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Strategies for sustainable construction:
Building with wood in China
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The Chinese Government values highly the culture of buildingsustainably as a national strategy, and sustainable development of
the economy and society saving energy, reducing emissions and
protecting the environment. We are trying to make environmental
protection and conservation the new engine of economic growth.
Premier Wen Jiabao, 13 November 20091
Cover images:
Glulam structure footbridge with wooddeck, Europe
Entertainment park entrance building
with shops, curved structural glulam,
Chengdu, Sichuan province
Single family wood frame community
houses, Beijing
A seismic-safe wood frame
replacement for a brick and concrete
school building destroyed in the
Sichuan earthquake
5-storey apartment building, wood
frame structure, Europe
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Introduction
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Building with Wood addresses opportunities for the further use of wood
in construction in China. It is written for the people of the Peoples
Republic of China so that they might assess and discuss these
opportunities, with full recognition of the advantages and the limitations
of wood used in construction.
Building with Wood does not pretend that wood construction offers a
panacea to solve all Chinas construction or housing requirements.Rather, it focuses on areas where wood construction can offer real
benefits to Chinese society at large and to the many individuals and
families who will need comfortable and high performance housing
within their economic means.
As the Chinese government has stated, construction requirements
in coming years will be massive. Over the next decade, an estimated
75 million multiple family housing units will be required to house
the approximately 300 million people expected to migrate into majorurban and adjacent suburban areas. And even more units will be
required to upgrade the housing stock in smaller cities and towns,
and in rural locations.Above: 8-storey wood structure apartment buildings, Europe
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Wood construction can help address these needs, and Building with
Wood explains how this can be accomplished. It points to significant
advantages for wood construction in such areas as energy savings and
total cost at both household and national levels, the inherent resistance
to earthquakes which have devastated parts of China over the last
century, and the major contributions to Chinas environmental
objectives, including potentially substantial reductions of CO2 emissions.
It addresses limitations of wood used in construction, but also and
importantly, debunks misunderstandings about building codes, costs,
fire safety, durability, land use, and deforestation.
Building with Wood is intended to add to the debate on these critical
choices facing China at this pivotal point in its amazing history. This
Introduction provides a synopsis of each of the seven chapters. In that
way, the reader can be guided to pursue his or her particular interest in
wood and wood construction, or read the book in its entirety.
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Above: 4-storey wood frame apartments, Canada
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This Chapter focuses on both the range of opportunities and the
limitations of building with wood. It notes, as well, certain advantages
over traditional construction systems in China. Wood structures are not
intended to support high rise buildings, although wood is used ascomponents in tall buildings, including infill walls, roof structures, and
other forms of hybrid construction combining concrete and steel
structures with wood.
Japan, Europe, Canada and the United States have a long tradition of
wood construction, and have developed modern wood building into
competitive solutions for the low to mid-rise segment. However, and as
noted in the Chapter, China has a much longer tradition of building with
wood than North America and most likely even longer than Europe.
This Chapter looks to the immediate as well as longer term possibilities
for wood construction in China, including exciting structural forms and
the use of engineered wood products such as glulam beams and
columns. Here, the architectural beauty and warmth of wood, which so
many Chinese have noted, is open to view and on display.
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Page 8
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This Chapter notes that China is making huge strides in addressing
environmental issues, demonstrating that it can and will lead in
contributing to international objectives. Wood construction can assist
China in making further improvements in its environmentalperformance to benefit Chinese society, and help achieve national and
international priority objectives, with no additional cost.
This Chapter explains how, noting that the use of wood in construction
reduces the impact on the environment in a number or ways. Firstly, as
explained in Chapter 3, standard wood frame buildings are substantially
more energy-efficient than standard concrete, masonry, or steel frame
buildings. This means reduced use of fossil fuels for energy, less CO2
into the atmosphere from burning those fossil fuels, and thereforereduced impact on global warming and climate change. Secondly, the
manufacture and transport of wood products not only require less
energy, but generate significantly fewer air and water pollutants. Thirdly,
wood construction provides the economic incentive to plant forests
which absorb CO2 from the air. The captured carbon makes up close to
half of the mass of the wood and is retained within the wood for the life
of the product.
The magnitude of these environmental benefits can be substantial. ThisChapter provides the details, referring to sophisticated and modern
measuring techniques, such as life cycle analysis and whole life costing.
This Chapter explains why wood buildings are more energy-efficient
than traditional forms of construction now being built in China, and how
standard wood frame buildings can be upgraded for energy performance
at very little incremental cost. It refers to studies and field tests thatprovide evidence for the order of magnitude of these savings.
This Chapter also refers to Chinese government estimates of rapid
growth in energy consumption reaching an estimated 3 billion tonnes of
coal equivalent in 2010, and growing. There are concerns about energy
shortages and the high national cost for the import of energy materials.
Reducing energy requirements is a stated national priority for China.
Because China has the largest construction volume in the world andbecause buildings in China, particularly residential buildings, consume a
large portion of national energy output, choosing wood construction over
traditional systems of construction will make a large contribution to
achieving national goals set out in Chinas Conservation Plan.
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Energyefficiency
Reducing CO2emissions andimproving theenvironment
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This Chapter addresses the cost-competitiveness of wood frame
buildings compared to concrete and steel frame buildings. It explains
why in a number of instances a wood building is less expensive to build
and to operate over the buildings life cycle. It refers to cost comparisonstudies in Europe, North America and China to provide evidence. It also
points to opportunities ahead in China for further cost reduction as
builders and designers become more familiar with wood building
practices and techniques.
The Chapter notes the predominance of wood buildings throughout the
Unites States and Canada and in regions of Europe and Japan because
they have proven cost advantages, as well as performance advantages.
In Europe particularly, new applications of wood in construction areproving to be cost-effective. These include wood roofs and wood infill
walls in concrete structures, and cross laminated timbers for the
structure of mid-rise buildings.
This Chapter explains why wood is safe, both structurally and with
respect to fire safety, and why it is durable indefinitely, providing
correct design and building practices are followed. All these areas
have been subject to extensive research involving Chinese, Europeanand Canadian scientists.
The Chapter notes that wood platform frame construction has
inherently better performance in earthquake zones. This has been
observed in investigations following severe earthquakes, including
those in the Sichuan region in 2008. The Chapter also notes that
fire safety statistics in Europe and North America show that people
are as safe in a code-compliant wood building as in a code-compliant
building constructed from concrete, masonry, or steel.
Page 46 Page 52
Safety anddurability
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Costefficiency
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This Chapter establishes the linkages between wood construction and
sustainable forestry practices, which include the importance of legal
harvesting and forest renewal. The use of wood products in construction
provides the economic base for forest renewal and sustainabledevelopment. The Chapter describes the benefits to the Chinese
economy from international trade, including trade in wood products.
Whilst the science of forestry began in Europe, and Canada leads in the
percentage of forests certified as sustainable, China leads the world in
plantation forestry. In a matter of decades, forest cover will have
increased from 6 per cent of land mass to approximately 25 per cent.
These accomplishments are truly outstanding and serve as a model for
other forestry nations.
In addition to wood construction, sustainable forest development
provides another area of common interest to strengthen relationships
between China, Europe and Canada.
This Chapter describes the framework of building codes and standards
that regulate wood products and wood construction, and clarifies any
misunderstandings that might exist in the public mind. These
regulations assure life safety, structural integrity and durability,as well as high performance in such areas as energy conservation
and sound control.
These building codes and standards are, for the most part, relatively
new to China, but are based on years of experience and research.
Chinese specialists worked closely with those from Europe and
Canada in their development. Codes continue to evolve to meet new
opportunities and requirements. The overall system of codes is
comprehensive in nature.
