595 25
Annual Total 9,903 207 Monthly Total 825.25 17.25
Annual Btu's 33,790,442.226 20,695,052.70
Annual Electric + Gas Btu's 54,485,494.93
v
Base Case
TEP Average Monthly Rate (including taxes and service charges): $0.132/kWh Southwest Gas Average Monthly Rate (including taxes and service charges): $2.278/therm
Electricity
Usage (kWh)
Gas Usage (therms)
Month Monthly Bill Monthly BillWater
Usage (ft²) Monthly BillJan 553 $73.00 63 $143.51 200 $52.98Feb 470 $62.04 36 $82.01 300 $58.67Mar 466 $61.51 21 $47.84 400 $60.84Apr 515 $67.98 10 $22.78 300 $58.67May 669 $88.31 8 $18.22 400 $60.84Jun 1,242 $163.94 7 $15.95 600 $65.19Jul 1,457 $192.32 6 $13.67 500 $61.81
Aug 1,350 $178.20 8 $18.22 500 $62.94Sep 1,122 $148.10 6 $13.67 300 $58.67Oct 891 $117.61 7 $15.95 300 $58.67Nov 573 $75.64 10 $22.78 300 $58.67Dec 595 $78.54 25 $56.95 300 $58.67
Annual Usage 9,903 $1,307.20 207 $471.55 4,400 $716.62Monthly Average 825.25 $108.93 17.25 $39.30 366.67 $59.72
Base Case Energy Cost/ ft² = ($1,307.20 + $471.55)/1,344 ft² = $1.323/ ft²
Water Conversion: Cubic feet to gallons:1 cubic foot = 7.48052 gallons, Base Case = 32,914 gallons/year
Tucson Average Water Consumption: 10,970 cubic feet x 7.48052 gallons = 82,016 gallons/year
Retrofit Case
Base Case Annual Energy Use (E-10 results)= 43.7 kBtu/ft² Base Retrofit Annual Energy Use (E-10 results) = 13.2 kBtu/ft² Percent Decrease in Energy Use = 1 - Base Case Annual Energy Use/Retrofit Annual Energy Use = 1 –
(13.2 kBtu/ft² / 43.7 kBtu/ft²)
= 69.8%
Base Retrofit Electricity Costs = ((1 - 0.698) x 9,903 kWh)($0.132/kWh)
= (2990.71 kWh)($0.132/kWh)
= $394.77
vi
Table 4. Utility Costs (continued)
Base Retrofit Natural Gas Costs = ((1- 0.698) x 207 therms)($2.278/therm)
= (62.51 therms)($2.278/therm)
= $142.40
Base Retrofit Water Costs = (base case –( base case x 30% est. savings))($0.163/cubic foot) = (4,400 cu.ft. – (4,400 cu.ft. x 0.30)($0.163/cu.ft.) = (3,080 cu.ft. x $0.163)
Cost = $502.04
Total Gallons = 23,040/year
Base Retrofit Total Utility Costs = $394.77 + $142.40 + $502.04
= $1,039.21
Retrofit+Addition Case
Base Case Annual Energy Use (E-10 results)= 43.7 kBtu/ft² Retrofit+Addition Annual Energy Use (E-10 results) = 13.3 kBtu/ft² Percent Decrease in Energy Use = 1 - Base Case Annual Energy Use/Retrofit+Addition AEU
= 1 – (13.3 kBtu/ft² / 43.7 kBtu/ft²)
= 69.6%
Retrofit Electricity Costs = (1 - 0.696 x 9,903 kWh)($0.132/kWh)
= (3010.51 kWh)($0.132/kWh)
= $397.39
Retrofit+Addition Natural Gas Costs = ((1- 0.696) x 207 therms)($2.278/therm)
= (62.93 therms)($2.278/therm)
= $143.35
Retrofit+Addition Water Costs = (base case –( base case x 30% est. savings))($0.163/cubic foot) = (4,400 cu.ft. – (4,400 cu.ft. x 0.30)($0.163/cu.ft.) = (3,080 cu.ft. x $0.163)
vii
= $502.04
Total Gallons = 23,040/gallons per year
Retrofit+Addition Total Utility Costs = $397.39 + $143.35
= $1,042.78
Table 5. Converting Therms to kWh for Solar Sizing
viii
1 kWh = 3412.142 Btu 1 therm = 99976.100 Btu 1 kWh/1 therm = (3412.142 Btu/1 kWh)/(99976.1 Btu/1 therm) = 0.034129 kWh/therm
Base Case
207 therms / 0.034129 kWh/therm = 6,065.22 kWh
Base Retrofit
62.51 therms / 0.034129 kWh/therm = 1,831.58 kWh
Retrofit+Addition
62.93 therms / 0.034129 kWh/therm = 1843.89 kWh
ix
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