city of denver green roof review task force meeting 2...roof replacement rate 4% per year 0 0.5 1...
TRANSCRIPT
City of Denver
Green Roof
Review Task Force
Meeting 2
Denver Buildings Covered by the Green Roofs Ordinance. 1.5% annual growth assumed
Commercial, Office, School, Govt, Church, Hotel, etc
Gross Sqft CategoryCount of Buildings
in this category 2014
Sum of Building
Gross sqft 2014
Sum of roof sqft
2014
Sum of Building
Gross sqft 2050
Sum of roof sqft
2050
Size of green
roof required
25,000-49,999 sqft 624 22,238,736 10,093,708 38,009,103 17,251,555 20%
50,000-99,999 sqft 448 31,506,676 11,398,145 53,849,306 19,481,020 30%
100,000-149,999 sqft 200 24,253,442 7,090,332 41,452,517 12,118,367 40%
150,000-199,999 sqft 101 17,612,433 4,544,787 30,102,106 7,767,675 50%
200,000 sqft or greater 271 153,477,564 22,289,298 262,314,573 38,095,520 60%
Residential (does not apply to residential building with "a height less than or equal to the greater of four stories or 50 feet.")
Gross Sqft CategoryCount of Buildings
in this category 2014
Sum of Building
Gross sqft 2014
Sum of roof sqft
2014
Sum of Building
Gross sqft 2050
Sum of roof sqft
2050
Size of green
roof required
25,000-49,999 sqft 77 2,875,797 532,014 4,915,138 909,286 20%
50,000-99,999 sqft 136 9,831,811 1,604,404 16,803,937 2,742,150 30%
100,000-149,999 sqft 49 6,091,488 808,066 10,411,203 1,381,098 40%
150,000-199,999 sqft 25 4,319,764 499,047 7,383,079 852,941 50%
200,000 sqft or greater 41 17,705,586 1,870,327 30,261,317 3,196,650 60%
Industrial
Gross Sqft CategoryCount of Buildings
in this category 2014
Sum of Building
Gross sqft 2014
Sum of roof sqft
2014
Sum of Building
Gross sqft 2050
Sum of roof sqft
2050
Size of green
roof required
25,000-249,999 sqft 869 70,575,009 33,968,542 120,622,538 58,056,978 10%
greater than 250,000 sqft 165 90,114,205 31,222,077 154,017,751 53,362,886 capped at 25,000
Climate Change
Green Roof and Photovoltaic Panels Intro
Denver’s Core: GHG Emissions SourcesGreen Roof &
PV Intro
“In 2013, Denver’s GHG emissions were below those of 2005, declining from
13.20 million mt-CO2e in 2005 to 12.985 million mt-CO2e in 2013.”
The goal is 80% below 13.20 million mt-CO2e by 2050.
Green Roof Impact on GHG Emissions
How do green roofs potentially impact
GHG emissions?
Energy use of the building
• Heating Energy Use
• Cooling Energy Use
Conversion of CO2 to O2 during nighttime
Green Roof &
PV Intro
Conversion CO2 to O2
• Green roofs are expected to absorb and store carbon in
plants and soils and thereby reduce the high CO2
concentration levels in big cities.
• Study showed Sedum plants have high rates of CO2
emission at daytime, when CO2 concentration in the city
is the highest.
• CO2 emissions were not fully compensated by the
nighttime uptake.
• Carbon sequestration may only be a secondary benefit of
green roofs.
• Other plant species than Sedum should also be
considered for use in green roofs, especially in
Mediterranean and other semi-arid climates.
Green Roof &
PV Intro
Source: Whittinghill, Leigh et al. 2014. "Quantifying carbon sequestration of various green roof and ornamental landscape
systems." Landscape and Urban Planning. Vol. 123.
Heating Energy Savings
• Depending on what the green roof is
like, there may or may not be a heating
energy benefit
• There could even be a penalty for some
types of inverted roofs
• In any case, increasing roof insulation
will be more cost effective
• No benefit from partial green roofs
Green Roof &
PV Intro
Cooling Energy UseGreen Roof &
PV Intro
Image Source: Heidarinejad, Ghassem, and Arash Esmaili. 2016. "Assessment of green roof energy savings compared to
conventional roof." eSim.
Roof Temperatures in SummerGreen Roof &
PV Intro
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Ro
of Te
mp
era
ture
( F
)
Time of Day
Conventional Roof Green Roof
Cooling Energy Savings
Cooling energy savings results from:
• Lower roof temperatures during the summer months
• Less heat transferred to space below
• Less heat needing to be removed from space below.