Page 62 Page 72
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Sustainableforestry
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Codes andstandards
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Buildingwith woodBuilding with wood has a Chinese tradition andis proven over the centuries
Wood construction offers solutions for China,including seismic performance and energyconservation
It is popular for single and multi-family housing
And suitable for commercial andpublic buildings
It is appropriate for medium-rise buildingswhich address Chinas wider housing needs
It can be used in combination withconcrete structures to improve newand existing buildings
Structural glulam, with its strong aestheticappeal, is ideal for large span construction
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Using wood in building structures is nothing new - China has been
building with wood for thousands of years. It has been used as a building
material throughout the ages wherever forests grow. And today, the
international timber trade provides countries which do not have
extensive forest resources with wood from sustainable and certified
forestry to build with.
Experience, research and product development have resulted in a rangeof effective building codes and standards.
Building with wood is becoming increasingly popular as countries
round the world seek more sustainable construction; already 70 per
cent of the housing constructed in the developed world use wood frame.
Although concrete and steel are more common construction materials
in China, the government is looking at different solutions, like wood
building, as part of its sustainability strategy. And considerable advances
have been made in the development of the codes and standards required
to ensure safety, structural integrity, and durability (see Chapter 7
Codes and standards).
Building with wood is proven over the centuries
Previous page: Re-roofing of medium-rise apartment building, downtown Beijing
Top left: Traditional Chinese wood houses, Sichuan
Top right: 4-storey wood frame apartment buildings, Canada
Above: Single family villa, wood-frame construction, Europe
Is it OK to build with wood in China? There are many
misunderstandings among consumers, developers, and policy-
making authorities. In fact, wood frame construction has a lot of
advantages. There is a rationale for most countries of the world to
build with wood It is necessary to analyze opportunities and issues
calmly and scientifically, and then move forward to fill this void in
Chinese architecture and construction.
Mr. Zhu Guangian, President, China Timber and Wood Products
Distribution Association, 2010
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Wood has many benefits as a building material. It is naturally beautiful
and widely available. Its low thermal resistance and capacity to insulate
economically provide excellent energy-efficiency. Strong and light, with
exceptional load-bearing capacity, it is easy to handle and transport. It
reduces the need for massive foundations. Fast, flexible and simple to
renovate, it is easy to work with on-site using simple tools, yet ideally
suited to factory pre-fabrication. It is available as solid wood lumber
products, graded to meet performance requirements, or can be
engineered into panels, columns and beams manufactured to meet
precise performance characteristics. Above all, it is a naturally
renewable, organic material that makes a significant contribution to
the reduction of the earths emissions of carbon dioxide.
Wood construction has major advantages in severe seismic zones
because of its light weight and natural flexibility (see Chapter 5 Safety
and durability). Pre-fabrication makes wood buildings even faster to
erect, which is another reason why they are cost-effective. And they are
built to the same code requirements and performance levels of fire
safety and durability as concrete and steel buildings. Chinese national
codes and standards (see Chapter 7 Codes and standards) have been
published to ensure appropriate design and detailing to resist potential
vulnerability to fire, microbial activity and movement due to changes
in moisture.
Wood housing, particularly multiple family units, is consistent with
Chinas land use and zoning policies. And there are different wood
construction systems appropriate for the different needs of urban,suburban and rural districts.
It has many benefits
Above: Wooden roof of Richmond Olympic Oval, Canada
It is practical to build wood frame housing, despite the high Chinese
population density. Wood frame houses are generally low-density,
because of current code restrictions on the number of storeys. As a
result, some may think it is not suitable to build low-density housing in
China, with its large population and limits on land use Japan is one of
the highest population density countries. Its population density is 2.5
times higher than China. Yet, its light wood frame construction and low-
density housing are a high proportion of total housing.
Mr. Zhu Guangian, President, China Timber and
Wood Products Distribution Association, 2010
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Wood frame construction is already being used for housing in China,
from single family dwellings in the suburbs of cities such as Shanghai
and Beijing, to low-cost rural developments where land availability is
not a problem. They have proved cost-competitive and perform well in
comparison with concrete and steel frame housing.
But much more can be done. Wood construction is the solution to other
building requirements in China as well. These include medium-density
multi-storey apartments, small commercial and office buildings,
schools, medical clinics, nursing homes, universities and research
centres, sports arenas and other recreational facilities.
Wood frame construction: low-rise solutions
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Above: Single family wood frame community, Beijing
Right: Semi-detached wood frame house, Sichuan
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Wood can make a contribution to solving Chinas housing shortages
through high density multi-family solutions. While these can take
the form of two or three-storey apartment blocks, the future liesin the higher-rise buildings which are well-proven in Europe and
North America.
They have gained popularity in these regions because of lower building
costs, woods suitability for highly efficient industrial building methods,
better energy-efficiency, better seismic performance and a growing
environmental awareness. And, because of their low weight, multi-
storey wood buildings can be constructed without the need for extensive
pile foundations. This makes it possible to develop sites which wouldpreviously have been impractical.
In China, as of 2009, existing fire codes do not allow wood frame
apartment blocks of four or more storeys. However, this may be an
option for the future, as these codes are often under review and the
scientific experience supports more storeys.
Wood frame construction:medium-rise solutions
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Above and right: 5-storey wood frame apartment building, Europe
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At present, wood frame is used for single family and multi-family homes
of two or three storeys in China. Wood members form a structural
framework which is sheathed with structural wood panels. Foundations
are generally concrete. The floor above can be either wood or a concrete
slab and forms the platform for the next storey. Roof and wall insulation
and water-proof membranes provide energy-efficiency and protection
from moisture. Interiors are usually dry-lined with fire-resistant gypsum
board, and many different materials can be used for external cladding.
Because the structure has multiple wood members, panels, fasteners
and connectors, loads can be carried through a number of alternative
pathways. As a result, wood frame buildings are highly resistant to
sudden failure in earthquakes or high winds.
Wood frame in China
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Above: Multiple living-unit wood frame construction, Sichuan
Left: A typical wall assembly for wood frame construction
Facing page: Multiple living-unit wood frame construction, Sichuan
Sheathing board
Sheathing membrane
Preservative treated
vertical strapping
Rain screen drainagecavity opening
Paper backed lath
Stucco
Perforated casing bead
Insect screen overcavity opening
Metal flashing
Gypsum wall board
Insulation
Wood framing
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Multi-family units are built using the same techniques and under the
same building codes as single family units, and are separated by code-
required fire-rated assemblies. The units generally range in size from100 to 300 square meters.
Multi-storey wood frame buildings are popular in many countries.
Where five and six-storey blocks are now being built, apartments
are generally on a single storey, separated from each other by
fire resistant assemblies. Horizontal stability in these taller buildings
is achieved using engineering design which incorporates bracedwalls and heavy-duty metal connections between assemblies.
Noise is an important consideration, too. Effective solutions are
available to limit sound transmission through floors and walls.
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Hybrid construction: wood frame storeys on concrete structure
Hybrid construction, where wood construction is combined with
concrete and/or steel, is a promising opportunity for the future of China.
This includes the construction of buildings which have the lower storeyor storeys (or parkade) in concrete, to which a light-weight energy-
efficient wood super-structure can be attached.
In Europe and North America, wood frame buildings of up to six or
seven storeys are achieved using a concrete lower storey. And in China,
buildings of up to three wood frame storeys on top of up to four concrete
storeys may soon be accepted.
These hybrids can combine commercial space, such as stores andoffices, in the concrete portion of the building, with housing in the wood
frame part. In some settings, hybrids may be the most practical,
efficient, and cost-effective option.
Left: Light-weight wood frame storeys on multi-storey concrete building, Europe
Above: Multi-family wood frame apartment building on concrete parkade, Canada
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Chinese fire safety codes allow the use of infill wood frame exterior
walls in concrete structures up to six storeys, soon likely to be extended
to seven storeys high for residential, offices, and certain factories and
warehouses. These structures have been built cost-competitively at up
to twenty storeys in northern Europe for a number of years, where
increasingly stringent energy-efficiency requirements are a key driver.