Green Roof &
PV Intro
Water Pumping Energy
Water pumping energy includes:
• Energy to deliver potable water to site
• Energy to pump water to the roof
750 kWh per million gallons of potable water is
required to deliver water to site*
Green Roof &
PV Intro
*Source:
https://coloradowater.charityfinders.com/documents/Annual%20Conference/2011%20Conference%20Presentation
s/2011%20Conference%20Presentations%20Wednesday/CO_WatershedOct2011_EnergyMgmt_BP.pdf
Green Roof Only: GHG Emissions
Reduction Green Roof &
PV Intro
Parameter Assumption
2005 GHG Emission Value 13.2 million mt-eCO2
New Construction Growth Rate 1.5% per year
Roof Replacement Rate 4% per year
0
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0.015
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0.035
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Cu
mu
lati
ve
GH
G R
ed
uc
tio
n fro
m 2
00
5
Em
iss
ion
Va
lue
(%
)
Year
Cooling Savings
Loss for Water Pumping
Savings for CO2->O2
Heating Savings
Total Savings
PV & Green Roof: GHG Emissions
Reduction Green Roof &
PV Intro
Parameter Assumption
Max PV Area 70% of green roof space
2005 GHG Emission Value 13.2 million mt-eCO2
New Construction Growth Rate 1.5% per year
Roof Replacement Rate 4% per year
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lati
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uc
tio
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iss
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lue
(%
)
Year
PV Savings
Cooling Savings
Loss for Water Pumping
Savings for CO2->O2
Heating Savings
Total Savings
GHG Reduction Comparison at Year
2050Green Roof &
PV Intro
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Green Roof Only PV + Green Roof
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ar
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)PV Savings
Cooling Savings
Savings for CO2->O2
Heating Savings
Heat Island Effect
City of DenverHeat Island
Effect
Image Source: Google Map
City of Denver - DowntownHeat Island
Effect
Image Source: Google Map
City of Denver - ResidentialHeat Island
Effect
Image Source: Google Map
Urban Heat IslandHeat Island
Effect
Image Source: Heidarinejad, Ghassem, and Arash Esmaili. 2016. "Assessment of green roof energy savings compared to
conventional roof." eSim.
Urban Heat IslandHeat Island
Effect
Image Source: Heidarinejad, Ghassem, and Arash Esmaili. 2016. "Assessment of green roof energy savings compared to
conventional roof." eSim.
Urban Heat IslandHeat Island
Effect
Source: Kenward, Alyson et al. 2014. “Summer in the City: Hot and Getting Hotter." Climate Central.
Urban Heat IslandHeat Island
Effect
Image Source: Kenward, Alyson et al. 2014. “Summer in the City: Hot and Getting Hotter." Climate Central.
Based on: Natural Resources Canada. 2004. “Adapted from Climate Change Impacts and Adaptation: A Canadian Perspective.” Edited by
D. S. Lemmen and F. J. Warren. Ottawa. ON: Climate Change Impacts and Adaptation Program.
Urban Heat IslandHeat Island
Effect
The top 10 cities with the most intense summer urban
heat islands (average daily urban-rural temperature
differences) over the 2004-2014 are:
• Las Vegas (7.3°F)
• Albuquerque (5.9°F)
• Denver (4.9°F)
• Portland (4.8°F)
• Louisville (4.8°F)
• Washington, D.C. (4.7°F)
• Kansas City (4.6°F)
• Columbus (4.4°F)
• Minneapolis (4.3°F)
• Seattle (4.1°F)
Source: Kenward, Alyson et al. 2014. “Summer in the City: Hot and Getting Hotter." Climate Central.
Temperature data is drawn from the Applied Climate Information Systems database (ACIS), which
itself draws on data from NOAA/NCDC’s Global Historical Climatology Network (GHCN).
Roof Temperatures in SummerHeat Island
Effect
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Ro
of Te
mp
era
ture
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)
Time of Day
Green Roof Conventional Roof
Surface Temperature: Night and DayHeat Island
Effect
Source: Mehdi Heris and Austin Troy, CU Denver Dept of Urban and Regional Planning
Nighttime August 2003 Daytime June 2012
Daytime Surface TemperatureHeat Island
Effect
Source: Mehdi Heris and Austin Troy, CU Denver Dept of Urban and Regional Planning
Color coded differently
Nighttime Surface TemperatureHeat Island
Effect
Source: Mehdi Heris and Austin Troy, CU Denver Dept of Urban and Regional Planning
Color coded differently
Typical Nighttime Heat Island ProfileHeat Island
Effect
BaltimoreDenver
Distance to CBD Distance to CBD
Source: Mehdi Heris and Austin Troy, CU Denver Dept of Urban and Regional Planning
Water Quality
GREEN ROOFSBenefits and Impacts
Water Quantity and Quality
Perviousness/Imperviousness
• Pervious surfaces allow water soak into the ground, impervious surfaces do not, instead creating runoff.
Pervious Surfaces Impervious Surfaces
Grass Roads and Sidewalks
Dirt, Sand, or Gravel Roofs
Parking Lots and Driveways
Runoff Reduction
• Reduces Peak Flows by Delaying Runoff
• Decreases Amount of Runoff
Impact varies depending on how recently the previous storm occurred.
USGS, 2010
Existing
Basin Area 626 Acres
Amount of Impervious Area 502.3 Acres
Percent Imperviousness 80.2%
Number of Bldgs. >25,000 sq. ft. 67
Roof Area , Bldgs. >25,000 sq. ft. 147.7 Acres
Assumptions:All structures completely within drainage basinAll structures in basin are one story
With Green Roofs
Required Green Roof Area 62.4 Acres
Impervious Area with Green Roofs 439.9 Acres
Percent Imperviousness 70.3%
Addition of green roofs results in a 10% decrease in basin imperviousness
Reduction in Amount of Pollutants Reaching Denver’s Streams and Lakes
Green / Conventional Roof Comparison• Decreased runoff
• Some water that falls on green roofs will evaporate, not runoff
• Treatment of Water
• Runoff from green roofs contains lower levels of metals
• Solids retained more effectively by green roofs
• Green roofs may or may not have a benefit for nitrogen and phosphorus
• Nutrient levels in discharges from green roofs decrease as a function of time
Reduces Localized Flooding
• Delayed runoff may result in reductions in localized flooding• Some of Denver’s storm sewers designed to contain the 2 or 5 year storm
event• Larger storm events result in localized neighborhood flooding
• Delaying runoff it reduces volume of water to be conveyed
Summary
• Green Roofs• Decrease runoff
• 10% reduction in imperviousness in one Montbello storm drainage basin
• Impact varies depending on how recently the previous storm occurred.
• Benefits• Reduction in amount of pollutants reaching Denver’s streams and lakes
• Decreased runoff
• Provides treatment for some pollutants
• Delayed runoff may reduce localized flooding
QUESTIONS?
Jon NovickEnvironmental Administrator – Water Quality
Denver Department of Public Health and Environment200 W. 14TH Ave
Dept. 310Denver, CO 80204
Water Quantity
2017 Potable Water Supply
2/7/201840
Acr
e Fe
et
300
600
900
1200
Data and Assumptions
2/7/201841
• 2014 roof print GIS file
• Calculated Gross Floor Area (GFA)
• Green roof applied to correct roof % category based on ordinance
• All buildings have max green roof, not solar or a combination
• Assumed future buildings will fall into the same building size categories
• 1.5% growth per year
• 95% of installed green roofs will be sedum or native plant equivalent (3.12 gallons per sqft)
• 5% of installed green roofs will agricultural or turf grass equivalent (18 gallons per sqft)
Added Potable Water Demand
2/7/201842
Building sqft (existing
2014)
New Water Demand AF
Building sqft 2014-2045
Future Water
Demand AF
Est. Building sqft 2045
2045 Green Roof Water Demand AF
Commercial 23,841,794 258 13,983,842 151 37,825,635 409
Industrial 2,275,023 25 1,334,361 14 3,609,384 39
Residential 7,511,113 81 4,405,466 48 11,916,579 129
Total 33,627,930 363 19,723,669 213 53,351,599 576
• Added Demand could range from 576 Acre Feet – 1836 Acre Feet
• Most likely scenario assumes
• 95% sedums and native plants• 5% urban agriculture and water intensive
2017 Potable Water Demand
2/7/201843
Acr
e Fe
et
300
600
900
1200
Potential Risks
2/7/201844
• Added potable water demand during our peak demand – Can demand be met with
alternative water sources?
• Drought implications– Does Denver Water need to
change our operating rules to reflect best management practices?
• Water quality at the building level– Backflow preventer required for
all irrigation
• Perception that green roof are not in alignment with conservation
Potential Benefits
2/7/201845
• Water savings through reduced energy usage and cooling load reduction– Would like to see more studies
to confirm benefits
• Examples of climate appropriate landscapes
• Reduction of urban heat island could reduce cooling needs for other buildings
• Builds support for alternative water source options
Air Quality
Impact of Green Roofs on Air Quality:Compendium of pertinent studies
Gregg W Thomas – Division Director
City and County of Denver
Denver Dept of Public Health and Environment
Feb 2018
Denver’s nationally- accredited public health
department
Compendium of Studies
▪ 2017 – SoCab (L.A.) cool roofs impacts O3 and PM2.5
▪ 2016 – Montreal increased albedo AQ modeling during a heat
wave and air quality episode in 2005
▪ 2016 – Chicago green and cool roofs impacts on UHI and local
weather variables during a 3 day heatwave in 2013
▪ 2015 – Stuttgart Germany green roofs secondary effects on AQ
▪ 2014 – Urbanization impacts in 2100 for US megapolitan
areas under low and high growth scenarios (temp & precip)
▪ 2011 – US GSA report on green roofs (general not technical)
▪ 2008 – Sacramento heat island mitigation impacts on ozone
2017 South Coast Air Basin (SoCab)
▪ Small decreases in avg annual daily max T,
mixing heights, and ventilation rates
▪Due to increased UV reflectance
▪ Slight increases <0.3 micrograms/m3 for
PM2.5
▪ Both increases and decreases in ozone,
decrease in city center, increase of 0.6 ppb in
suburbs
Other Studies Findings
▪ 2016 Montreal Albedo: reduced urban heat
island (UHI); incr. and decr. in PM2.5 and
ozone
▪ 2016 Chicago Green/Cool roofs: reduced UHI,
reduced surface winds/ventilation, AQ not
modeled
▪ 2014 US Urbanization – green and cool roofs;
hybrid roofs provide greatest UHI; enough to
offset global GHG Temp increases, no AQ
▪ 2015 – Stuttgart Germany green roofs secondary effects on
AQ; urban greening and white roofs reduce average ozone;
Could increase occasional ozone peaks a few ppb locally
▪ 2011 GSA Green Roofs – general statements about reducing
all pollutants through deposition and uptake by plants
▪ 2008 Sacramento – increased urban albedo (roofs, walls,
pavement) result in decreased urban temps and 0-10%
reductions in ozone; similar to Montreal
▪ Many of these studies use historic
emissions
• Future emissions will be lower
Other Studies Findings (cont.)