Exterior infill walls are light, as they are designed to take only the load
of their weight and the wind and seismic loads that directly affect them.
They can be pre-fabricated in a factory or built on-site and have verygood insulation characteristics in relation to their thickness, providing
substantially better energy performance than traditional concrete,
masonry or steel construction.
Where wood frame is used for interior walls in concrete and steel
structures as partitions, it provides flexibility of design, including floor
layout, fire safety, sound insulation and renovation. Wood infill partitions
are non-structural, lightweight, and are suitable for a range of interior
finishes. They can also be designed to meet the fire and sound
requirements for apartment partition walls. Wood frame partitions are
approved up to eighteen stories.
Hybrid construction: wood frame walls in concrete structures
Top left: High-rise apartment building using wood frame infill wall panels, Europe
Above: Assembling pre-fabricated wood frame exterior infill wall panels in amulti-storey concrete structure building, Europe
The main benefits of exterior wood infill walls:
Outstanding thermal properties and energy conservation
Reduced wall thickness maximizes usable living space
by a typical 2 per cent
Shorter on-site construction time through pre-fabrication
Reduced foundation load
Improved seismic performance
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Many of the typically concrete medium-rise residential buildings
throughout China have flat roofs that tend to leak and are poorly
insulated for energy conservation and thermal comfort. These existing
roofs can be covered with a pitched wood frame truss roof. This is a
cost-effective way of keeping the rain out, improving the look of the
building and, with additional insulation in the roof cavity, reducing
energy costs. It is also an effective way of delivering a thermally
comfortable attic space for extra accommodation, or of installing
mechanical systems for heating, cooling, and ventilation.
This system is as competitive for installing roof systems on new
concrete structures as for replacing old concrete roof systems.
Hybrid construction: wood frame roofs on concrete structures
Above: Re-roofed apartment buildings with habitable attic, downtown Beijing
Top right: Attic living space, downtown Beijing
Centre right: Installing thermal insulation in wood frame attic living space
Right: Re-roofed apartment buildings, Xu Hui district, Shanghai
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Engineered wood construction: solid wood panels
Solid wood panel structures provide a leading-edge alternative for
six to ten-storey buildings. Although the technology is relatively new
and not yet recognized in Chinese codes, it is widely used across
Europe. The tallest built so far is a nine-storey residential building in
London, England.
Cross-laminated boards are glued together and used to build walls and
joists. Panels are machined in a factory to fine tolerances by computer-
controlled equipment. The panels arrive on site with apertures for doors
and windows, and wiring and plumbing channels already prepared. The
walls can be insulated to provide a high level of energy-efficiency.
Superior load-carrying characteristics, including lateral stability against
wind and seismic forces, as well as excellent fire safety performance,
make cross laminated timbers suitable for medium and even high-rise
buildings. And the amount of timber used means buildings made with
solid wood panels are highly effective carbon stores.
These environmentally-friendly solid wood buildings offer
longer-term opportunities in China, particularly for high density
housing requirements.
Top left: Assembling solid wood panels in multi-storeyapartment building, Europe
Above: 9-storey apartment building with solid wood panelstructure, Europe
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Engineered wood construction: glued laminated timber (glulam)
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In North America and Europe, structural glue laminated timber is widely
used in constructions where span width is an issue and/or the unique
beauty of the wood is to be exploited architecturally. Glulam beams andcolumns have a strong aesthetic appeal, as the structure of a building
can be expressed in the exposed beauty of the wood.
Glue laminated timber engineered wood beams and columns - are
used in homes, schools, sports halls, railway stations, industrial and
commercial buildings, such as shopping centres and expo buildings,
and public buildings, such as museums and concert halls. They are
also used in landscaping and infrastructure applications such as
glulam bridges.
Glulam beams and columns come as standard products, with a variety
of cross-sections and lengths. Custom designed beams and columns
are pre-fabricated according to customer needs and can include curved
shapes and mechanical interfaces to concrete or steel structures etc.
Glulam is a mature technology in Europe, where large span buildings
are still in use after almost 100 years. Modern design methods are
available and national codes design, production, fire - supportingglulam construction in China are to be approved in 2010.
Facing page, top: Entertainment park entrance building in curved structuralglulam, Chengdu, Sichuan province
Facing page, left: Glulam and wood truss shopping mall, Europe
Facing page, right: Swimming pool with structural glulam roof, Beijing
Top right: Entrance to Swedish pavilion in structural glulam,World Expo 2010, Shanghai
Bottom right: New temple with glulam post and beam structure, Zhejiang
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Landscaping
Top: Heavy duty structural glulam road bridge, Europe
Right: Western red cedar landscaping, Canada
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Wood products, treated with the latest environmentally-friendly
preservatives, or using naturally durable wood such as China fir,Western red cedar, or yellow cedar, are used extensively for
landscaping. Whether decking, pathways, fences, retaining walls, or
small structures like storage sheds and gazebos, wood products fit
naturally into many urban and suburban environments, parks and
other recreational projects.
Above: Wood landscaping, Guangzhou
Below left: Wood decking and seating, Pudong, Shanghai
Below right: Glulam structural arch footbridge with wood decking, Shanghai
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The traditional way to construct wood frame buildings in North America
is on-site, particularly when there is labour availability. In Europe, wood
frame assemblies are typically pre-fabricated. Engineered wood
construction, such as glulam, is most commonly erected piece by piece
on-site. In China, almost all wood buildings are currently constructed
on-site. Building materials and structural components are freighted to
the building site and the various assemblies walls, floors, etc. are
framed on-site. The method requires organization and planning on the
building site and measures must be taken to avoid moisture damage tomaterials. On-site construction relies on a skilled work force and, while
much faster than using other materials, is slower than using pre-
fabricated elements.
On-site construction does not require the initial capital costs for plant
and machinery, nor the need to maintain capacity utilization. It is
particularly appropriate where housing volumes are not large, where
labour is reasonably priced and plentiful, and where flexibility and low
overheads are important.
While more capital-intensive, off-site pre-fabrication has the benefit of
controlled factory conditions, less dependence on on-site labour and
faster construction times.
In the case of wood frame construction, only a few days on the buildingsite are needed to assemble a water-tight structure, complete with roof.
The panels can be pre-fabricated with insulation, windows and doors.
Entire units can even be made complete with electricity, water and
waste pipes, kitchens and wet rooms, floors and papered walls.
Wood construction: on-site or prefabrication
Above: On-site construction of new roof on existing apartment building, Beijing
Facing page, left: Pre-fabrication of wood panels, including installation of services
Facing page, right: Production line for pre-fabrication of wood panels
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Pre-fabricated components are relatively light and can be erected
at heights of several storeys using simple lifting equipment,
such as the cranes on the trucks that deliver components to
site. Components may need protection against the elements
to prevent dampness.
The extent of pre-fabrication varies widely between countries and
companies, depending on economic factors. It does require an
up-front investment in plant and equipment which could impose
an uncompetitive burden. While this is essentially the case in
China at present, over the longer term, pre-fabrication may
prove advantageous.
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2
Reducing CO2emissions and
improving the
environmentWood products store the CO2 absorbed bygrowing trees
Substantial reductions of CO2 emissions
can be achieved by substituting wood forother materials
Wood buildings also reduce CO2 emissionsas a result of their energy-efficiency
Life Cycle Assessment demonstrates the lowenvironmental impact of wood buildings
Whole Life Costing demonstrates the cost-efficiency of wood buildings
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Growing trees absorb CO
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Wood is an extraordinary natural resource. It provides a high-
performance building material without depleting the earths resources.