Summary▪ All studies show a reduced UHI under either green or
cool roofs scenario
▪ In one study, hybrid model produce the greatest UHI
reduction
▪ Studies also show decreased wind speeds and
ventilation coefficients, result in less mixing
▪ Mixed results for air quality, both increases and
decreases, though most changes are small and would
not be expected to affect AQ attainment in Denver
Effects on Air Quality
• Lessening the urban heat island effect mid-day can lessen the
production of excess ozone generated by photochemistry, which is
highly temperature dependent.
• Increased surface friction offered by green roofs can lessen wind
speeds and ventilation coefficients, hampering the dispersion of
pollutants.
• Green roofs can remove air pollutants from the atmosphere through
direct impact (deposition) and plant respiration (uptake). Some papers
make reference to soil erosion from green roofs which contribute
particulate pollutants to the urban environment.
• Resultant effects on air quality attributed to green roofs are small and
mixed for air quality, with both increases and decreases.
• An investment in improving air quality green roofs provide little benefit
at great cost. As a solution, green roofs are aimed at emissions in a
dispersed state – in a high state of entropy. Treating air contaminants
before dispersal is more cost-efficient (e.g. electrostatic precipitators,
wet scrubbers, baghouses). Engineered solutions like more efficient
vehicle engines, cleaner fuels, and more efficient transportation modes
are also more cost-efficient.
Air Quality
Food Production
Most installations are independent
of regulations, typically mission-
driven
Represents a significant O&M
investment by owner/operator
Due to external influences, difficult
to predict uptake and growth
URBAN FOOD GARDENS
Cost Evaluation
Cost Breakdown and Net Present Value Calculation
Cost Evaluation Overview
In this section, we will:
• Show fees in lieu of compliance
• Show typical costs for adding a green roof and
PV for four representative buildings: apartment,
industrial, retail, and office.
• Compare these costs to conventional roof
replacement costs for existing buildings
• Compare these costs to total construction costs
of a new building
• Show a life cycle cost analysis of green roofs
and PV
Cost Evaluation
Representative Buildings
Apartment
55,000 square feet, 5 floors, roof is 11,000 sq ft.
Green Roof Coverage requirement: 30% or 3,300 sq ft.
Industrial or Retail
150,000 square feet, 1 floor, roof is 150,000 sq ft.
Green Roof Coverage requirement:
• 10% for Industrial or 15,000 sq ft.
• 50% for Retail or 75,000 sq ft.
Office
300,000 square feet, 15 floors, roof is 6,000 sq ft.
Green Roof Coverage requirement: 60% or 3,600 sq ft.
Cost Evaluation
$25/ft2 of green roof area
Cost Evaluation Fee in Lieu of Compliance
Building 1:
Apartment
Building 2a:
Industrial
Building 2b:
Retail
Building 3:
Office
$82,500 $375,000 $1,875,000 $90,000
Source DescriptionBuilding 1:
Apartment
Building 2a:
Industrial
Building 2b:
Retail
Building 3:
Office
Engineering
Company #1Engineering studies $5,000-$8,000 $15,000-$20,000 $15,000-$20,000 $5,000-$8,000
Engineering
Company #1
Fees are only for studies and do not
include producing construction
documents, permit sets and construction
administration.
No structural documents: fee includes
investigation of existing framing
conditions.
$1,800-$2,500 or
$3,600-$5,000
(no structural
documents)
$4,000-$6,000 or
$8,000-$12,000
(no structural
documents)
$4,000-$6,000 or
$8,000-$12,000
(no structural
documents)
$4,000-$5,000 or
$8,000-$10,000
(no structural
documents)
Roof Consultant
#1
Structural engineering cost to prove the
building will not support a green roof.$15,000-$40,000 $15,000-$40,000 $15,000-$40,000 $15,000-$40,000
Engineering
Company #3
Potential structural engineering costs of
evaluating existing buildings for the
incorporation of green roofs and/or solar
systems.
$20,000 $25,000 $40,000 $20,000
Cost Range ($) $1,800-$40,000 $4,000-$6,000 $4,000-$40,000 $4,000-$40,000
Cost Evaluation Structural Assessment Costs
Green Roof and PV Scenarios
Baseline: Conventional Roof
Scenario 1: Green Roof Only
• Green roof is 100% of required green roof space
Scenario 2: PV & Green Roof
• PV is covering 70% of required green roof space
• Green roof is covering 30% of required green roof space
Cost Evaluation
Cost Evaluation Existing Buildings
DescriptionBuilding 1:
Apartment
Building 2a:
Industrial
Building 2b:
RetailBuilding 3: Office
Conventional Roof Replacement Cost ($) $137,700 $1,539,900 $1,539,900 $101,250
Additional Green Roof Cost ($) $140,636 $490,089 $2,224,759 $132,300
Cost Increase for Green Roof (%) 102 32 144 131
Green Roof Only
DescriptionBuilding 1:
Apartment
Building 2a:
Industrial
Building 2b:
RetailBuilding 3: Office
Conventional Roof Replacement Cost ($) $137,700 $1,539,900 $1,539,900 $101,250
Additional PV + Green Roof Cost ($) $134,634 $533,554 $2,548,439 $139,833
Cost Increase for PV + Green Roof (%) 98 35 165 138
PV & Green Roof
Cost Evaluation New Construction Buildings
DescriptionBuilding 1:
Apartment
Building 2a:
Industrial
Building 2b:
RetailBuilding 3: Office
Total Building Floor Area (ft2) 50,000 150,000 150,000 300,000
Cost per ft2 ($) $139.81 $130.95 $100.00 $186.69
New Building Construction Costs ($) $6,990,500 $19,642,500 $15,000,000 $56,007,000
Additional Green Roof Cost per ft2 ($) $2.81 $3.27 $14.83 $0.44
Additional Green Roof Cost ($) $140,636 $490,089 $2,224,759 $132,300
Cost Increase for Green Roof (%) 2.0 2.5 14.8 0.2
Green Roof Only
Cost Evaluation New Construction Buildings
DescriptionBuilding 1:
Apartment
Building 2a:
Industrial
Building 2b:
RetailBuilding 3: Office
Total Building Floor Area (ft2) 50,000 150,000 150,000 300,000
Cost per ft2 ($) $139.81 $130.95 $100.00 $186.69
New Building Construction Costs ($) $6,990,500 $19,642,500 $15,000,000 $56,007,000
Additional Green Roof Cost per ft2 ($) $2.69 $3.56 $16.99 $0.47
Additional Green Roof Cost ($) $134,634 $533,554 $2,548,439 $139,833
Cost Increase for Green Roof (%) 1.9 2.7 17.0 0.2
PV & Green Roof
• This metric is used to evaluate the total life cycle costs and financial viability of different upgrade scenarios.
• Life-cycle costs includes all costs, savings, and incentives incurred during the defined analysis period.
• The NPV calculation is a method used to ‘shift’ all the identified life-cycle costs to present value.
• NPV represents the sum of all annual net cash flows minus the total initial investment costs for the analysis period presented in terms of current dollar value.
• This equation considers opportunity cost (discount rate), energy rate escalation, and the time value of money.
Cost Evaluation What is Net Present Value (NPV)?
Cost Evaluation NPV of Costs for Both Scenarios
0
500,000
1,000,000
1,500,000
2,000,000
2,500,000
3,000,000
3,500,000
Apartment Industrial Retail Office
NP
V o
f C
osts
($
)
Green Roof PV + Green Roof
Cost Evaluation
NPV of Costs & Savings for Both
Scenarios
-3,000,000
-2,500,000
-2,000,000
-1,500,000
-1,000,000
-500,000
0Apartment Industrial Retail Office
NP
V o
f C
osts
& S
avin
gs ($
)
Green Roof PV + Green Roof
Cities Comparison
Reference Cities1. San Francisco
2. Toronto
3. Chicago
4. Seattle
SAN FRANCISCOTHOUGHT
LEADERS
STORMWATER | CITY GHG EMISSIONS
WHAT? ‘Better Roofs’ Ordinance
Green roofs are one compliance option
Provides options for meeting SF Green Building Code
Leverages CA State Law requirement
INTENT Living roofs and solar energy systems are compatible and
complementary, improving the environmental benefits of each.