It grows in forests and plantations which clean the air, creating the
conditions that make the planet habitable, while providing a natural
habitat for leisure and wildlife.
On average, trees absorb one
tonne of CO2
and release
almost three-quarters of a
tonne of oxygen for every
cubic metres growth. The CO2
is stored in the wood as
carbon. Young, active trees
replace the mature trees,
absorbing yet more CO2.
Above: Growing trees absorb carbon dioxide and release oxygen2
Growing trees absorb CO2
Wood plays a major role in
combating climate change.
Trees reduce CO2
in the atmosphere,
since one cubic metre of wood
absorbs around one tonne of CO2.
Greater use of wood in construction
can reduce greenhouse gas
emissions by stimulating the
expansion of Chinas forests and by
reducing requirements for fossil
fuel-intensive products.
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Coping with climate change should be a major strategy fornational economic and social development There should be
greater public awareness in addressing global climate change
and encouraging low-carbon life styles and consumption.
State Council, Press Statement, 27 November, 2009
Wood products store CO2
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Throughout their life, wood products continue to store the carbon
sequestered by the harvested trees. Further CO2 gains can be achievedby extending the life of the wood product, by recycling into panel
products, and by recovering the energy in the wood at the end of its life
by using it as a biomass fuel.
Managing a forest sustainably means ensuring new trees replace the
harvested trees. So the forest maintains its carbon store. And theamount of carbon stored in the product made from the harvested wood
is a net gain. This means the wood can be described as carbon
negative it stores more carbon than the equivalent CO2 it emits from
the harvesting, processing, transport and fabrication. This helps reduce
the growth of CO2 in the atmosphere, slowing down climate change.
Wood products store CO2
Since wood products store the carbon initially trapped in trees,
carbon is removed from the atmosphere for as long as the wood
product remains in use, and beyond, when the product is re-used
or recycled for secondary material or energy recovery.
European Commissions DG Enterprise3
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China is going to reduce the intensity of carbon dioxide emissions
per unit of GDP in 2020 by 40 to 45 per cent compared with the
level of 2005 Appropriate handling of the climate change issue is
of vital interest to China's social and economic development and
people's fundamental interests, as well as the welfare of all the
people in the world and the world's long-term development.
State Council, Press Statement, 27 November 2009
Substituting wood for other materials reduces CO2 emissions
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Using wood in construction is a good thing in itself. Its effects are
even more positive when the CO2 savings made by not using other
construction materials are taken into account.
Wood has lower CO2 emissions than any other building material.
The wood industry is also one of the biggest users of biomass energy,
often contributing excess energy to national grid networks. Even the
recycling of materials such as steel and aluminium, whilst a necessary
part of modern materials production, requires large energy inputscompared with wood.
CO2 emissions will vary by
country, according to the
predominant energy source.
Chinas energy production is
heavily dependent on coal,
which produces high levels
of CO2 emissions.
Substituting wood for other materials reduces CO2 emissions
Substituting a cubic metre of wood
for other construction materials
(concrete, blocks or bricks) results
in an average saving of 0.7 to 1.1
tonne of CO2.2
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The index of carbon dioxide emissions cuts, announced for the
first time by China, would be a binding goal to be
incorporated into China's medium and long-term national
social and economic development plans Given the country's
huge population, prominent economic structural problems,
coal-dominated energy consumption structure, and increasing
demand for energy, the government needs to make strenuous
efforts to realize those targets.
State Council, Press Statement, 27 November 2009
Lumber (kiln dried)
Steel girders
Concrete columnsand beams
Injectionmoulded PVC
Roofing tiles
-1,000 -500 0 500 1,000 1,500 2,000 2,500
Kilograms CO2 per tonne
Above: Cradle to gate carbon footprints for materials used in construction,Edinburgh Centre for Carbon Management2
Wood buildings have lower CO2
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Saving CO2 emissions from the construction phase is just one part of
the story. At the moment around two-thirds of a buildings CO2emissions come from the in-use phase. Because of woods naturally
low thermal conductivity and the capacity for low cost, effective
insulation, wood construction provides a competitive way to achieve
higher energy-efficiency. As the walls do not have to be so thick to
achieve good insulation, houses built using wood have more livable
space (see Chapter 3 Energy-efficiency).
g 2emissions throughout their lifetime
Besides, the more wood products replace other materials, themore the so-called substitution effect further reduces CO2 in
the atmosphere.
European Commissions DG Enterprise3
31
Right: Zero carbon demonstration house, Europe
Below: Wood frame apartment building, Europe
Life Cycle Assessment shows wood building elements have lower impacts
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Governments world-wide are increasingly concerned about issues like
recycling, waste disposal, and the environmental impacts of materials
production, as well as energy emissions. As a result, buildingregulations internationally are requiring that principles of sustainable
development apply to construction. In some cases these standards are
mandatory. This has led to demands for materials and products to be
assessed over a complete life cycle.
Life Cycle Assessment (LCA) is a tool which assesses the environmental
impacts of a building component right the way through its lifecycle in
three phases:
It helps designers, clients, specifiers and developers understand the full
environmental impact of the materials they choose. It gives them the
information they need to choose materials which will contribute towards
more sustainable buildings.
32
y g p
LCA has been widely used to compare the
environmental impacts of building materials such as
wood, steel and concrete, and scientists world-wide
have come to the same conclusion: compared to the
alternatives, wood buildings produce less air and water
pollution, require less energy across their life cycle, and
generate lower CO2 emissions.
Left: Wood frame structure apartment building, Europe
Production phase
Extraction
Production
Transport to site
Construction
In-use phase
Energy use
Thermal properties
Maintenance
End-of-life phase
Recycling
Recovery
Disposal
Whole Life Costing shows how competitive wood solutions can be
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Whole Life Costing (WLC) is a commonly used technique which assesses
the cost of a product or project over a specific period of time. It takes
into account all relevant financial factors from the initial capital costs,
through future operational costs, to disposal.
WLC, together with LCA, can provide a thorough economic and
environmental assessment to support decision-making and an effective
procurement strategy.
g
Right: Glulam construction for rapid transit system, Canada
Below: 8-storey apartment building, glued solid wood structure, Europe
Case studies of the CO2 emissions savings to be made by using wood
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Example 1: A solid wood panel school building
The more wood used in a building, the lower its carbon footprint. This
school uses solid timber as its primary structure to achieve a negative
materials footprint of -40.9 tonnes of CO2.4
Example 2: Two multi-storey apartment blocks
Research in Sweden in 2007 compared the CO2 balances for two four-
storey buildings, one with a timber frame and the other with a concrete
frame, over a 100-year period.5
The study researched the entire construction process from cradle to
grave. A 4-storey wood framed building with 16 apartments (1,190 m2
area) was compared with a similar concrete frame construction. The
concrete frame building showed emissions of around 96 tonnes of CO2,
while the timber frame building showed no emissions - instead it
showed a net uptake of 150 tonnes of CO2.
- The construction of the building with the wooden frame
required less energy
- Wood waste from the construction process could be
recycled and used as an alternative to fossil fuels
- Carbon from CO2 emissions is stored in the wood
- Concrete production has significant CO2 emissions
- The more wood used to replace steel and concrete,
the better for the climate.
34
Above: Low carbon demonstration school building using solid woodpanel construction
Facing page left: The wood frame apartment building in the Swedish carbondioxide comparison study
Facing page right: A low carbon apartment building under construction usingsolid wood panels, Europe
Emissions of around 96 tonnes of CO2 from the concrete buildingcompared with a net uptake of 150 tonnes of CO2 from the timberframe building
Wood frame building Concrete building
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Example 3: A solid wood panel multi-storey apartment block
This apartment building in London has a solid wood structure. It was
pre-fabricated offsite using laminated panels up to 12.5m long, 2.9m
wide and 170mm thick, produced from sawmill offcuts.