APPLICABILITY New Construction >2,000 ft2, <10 occupied floors
DETAILS 15%* - 30% of roof space must be solar, living roofs, or combination
EXEMPTIONS No cash-in-lieu option
RESOURCES Living Roof Manual | Interactive Map | Case Studies
IMPACT Too soon to gauge (enacted January 2017)
TORONTOTHOUGHT
LEADERS
FULL SPECTRUM ENVIRONMENTAL BENEFITS
WHAT? ‘Green Roof By-Law’
Green roofs are sole compliance option
Complements ‘Toronto Green Standard’ tiered performance measures
INTENT Full spectrum, city-wide environmental benefits
APPLICABILITY New Construction > 21,500 ft2 (2,000 m2)
New Additions > 21,500 ft2 (2,000 m2)
DETAILS Area-based requirement 20% - 60%
Cash-in-lieu approx. $20/ft2 ($200/m2)
EXEMPTIONS Area discount for solar panels, residential outdoor amenity space,
tower roof on buildings <8,000 ft2
RESOURCES Green Roof Construction Standard: Supplementary Guidelines
IMPACT 100 new green roofs in 2017
500 permits since 2010, only 40 cash-in-lieu, no code change request
CHICAGOTHOUGHT
LEADERS
STORMWATER | URBAN HEAT ISLAND
WHAT? ‘Sustainable Development Policy’
Green roofs are one compliance option
INTENT Address urban temperatures and stormwater issues in creative,
performance based ways that are equally effective
APPLICABILITY New Construction and Major Renovations receiving City funding or
special approvals (plan developments)
DETAILS Incentive-based points system comprising green roofs, green building
certifications
EXEMPTIONS None, offers multiple paths to 100pts
RESOURCES Handbook | Spreadsheet | Compliance Form
IMPACT As of 2013:
500 green roofs, 5.6 million ft2
SEATTLETHOUGHT
LEADERS
STORMWATER
WHAT? ‘Green Factor’ Regulations and Stormwater Mitigation
Green roofs are one compliance option in broader Green Building
Standard program of incentives
INTENT Increase the amount and quality of landscaping in new developments
APPLICABILITY New Construction
DETAILS Points system weighted by building zone
Combination of green roofs, rain gardens, vegetated walls, trees,
shrubs. Bonus credit for planting along the sidewalk, native plants,
food gardens
EXEMPTIONS Single-family zones, some Industrial and Downtown zones
RESOURCES Scoresheet | Landscape Standards | Tree & Plant List
IMPACT Raised the bar for quality landscaping in streetscapes and use of
landscape technologies
In most cities, green roofs are just one path to
meet the overall environmental benefit
No other cities include existing buildings
All cities engaged in lengthy outreach process
Policy context and sustainability goals must be
a key driver
CONCLUSION
Most installations are independent
of regulations, typically mission-
driven
Represents a significant O&M
investment by owner/operator
Due to external influences, difficult
to predict uptake and growth
URBAN FOOD GARDENS
Water Quality Appendix
Imperviousness Statistics for Denver
• Buildings Make Up 30% of Impervious Surfaces in Denver• Remaining 70% are roads, driveways, parking lots, and sidewalks
• Approximately 40% of Surfaces in Denver are Impervious (Includes DIA)
• Amount of Impervious Surfaces in Denver are Projected to Increase by 30% - 40% by 2040 (CU Boulder, unpublished data)
Summary of Studies – Impacts on Runoff
Authors Location Peak Flow Reduction
Average Annual Reduction in Runoff
Comments
Moran, et. al. (2004) Goldsboro, NC 78.00% 62.00% Extensive roofKinston, NC 87.00% 63.00% Extensive roof
MacMillan (2004) Toronto, ON85.00%, 82.00%, 68.00%, 46.00% 54.90%
System includes storage tank, peak flow reduction depended on storm size and decreased with larger storms
Portland Environmental Services (2013) Portland, OR 96.00% 50.00%
Portland, OR 83.00% -5.00% Site required irrigationPortland, OR 88.00% 70.00%
Speak, et. al. (2013) Manchester, UK N/A 65.70% Intensive roof
EPA (2009)University Park, PA N/A >50%
Extensive roof, almost 100% retained in summer, <20% retained in winter
Glass (2007) Washington, DC N/A 74.00%Murillo, et. al. (2016) Bogota, Columbia N/A 73.00% Studied 15 extensive roofs
EPA (2014) New York, NY N/A 37.00%-66.00%Studied four extensive roof, percent retention decreases as storm size decreases
USGS (2010) Ipswich, MA N/A >50.00%
Factors Influencing Green Roof Runoff Retention
• Storm Event Size and Intensity
• Antecedent Precipitation
• Temperature
• Green Roof Configuration• Substrate Depth
• Rooftop Slope
• Plant Coverage
• Drainage Configuration
• Orientation
• Location of Unvegetated Areas
Water Quality Impact
Green Roofs Do Not Address Primary Sources of Storm Water Pollutants in Receiving Waters
Basin Area 626 Acres
Amount of Impervious Area 502.3 Acres
Total Roof Area 168 Acres
Total Amount - Other Impervious Areas 334.3 Acres
Reduced Pollutant Load Benefit
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0
10
20
30
40
50
60
70
80
90
100
0 200 400 600 800 1000
Po
lluta
nt
Le
vel (
mg
/L)
Po
lluta
nt
Lo
ad
(m
g)
Runoff Volume (L)
Pollutant Load(mg)
Examples - Additional Water Quality Provided by Green Roofs
Site 1 Site 2
Site Description 3 acre site90% impervious80,000 sq. ft. structure40 hour drain time
10 acre site80% impervious10 – 30,000 sq. ft. structures40 hour drain time
Required Water Quality 0.1 acre-ft 0.27 acre-ft
Required Green Roof Size 0.55 acre 1.4 acre
Extra Water Quality Provided 0.015 acre-ft 0.07 acre-ft
Percent Increase in Water Quality 15% 25%
See Chapter 3, Volume 3, UDFCD for methodology to determine water quality requirements.
Water Quality Impact
Green Roofs Do Not Address Primary Sources of Storm Water Pollutants in Receiving Waters
Metric Roof Run Off Road Run Off
pH 6.07 6.9
TSS (mg/L) 47 8,500
Zinc (mg/L) 0.70 1.08
Copper (mg/L) 0.42 0.09
Lead (mg/L) 0.30 0.41
Aluminum (mg/L) 0.49 2.10
Nitrogen (mg/L) 0.02 1.74
Phosphorus
(mg/L)
0.22 0.49Results from first flush monitoringAll conventional roof types included in calculation
Average Pollutant Level in Run Off from Roofs and Roads
Factors Influencing Water Quality Results at a Site• Growing media
• Amount of organic matter
• Growing media depth / thickness
• Plantings• Presence of plants
• Plant palette
• Fertilization needs
Benefits are Conditional
• Water Quality Benefits Vary from Site to Site
• Benefits are all dependent on storm size and time since previous storms• Ability to absorb stormwater is decreased if green roof is partially or completely
saturated
Other Issues – Water Resources
• Initiative• Conflicts with Colorado water law
• Draft Rules (12/26/17)• Conflicts with Colorado water law
• Does not properly reflect administration of Colorado water law
• Provides no options for projects without an approved augmentation plan
Water Quality - Outcomes
• Add incentive – green roofs offset for water quality elsewhere on site
• Allow builders to use white roof / onsite water quality combo instead of green roof only – if goal is to reduce heat island effect and improve water quality
• Specify fee in lieu goes to funding regional water quality projects
• Add flexibility to regulations • Develop a tool, similar to the water quality scorecard that identifies needs in different
areas– water quality / quantity, heat island, etc. - and prioritize for implementation.
• Ability to monitor / identify partners and funding to do monitoring with
Air Quality Appendix
2017 South Coast Air Basin (SoCab)
2016 Montreal Increased Albedo Study
2016 Chicago UHI and Meteorology
2014 US Urbanization Scenarios on Temps in 2100
Cost Evaluation Appendix
Cost Breakdown and Net Present Value Calculation
GHG Emission Reduction for
Representative BuildingsCost Evaluation
*2016 Xcel Energy GHG Emission Factor for Colorado: 1.32 lbs eCO2/kwh (Electricity)
0.2 0.8 3.9 0.2 28.0
127.4
637.2
30.6
-
100.0
200.0
300.0
400.0
500.0
600.0
700.0
Apartment Industrial Retail Office
GH
G e
mis
sio
n re
ductio
n (to
nne
s e
CO
2) Green Roof Only
PV and Green Roof
GHG Emissions for Water Usage for
Representative BuildingsCost Evaluation
0.03
0.08
0.42
0.05
0.010.03
0.13
0.02
-
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
Apartment Industrial Retail Office
GH
G e
mis
sio
n in
cre
ase
(to
nne
s e
CO
2)
Green Roof Only
PV and Green Roof
*2016 Xcel Energy GHG Emission Factor for Colorado: 1.32 lbs eCO2/kwh (Electricity)
Source DescriptionBuilding 1:
Apartment
Building 2a:
Industrial
Building 2b:
Retail
Building 3:
Office
Roof Consultant
#1
Black roofs are assumed to be 60 mil
fully adhered EPDM Rubber or Built-up
asphalt roof (BUR). Includes structural
engineering costs.
Life Expectancy: 25 years
$154,400 $1,729,800 $1,729,800 $94,500
Roof Consultant
#2Life Expectancy: 20 years $121,000 $1,350,000 $1,350,000 $108,000
Average Capital Cost ($) $137,700 $1,539,900 $1,539,900 $101,250
Roof Consultant
#1Maintenance Costs ($) $2,200 $30,000 $30,000 $1,200
Cost Evaluation Conventional Roof Replacement Costs
Source DescriptionBuilding 1:
Apartment
Building 2a:
Industrial
Building 2b:
Retail
Building 3:
Office
Green Roof
Supplier #1
4.25in module with sedum, corners,
Installation, crane, irrigation, irrigation
installation.