The glue content of the panels is 2 per cent and the building uses 360m3
of lumber, saving around 400 tonnes of CO2 emissions compared with a
concrete and steel construction.4
35
LCA case studies
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36
Example 1: Wood versus steel, and wood versus concrete, a study
of single family homes in the USA6
A study by the Athena Institute, Canada, looked at the environmental
impacts of wood compared with steel and concrete in single family
homes in Minnesota and Atlanta, USA. Results showed considerable
benefits for wood construction in both instances, across a range
of environmental impacts, including air and water pollution and
solid waste.
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Embodiedenergy (Gj)
Global warmingpotential Equiv.
CO2 (kg)
Air pollution(index)
Water pollution
(index)
Solid wastes (kg)
Embodied
energy (Gj)
Global warmingpotential Equiv.
CO2 (kg)
Air pollution(index)
Water pollution
(index)
Solid wastes (kg)
0 1 2 3 4 5 6 7 8 9 10
Wood
Steel
Wood
Concrete
Environmental impacts of wood house vs steel house
Environmental impacts of wood house vs concrete house
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Example 2: A comparison of wood, steel and concrete apartment
construction in China7
A study carried out by Beijing University of Technology (BJUT) compared
the life cycle performance of similar wood, steel and concrete
apartment buildings over a 50-year service life. The study focused on
the production and in-use phases. The LCA considered all energy and
material flows from the environment, as well as emissions to air, water
and ground from the three building designs.
The findings showed the wood frame construction was about 25 per cent
more energy-efficient than either the steel or concrete frame designs
across the overall life cycle. They demonstrated the importance of the
energy embodied in materials (the production phase), even compared
with the long-term operating energy consumption. And they highlighted
the importance of improving building insulation levels, air tightness and
other energy conservation measures.
Example 3: An exploratory study of Energy Use and Environmental
Impacts of Wood Frame Structures Relative to Other Structures
in China8
A second study compared the environmental impacts of three different
construction systems, wood frame, steel frame and concrete frame,
using three houses of the same footprint (223m2) and total floor area
(607.8m2). To simplify the data, the study considered the impacts of six
main building materials within each house: cement, steel, timber,
glazing, OSB and I-joists.
From the table it can be clearly seen that the wood frame construction
produces the least damage to the ecosystem, and consumes the least
resources (except for timber, which is, of course, renewable).
Embodiedmaterials
Construction
Use andOperation
WholeLife Cycle
Woodstructure
Steelstructure
Concrete
structure
Wood Frame Construction
Steel Frame Construction
Concrete Frame Construction
Ecosystem damage
Resource consumption
Total
The energy consumption for each phase and life cycle ofthree types of building
Ecosystem damage and resource consumption
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Energy-efficiencyChina needs increasing energy supplies
But most energy production has an impacton the environment
Energy-efficient buildings are part ofthe answer
Wood buildings are more energy-efficient
Wood frame buildings are easier to insulate
Research confirms wood buildings save energy
They outperform Chinese energy codes
And reduce the cost of meeting the codes339
China is facing an energy challenge
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China is experiencing rapid economic development. It has the worlds
second largest energy consumption, exceeded only by the USA. In 2003
its total energy consumption was 1.68 billion tonnes coal equivalent. By
2010, according to a recent government estimate, energy consumption
could exceed 3 billion tonnes a year.9
This growth in consumption has led to energy shortages, which can hold
back economic development. And, in spite of extensive domestic fossil
fuel reserves, China has become one of the largest energy importers in
the world.
Improving energy-efficiency and developing renewable energy supplies
have therefore become a priority.
Energy production has a serious impact on the environment
Chinas current energy supplies are heavily dependent on fossil fuels,
which emit large quantities of CO2. Rapid economic development,
accompanied by higher energy consumption and the use of fossil
fuels, is presenting serious challenges to air and water quality
across the country.
Improving energy conservation and using environmentally friendly and
renewable materials can reduce the impact of economic development
and provide a better living environment for Chinas population.
Left: Energy-efficient wood frame infill wall installation in a concretestructure building
Facing page: Energy-efficient wood frame ski lodges, Xiliang mountain, Sichuan
The energy consumption of buildings takes about 28 per cent
of the total energy consumption in China, but it is expected toincrease in the coming years. However, most urban buildings
are expected to be retrofitted by 2020 in order to improve
energy efficiency.
Deputy Minister Qiu Baoxing, Ministry of
Housing and Urban Rural Development11
It is important for fast growing economies to promote energy
savings in new building development and green buildings,
and to renovate existing buildings using green and energy-saving technologies.
Deputy Minister Qiu Baoxing, Ministry of
Housing and Urban-Rural Development10
Energy-efficient buildings are vital to Chinas development
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The construction and operation of buildings create greater
environmental impacts than most people realize. Globally, buildings are
responsible for 20 per cent of all water consumption, 25 to 40 per cent
of all energy use, 30 to 40 per cent of greenhouse gas emissions and 30to 40 per cent of solid waste generation. 12
Estimates suggests that the building sector now accounts for about
one-third of Chinas total energy use, and this is expected to grow in
the future.13
The residential sector accounts for about 38 per cent of total building
energy use, a proportion that is likely to continue to rise along with
increasing affluence and urbanisation.14
It is important to consider the scale of Chinas construction and the pace
of change. China has the largest construction volume in the world.
Almost two billion square metres of new buildings are completed each
year. Although more than 80 per cent of buildings are categorized as
energy-inefficient, with energy consumption per unit area currently two
to three times higher than in developed countries, China has set
ambitious targets and will work hard to achieve them.15
According to Jiang Yi, professor in architecture at Tsinghua University,
energy use in the building sector will double by 2020 if no serious
action is taken.15
Using wood in buildings is an important step towards meeting
these demands.
Global construction spending 2007 (US$bn)16
Global construction spending growth 2008 (% change)16
0 200 400 600 800 1000
USA
Japan
China
Germany
Italy
France
UK
Brazil
Spain
Korea
Mexico
Australia
India
Other
-2 0 2 4 6 8 10
USA
Japan
China
Germany
Italy
France
UK
Brazil
Spain
Korea
MexicoAustralia
India
Other
The government has implemented energy-efficiency measures
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There are two sets of national building energy standards in China,
one for public buildings and another for residential buildings. Both
standards are set as mandatory by MOC, and China is addressing the
challenges of enforcement. In 2005, MOHURD (the Ministry of Housing
and Urban-Rural Development) began a building inspection programme
to monitor the implementation of building energy-efficiency. Under
this programme, design institutions, developers and construction
companies will lose their licenses or certificates if they do not comply
with the regulations.
In November 2004, the National Development and Reform Commission
(NDRC) issued the China Medium and Long Term Energy Conservation
Plan (Conservation Plan), which stressed energy conservation as the key
principle for sustainable socio-economic development in China and an
urgent issue to address. In the Conservation Plan, energy saving targets
for buildings have been emphasized:
- During the Eleventh Five-year Plan period, new buildings should be
subject to a strict 50 per cent energy-saving design standard. Several
major cities, such as Beijing and Tianjin will go further, implementing
a 65 per cent energy-saving standard
- Existing residential and public buildings will be subject to energy-
saving retrofit measures as part of urban reconstruction. Large cities
are expected to improve 25 per cent of building areas, medium cities
15 per cent and small cities 10 per cent.
Top: Wood construction office building, Shanghai
Wood buildings are more energy-efficient
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Wood construction consumes minimal energy. Wood is light and easy to
put together on site. Foundations are minimized. Transport requires less
energy. And wood construction is quick, requiring little or no use of
heavy-duty equipment.
Wood is a good thermal insulator. It is 400 times better at resisting
thermal conductivity than steel, and 10 times better than concrete or
bricks. This means extra insulation or thicker walls are required for
steel, concrete, or masonry structures to achieve the same level of
thermal resistance.