$130,885 $565,341 $2,800,001 $140,550
Roof Consultant
#1
Waterproofing, drain matt, root barrier,
vegetative system, irrigation.$202,400 $471,800 N/A $126,300
Roofing
Consultant #2Does not include irrigation system. $87,384 N/A $2,304,900 $111,600
Green Roof
Supplier #2$82,500 $375,000 $1,500,000 $90,000
Average Costs ($) $125,792 $470,714 $2,201,634 $117,112
Cost per ft2 of Green Roof ($) $38 $31 $29 $33
Green Roof
Only Green Roof Only Capital Costs
Source DescriptionBuilding 1:
Apartment
Building 2a:
Industrial
Building 2b:
Retail
Building 3:
Office
Green Roof
Supplier #1Plants replacement annually, weeding $891 $1,655 $5,255 $964
Roof Consultant
#1Green roof maintenance $3,300 $45,000 $45,000 $1,800
Roof Consultant
#2Not including materials $3,690 $23,333 $23,333 $4,320
Green Roof
Supplier #2Maintenance, irrigation/water pumping $1,650 $7,500 $11,250 $1,800
Average Costs ($) $2,383 $19,372 $21,210 $2,221
Green Roof Only Maintenance CostsGreen Roof
Only
Source DescriptionBuilding 1:
Apartment
Building 2a:
Industrial
Building 2b:
Retail
Building 3:
Office
Engineering
Company #4PV Cost ($) $82,052 $372,965 $1,864,824 $89,512
Average Green
Roof Capital
Costs (prorated to
a smaller area)
Green Roof Cost ($) $37,738 $278,778 $530,753 $35,134
Average
Structural CostsStructural Engineering Costs ($) $14,844 $19,375 $23,125 $15,188
Total Capital Costs ($) $134,634 $671,118 $2,418,701 $139,833
Green Roof &
PV Costs PV & Green Roof Capital Costs
Cost of PV per ft2 of roof area covered: $36
Source DescriptionBuilding 1:
Apartment
Building 2a:
Industrial
Building 2b:
Retail
Building 3:
Office
Engineering
Company #4PV Maintenance Cost ($/year) $5,000 $7,500 $13,000 $5,000
Average Green
Roof
Maintenance
Costs (prorated to
a smaller area)
Green Roof Main. Cost ($/year) $715 $5,812 $6,363 $666
Total Maintenance Costs ($/year) $5,715 $13,312 $19,363 $5,666
PV & Green Roof Maintenance CostsGreen Roof &
PV Costs
Source DescriptionBuilding 1:
Apartment
Building 2a:
Industrial
Building 2b:
Retail
Building 3:
Office
Engineering
Company #4
Inverter Replacement
Life expectancy: 12 years$4,103 $18,648 $93,241 $4,476
Engineering
Company #4
PV Replacement
Live Expectancy: 22 years$82,052 $372,965 $1,864,824 $89,512
PV & Green Roof Replacement CostsGreen Roof &
PV Costs
DescriptionBuilding 1:
Apartment
Building 2a:
IndustrialBuilding 2b: Retail Building 3: Office
Total Capital Costs (Structural + Green Roof) $140,636 $490,089 $2,224,759 $132,300
Green Roof Maintenance Costs (NPV) $30,137 $244,989 $268,233 $28,088
Total NPV of Costs Only $170,773.10 $735,077.63 $2,492,991.63 $160,387.97
Energy Cost Savings (NPV) $432 $2,063 $10,313 $416
Total NPV of Costs and Savings -$170,341.10 -$733,014.63 -$2,482,678.63 -$159,971.97
Green Roof Only NPV CalculationGreen Roof
Only
Parameter Assumption Source
Analysis Period (years) 32 (i.e. till year 2050)
Discount Rate (%) 7 Guidelines and Discount Rates for Benefit-Cost Analysis of Federal Programs
(https://www.wbdg.org/FFC/FED/OMB/OMB-Circular-A94.pdf )
Energy Escalation Rate (%) 2 Energy Escalation Rate Calculator (https://energy.gov/eere/femp/energy-escalation-rate-
calculator-download): Colorado, 1.5% Inflation, Commercial
Electricity Blended Rate ($/kWh) 0.098 U.S. Energy Information Administration
(https://www.eia.gov/electricity/monthly/epm_table_grapher.php?t=epmt_5_6_a ): Colorado,
Commercial
DescriptionBuilding 1:
Apartment
Building 2a:
IndustrialBuilding 2b: Retail Building 3: Office
Total Capital Costs $134,634 $533,554 $2,548,439 $139,833
PV & Green Roof Maintenance Costs (NPV) $72,275 $168,351 $244,875 $71,655
PV & Inverter Replacements (NPV) $20,342 $92,463 $462,315 $22,191
Total NPV of Costs $227,251 $794,368 $3,255,629 $233,679
Energy Cost Saving (NPV) $73,737 $333,511 $1,667,570 $80,040
REC Credit (NPV) $25,015 $113,693 $568,475 $27,291
Total NPV of Savings $98,752 $447,204 $2,236,045 $107,331
Total NPV of Costs & Savings -$128,499 -$347,164 -$1,019,584 -$126,348
PV & Green Roof NPV Calculation
Parameter Assumption Source
Analysis Period (years) 32 (i.e. till year 2050)
Discount Rate (%) 7 Guidelines and Discount Rates for Benefit-Cost Analysis of Federal Programs
(https://www.wbdg.org/FFC/FED/OMB/OMB-Circular-A94.pdf )
Energy Escalation Rate (%) 2 Energy Escalation Rate Calculator (https://energy.gov/eere/femp/energy-escalation-rate-
calculator-download): Colorado, 1.5% Inflation, Commercial
Electricity Blended Rate ($/kWh) 0.098 U.S. Energy Information Administration
(https://www.eia.gov/electricity/monthly/epm_table_grapher.php?t=epmt_5_6_a ): Colorado,
Commercial
Green Roof &
PV Costs