Tsinghua University investigated the energy conservation
performance of wood construction using standard building
techniques with comparable concrete and steel
construction. The wood buildings generally out-performed
both concrete and steel.
Professor Lin Borong, Tsinghua University, March 2010
Above: Wood frame construction provides thermal comfort
Right: Thermal insulation in the cavities of an exterior wood frame wall reduceswall thickness and maximises usable living space by two to five per cent
Wood frame buildings are easy to insulate thermally
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Unlike solid concrete or masonry structures, wood frame walls, floor
joists, and roof joists inherently provide space for fibrous insulation, the
most economical way to achieve better insulation. Application of mineral
insulation is a standard element of any wood construction project. It is
conducted with minimal additional labour or material expense and
provides significant returns. Woods low thermal conductivity means 90per cent of the insulation value can be realized, with only 10 per cent
lost to thermal bridging. Wood structures can also be readily insulated
on the exterior or interior if additional energy savings are desired.
Light steel frame walls also have cavities for insulation. But the high
thermal conductivity of steel means only 50 per cent of the insulation
value can be achieved. Extra measures are always required to reduce
local energy loss and vapour condensation as a result of steel thermal
bridging. It can also lead to ghost marks; dark vertical marks thatappear over the framing on the interior surfaces of exterior walls, as a
result of faster dust accumulation on cool surfaces.
An energy consumption field test by the Harbin Institute of
Technology considered a wood building using 38 mm x 140 mm
studs, cavity insulation and 30 mm of exterior rigid panel polystyrene
insulation. This was compared with a brick building clad with 60 mm
rigid panel polystyrene insulation. Harbin is an area which experiences
severe cold.17
The test measured the thermal transfer coefficients (K) of the walls
as 0.244 for wood buildings and 0.526 for brick buildings. The timber
building reduced coal consumption by about 50 per cent.
Above: Insulation is simple to fit in wood buildings
Facing page: Infra-red temperature imaging of exterior wall
Field tests in China confirm wood buildings save energy
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Wood frame construction outperforms Chinese Energy Codes with no
additional cost
Wood frame buildings are generally rated as more efficient and
economical than other construction types. They outperform all the
relevant requirements for building energy efficiency in China with no
additional cost.
JGJ 26 Standards for Energy Design for Severe Cold and Cold Areas
requires buildings in Beijing to have thermal transfer coefficients (K)
from 0.55 to 1.16. Typical wood frame walls can achieve thermal transfer
coefficients from 0.3 to 0.5 depending on stud size, spacing and
insulation materials.
According to calculations by Shanghai Xiandai Architectural Design
Group, the effective thermal transfer coefficients of conventional
wall assemblies with 38 mm x 89 mm studs, range from 0.46-0.49
and 0.37-0.40 with rock wool and glass fibre insulation, taking into
account the thermal conductivity of the studs. These thermal transfer
coefficients (K) can be further reduced to 0.3 or lower if 38 mm x 140
mm or wider studs are used for framing, or extra exterior insulation is
applied. By comparison, steel, concrete, or brick walls would requireextra and more expensive, rigid insulation panels in order to achieve
similar insulation performance, and walls would be thicker.
The energy-efficiency of wood construction reduces the cost of
meeting the codes
All concrete, masonry, and steel frame structures need rigid insulation
panels in order to meet Chinas energy efficiency requirements. In
Beijing, concrete or masonry buildings need additional 50 mm to 80 mm
thick insulating panels. In Shanghai, they need 50 mm thick panels in
order to meet the minimum energy requirements. By comparison,
conventional wood frame construction using fibre insulation meets the
requirements without additional insulation, using 38 x140 mm studs inBeijing and 38 x 89 mm studs in Shanghai. A considerable saving can
therefore be made.
If additional insulation is not used, steel and concrete buildings will
consume much more heating and cooling energy. The savings in cooling
and heating costs of wood frame building envelopes have been
confirmed and praised by developers and property managers who have
experience with these constructions in China. As one of the worlds
largest countries, China is subject to extreme climate variations. Theenergy-efficiency of wood structures is beneficial in all climates, but
particularly in Chinas colder regions, where heating is required.
Thermal conductivityis the rate of heat transferred by conduction through solid materials
subject to a temperature difference on each side of the material.
Thermal transfer coefficient(U-value or K-coefficient) is a measure of heat conductivity
through a building assembly, comprising a number of materials.
Thermal resistance(RSI) refers to the resistance to conductive heat transfer through a
material or assembly. It is the reciprocal of conductivity (1/K).
A lower Kor a higher RSI means better thermal or insulating performance.
Thermal bridgingrefers to the higher thermal conductivity of a structural component,
within the insulated assembly, providing a bridge for more rapid heat transfer through the
assembly and thereby reducing the overall thermal performance of the assembly.
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Cost-efficiencyWood frame is popular world-wide
There are many studies showing it is cost-
efficient in construction and operation
Studies in China show it can be cost-effective
across many segments, including commercial,
recreational, and residential
Particularly when high energy-efficiency andseismic safety are required
As building with wood becomes more popular
in China, costs will become even more
competitive4
The most popular system in the developed world
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It is never easy to compare the costs of building with different materials
and systems. So many factors are involved. For example, the relative
costs of different materials change according to supply and demand as
well as currency fluctuations. Local conditions vary significantly. And
there are many different ways to build in different materials. Building
with wood could involve anything from traditional wood frame, to
technologically advanced engineered systems, or even hybrid
construction. And building efficiencies vary, depending on the regulatory
system, scale of development, knowledge and skills, the extent of off-
site construction, and how adept and experienced the construction
company is at planning and managing the building process.
It is worth noting, however, that wood frame systems account for around
70 per cent of residential construction in the developed world. And 90
per cent in North America. One of the reasons for its popularity is its
cost-effectiveness, which includes a much shorter construction time and
less waste than other systems.
48
Wood frame construction (WFC) products and components are
manufactured in a factory, which means higher construction
efficiency, shorter construction period, lower cost, quicker
capital turnover. It takes around 100 days to build a 300 m2
single family residence with WFC, while a concrete building
needs around 145 days. Also, wood houses are light. The dead
weight of WFC walls is only about 1/10 of concrete walls, and
the dead weight of WFC floors and roofs is about 1/8 of the
concrete ones. So WFC has much lower requirements on
foundations, which is cost-saving.
Mr. Zhu Guangqian, President, China Timber and
Wood Products Distribution Association, 2010
Cost-competitive world-wide
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International comparisons show cost advantages for building with wood
over concrete and steel for many types of residential and commercial
buildings. These demonstrate the potential for cost savings in China
from building with wood, recognizing that modern wood construction in
China is new and full economies have yet to be realized.
One study, carried out in South Carolina, USA, showed wood frame
houses saving 14 per cent in construction costs compared with
identical steel frame houses.18
A recent cost study comparing wood and concrete for the construction
of a three-storey motel building in the United States demonstrates
that using wood can achieve a saving of 7-9 per cent in material
costs alone.19
Experiences in Europe demonstrate that wood construction can cut
costs substantially, depending on design and application. If off-site
pre-fabrication is used, construction time can be reduced by as much
as two-thirds, compared with other construction types.
Even in areas like Taiwan, where wood frame construction is still
relatively new, it has been shown by local design professionals that
wood construction can be cost-competitive with concrete buildings.
Wood roofs were shown to be less expensive than concrete roofs.20
As wood is a better thermal insulator than other structural materials,
wood frame buildings reach the high insulation standards increasingly
demanded by governments world-wide more easily.
There is also the additional benefit of a two to five per cent increase inliving space, as the wood frame walls can achieve excellent insulation
values with a substantially thinner cross-section than other materials.
This is a significant cost advantage on the basis of liveable space, which
is generally not taken into account in standard cost comparisons.
Research in the United Kingdom shows that wood frame construction
becomes even more cost-competitive when higher energy-efficiency
building envelopes are required.21
Above: 6-storey wood construction apartment buildings, Europe
Facing page: Wood frame apartment building, Canada
90 95 100 105 110 115
Cost comparison between wood and concrete construction
for three-storey buildings in the USA19
Concrete Wood
Cost-competitive in China
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Although modern wood construction is new to China, with full cost
savings yet to be realized, in-depth research shows that wood frame
construction is competitive depending on its application.
For example, a cost comparison study was conducted in China looking
at identical building designs constructed with different structural
materials. The results showed the construction costs of wood frame
houses without living space in the lofts were lower than for concrete
or masonry. In particular, materials and cost savings could be made in
the foundations. When living spaces were built into the lofts, the cost
of wood frame could be higher. But when comparisons are made per
square metre of living space, they still work out cheaper to build than
comparable concrete houses.
The study also demonstrated that wood roofs can be cost-competitive
with concrete roofs, as well as having better thermal, seismic and
occupant comfort performance.
Wood frame houses are promising for rural areas
Research has shown that small-scale rural wood frame houses can
be built for about 1000 RMB per square metre.22 This is affordable for a
large percentage of the population in rural China. Construction of such a
new building system to replace traditional masonry and concrete houses
would improve occupant comfort, thermal performance and seismic
safety. It would be an important signal of improved living standards for
Chinas large rural population.
Wood infill walls could revolutionize high-rise construction
European experiences with non-load-bearing wood infill walls in
concrete high-rise buildings suggest they would be cost-competitive
in China. Combining wood with concrete could revolutionize high-rise
construction in China, with cost advantages, lighter weight, better
thermal and seismic performance, and environmental benefits.
Wood construction could make a significant contribution to Chinas
green revolution.
50
Above: Wood frame house used for comparative energy study by Harbin
Institute of Technology
Wood frame construction (WFC) is considered by some to be
expensive. I have to explain this: In China at the present time
WFC is usually designed for villas with foreign housing
finish which is even more luxurious than our domestic high-
end finish. So the costs can get high. Changing the standard
of finishes, designing for low to middle-income people andlocalizing the production of materials, are certain to bring
costs down.
Mr. Zhu Guangqian, President, China Timber and Wood
Products Distribution Association, 2010
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Wood construction costs are becoming even more competitive in China
Wood construction costs in China are continuing to decline in
comparison with traditional construction. This is as a result of the
introduction and revision of building codes and standards, more
extensive training for design, construction and maintenance,
more building experience, new building methodologies and larger
scale construction.
Continuing cooperation between China and Europe and Canada in code
development, quality issues, cost-saving building techniques, training
and skill development, and research will accelerate improvements in
cost performance.
It is important that wood frame buildings are correctly and appropriately
designed and constructed to achieve their full efficiency and cost-saving
potential. On balance, any meaningful comparison of competitiveness
must move beyond costs alone into a broader evaluation of all the major
performance attributes, where wood construction outperforms
traditional construction in many other respects.
51
Above: Wood frame replacement housing Qingchuan county, Sichuan
Right: Light-weight wood frame storeys can be added to new or existing
multi-storey concrete buildings
While modern wood construction in China is very recent, there
is evidence that the overall cost of wood buildings, when
considered over the full life cycle, combined with superior
performance relating to energy and the environment, seismic
safety, and comfort, will provide better value for the developer
and the homeowner in comparison with traditional
construction systems.
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5
Safety anddurabilityCodes and standards ensure wood buildings
are constructed for safety and durability
Wood frame construction has superiorseismic performance, even in the mostsevere earthquakes
Fire safety is assured by fire-rated, finishedassemblies, which have been fire-testedin China
Different climatic conditions requireappropriate detailing
Surveys in China demonstrate the durabilityof wood buildings
Design and construction practices arebacked by extensive research
53
Seismic safety
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Wood frame construction has superior seismic performance
Wood frame buildings are safer than concrete and masonry buildings in
areas with a high risk of earthquakes. They save lives and reduce the
cost of reconstruction.
Wood is strong, light and flexible. Wood buildings weigh less than
concrete buildings. This reduces loads on the structure, as well as the
danger of heavy weights falling from above. The flexibility of the wood
components allows the structure to deform and deflect momentarily in
response to seismic forces without breakage, collapse or disconnection.
Uplift and lateral loads are shared by the many wood members that
make up the framework, the wood structural panels fastened to them,
and the thousands of fasteners and connectors which tie the
components together. This structural redundancy is stronger than
predicted by conventional engineering analysis.
Additional measures can be taken in areas of greatest risk
In areas such as Sichuan, where severe earthquakes are likely, the
structural design of a standard wood frame can be enhanced simply and
inexpensively. Additional measures include braced walls, reinforced
connections between foundation and floor, and walls to roof, as well as
steel rod tie-downs that clamp the top wall to the foundation.
Engineered shear wall
Tongji University is actively involved in research to determine howwell wood construction performs under seismic conditions. We
tested a full scale, two storey wood building on our shake table,
simulating the most severe of earthquakes. The wood building
performed well and without problems.
Professor He Minjuan, Executive Dean of the College of
Continuing Education, Tongji University, March 2010
Above: Site of Beichuan middle school tragedy, Sichuan
Wood structural
panels of specific
grade and thickness
Specific stud species
Base shear
anchor bolts
Specific nail size and
spacing requirements
Hold down
anchors
f f
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A survey of wood frame construction in severe
earthquakes world-wide23
The survey covers wood frame buildings of all ages and provides
evidence of the superior safety of wood frame buildings in severe
earthquakes world-wide, including Japan and the United States.
A very high proportion of wood platform frame buildings survived
peak ground accelerations of 0.6 g and greater with no collapse or
serious structural damage. The resulting injuries and deaths were
few. There were very few specific failures, as for example from hillside
collapses. Virtually all modern wood frame buildings survived with
no visible damage.
Right: Three undamaged modern wood frame buildings (background) next toan older building ( foreground) whose ground floor has collapsed completely,Nishinomiya, Japan. Hyogo-ken Nanbu Earthquake, 1995.
Earthquake Richter Estimated number Total number Casualties in
Magnitude of wood platform frame of casualties wood platform
M houses strongly shaken frame houses
Alaska,
USA, 1964 8.4 - 130
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A survey of wood frame construction following the Wenchuan
earthquake, Sichuan24
A survey was conducted following the tragic earthquake of May 12, 2008.
The evidence showed that wood frame buildings had outperformedbuildings constructed from other materials. They suffered only minor
damage, while many brick infill walls collapsed and concrete buildings
suffered severe damage.
In Dujiangyan, 40 km NW of Chengdu, about 21 km from the epicentre of
the Wenchuan earthquake, many concrete and masonry structures were
seriously damaged. Many collapsed, including three school buildings.
Although not all the concrete and masonry collapsed, masonry infillwalls were severely damaged, causing potential danger to occupants.
Reconstruction is now underway in the Sichuan area. Chinese
authorities and specialists are working closely with Canadian and
European counterparts in the support of the rebuilding, which includes
houses, schools, and special facilities. These are permanent structures,
meeting all building code requirements.
This is a good example of how light wood frame construction is proving
to be cost-competitive in rural China, and responsive to local needs in
regions where annual incomes are low. Moreover, these newly
constructed wood-framed buildings are comfortable, energy-efficient,
with lower annual energy costs, and resistant to severe earthquakes.
56
Left: Wood-frame houses survived the Wenchuan earthquake with only minor damage,which could be easily repaired
Above: Beichuan, 100 km northwest of Chengdu, after the Wenchuan earthquake
The capability of a building to absorb seismic energy is a key
point, in addition to the performance of its structural system.
The damping of a steel structure is usually low. The damping of
a concrete and brick hybrid structure is high, but the dampingof WFC is even higher WFC has performed well in many
earthquakes and reduced casualties. There were a lot of
traditional buildings that collapsed in the Wenchuan earthquake
in May 2008, but wood frame buildings suffered no damage.
Prof. Lu Xilin, Dean of the Institute of Structural Engineering
and Disaster Reduction, Civil Engineering College,
Tongji University, March 2010
S i ti t th l t t h th b i f b ildi d
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Scientists use the latest research as the basis for building codes
International scientists have been working closely with Chinese experts
on seismic testing of wood frame building, using the shake test table
facility at Tongji University. They aim to provide technical data on seismic
performance. This will be used to develop building codes further, as
well as to establish seismic safety design guidelines for wood frame
construction and wood hybrid structures. The seismic intensities used
for testing were comparable to the extreme earthquakes of California. 25
Tests show multi-storey hybrid structures can survive the
most severe earthquakes
A full-scale, seven-storey mixed use condominium tower (six wood
frame storeys above a one-storey steel structure) was tested. Conducted
in Kobe, Japan, this was the largest full-scale earthquake test in the
world. The building was subjected to a simulated quake that was 180
per cent of the Northridge earthquake in California, and suffered no
significant damage. This demonstrates that even mid-rise wood
buildings can survive the most severe earthquakes. The test used
Japans massive E-Defense Shake Table, the largest shake table in
the world.
Above: Shake table test, Tongji University, Shanghai
Left: Seismic test of 6-storey wood frame building, Japan
Fire safety
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Buildings constructed from wood have to meet the same fire safety
codes as all other buildings
All countries take fire safety very seriously. In China, wood buildings
must meet the same fire codes and standards and safety performance
levels which apply to other forms of construction. In fact, when new
systems, such as wood frame, or glulam construction are first
introduced into a country like China, fire safety codes tend to be
overly cautious because of the lack of domestic experience with the
building system.
Building regulations in Europe and North America have been based on
function, rather than material, for many years. They stipulate what fire
load the structural assemblies and members must be able to withstand
and then require the designer to demonstrate that the stipulations can
be met.
Extensive research into the fire performance of structural wood
assemblies and materials used in wood frame construction is now well
underway in China. The Tianjin Fire Research Institute is working closely
with fire safety research specialists from Europe, Canada, and theUnited States. They are assessing fire safety relating to new
opportunities for wood construction in China and ensuring fire safety
codes are up to date with the latest research (see Chapter 7, Codes
and standards).
International fire safety statistics show no difference in losses between
countries which use wood extensively in construction and those which
do not. In North America and Europe, statistics show that people are
just as safe in a code-compliant wood frame house as they are in a
code-compliant house built of light frame steel, concrete, or masonry.
The limits for fire safety performance of large structural wood members
can be readily determined and incorporated into building design. As
wood burns in a predictable and controlled manner, it is possible to
estimate how much of the cross-section of a structural member will
remain unaffected by fire after a specified period of burning. Dimensions
can then be specified to ensure the unaffected part of the cross section
has the ability to bear the required load over the specified period.
Steel, on the other hand, loses all its load-bearing capacity at the
temperatures of a fully developed fire.
Top left: Tianjin Fire Research Institute (TFRI) fire test of structural glulam
column (in fire test furnace), 2007
Top right: TFRI fire test of wood frame wall assembly; thermo-couples attached togypsum plaster board cladding; (below) after the test, 2007
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The controlled charring rate of wood is clearly demonstrated when fire
testing for structural glue laminated timber. The charring rate is
0.7mm/min, and the remaining unaffected wood and its load bearing
capacity can be easily calculated as a function of time exposed to fire.
Fire safety depends on building assembly performance
In fact, fire safety performance in conventional wood frame construction
has little to do with the combustibility of the structural materials. It
relates to the finished building assemblies, like walls and roofs, whichare actually assessed in the tests. Wood framed assemblies are finished
on the interior with gypsum wall board panels. These have very low
combustibility ratings. Cavities are filled with non-combustible, mineral
fibre insulation. Testing requires these assemblies to be burned under
controlled conditions in fire research laboratories at very high
temperatures until they fail structurally. Wood framed structural wall
and roof assemblies are required to survive these high temperatures for
a minimum of one hour before structural failure.
Moreover, fire safety in low and medium density housing of all types
is rarely related to structural failure, but rather to the inhalation of
toxic smoke and gas. Fewer than 0.25 per cent of fire fatalities in these
buildings are caused by the collapse of roofs, walls, or floors. Non-
flammable surface materials, sprinkler systems and smoke detectorscan be used to ensure safety from toxic gases during the early stages
of a fire. Codes require that all buildings, including wood, be designed
and constructed to provide residents with a fast and easy exit in the
event of fire.
Top: Structural glulam beam after fire test. Wood surface chars at a predictablerate. The remaining uncharred wood retains its structural strength
Above: Wood burns at a predictable rate
Right: Gypsum wall board lining fulfilling fire requirements
We have been working closely with European and Canadian
research scientists and fire safety specialists to study the fire
resistance performance and safety aspects of wood buildings in
China. Extensive fire tests of wooden frame assemblies and
structural glulam have been carried out at TFRI national fire lab.
This research will assist us in determining appropriate, fire-safe
applications of wood products in construction assemblies, as well
as the codes that relate to these uses. We expect that this will lead
to new opportunities for wood in construction in China.
Mr. Ni Zhaopeng, Director, Tianjin Fire Research Institute;
Vice-Chairman of GB 50016 fire code committee, March 2010
Char layer
Pyrolysis zone
Normal wood
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Exterior wood products used for
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decks and other landscaping
projects are either made from
naturally durable wood species,such as the heartwood of China
fir, Western red cedar and yellow
cedar, or pressure treated with
chemical preservatives. Strict
environmental and health
regulations ensure these
chemicals are benign to humans
but resistant to insects and fungi.
Good design, workmanship, andmaintenance are also critical for
prolonging the service life of
outdoor wood products.
Modern wood frame construction has a good record of durability
Modern systems of wood frame construction also have a good record of
durability. This building type has a long history in Europe and North
America, and there are still houses standing from the original
developments. Many North American and European wood houses are
over a hundred years old. In 2005, 17 per cent of the US housing stock
was over 75 years old.
Wood frame is the most popular type of residential construction in North
America, even for areas like Hawaii and the Southern USA, where decay
and insect hazard are severe. Similar construction methods have also
been adopted in areas such as New Zealand, the UK, Japan, Korea and
China. Progress in design, material use and treatment, construction
techniques and maintenance have been made in recent decades to make
sure that wood buildings can endure indefinitely.
A survey on wood building service lives27
Buildings are rarely demolished because they are beyond repair, or have
become structurally unsound. Generally it is to make way for a larger or
more modern building. Simple to maintain and repair, wood buildings
are easily renovated to adapt to new requirements. At the end of their
economic service life, they can be demolished, with recovered materials
being reused, recycled or used as biomass energy.
Durability survey in China28
Forintek carried out a durability survey of wood frame houses in China
during 2006 and 2007. Results demonstrated that, with the durability
measures introduced into the relevant codes and standards in China,
including the Shanghai Technical Specification for Wood-Frame
Construction, wood construction in China is durable (See Chapter 7,Codes and standards).
0 10% 20% 30% 40% 50% 60%
Per cent of buildings
Above left: Liuhe Temple, Hangzhou, over 1,000 years old
Above right: 150 year old house, Canada - modern wood frame
construction has a good record of durability
0-25
26-50
51-75
76-100
100+
Distribution of 94 non-residential buildings by age class andstructural material
Ageclass
- years
ConcreteSteelWood
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Sustainable
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