Wood is the only major building material that grows naturally and is renewable. With growing pressure to reduce the carbon footprint of the built environment, building designers are increasingly being called upon to balance function and cost objectives of a building with reduced environmental impact. Wood can help to achieve that balance. Numerous life cycle assessment studies worldwide have shown that wood products yield clear environmental advantages over other building materials at every stage. Wood buildings can offer lower greenhouse gas emissions, less air pollution, lower volumes of solid waste and less ecological resource use.

Of all the energy used in North America, it is estimated that 30 to 40 percent is consumed by buildings. In Canada, the majority of operational energy in residential buildings is provided by natural gas, fuel oil, or electricity, and is consumed for space heating. Given the fact that buildings are a significant source of energy consumption and greenhouse gas emissions in Canada, energy efficiency in the buildings sector is essential to address climate change mitigation targets.

As outlined in the Pan-Canadian Framework on Clean Growth and Climate Change, the federal, provincial and territorial governments are committed to investment in initiatives to support energy efficient homes and buildings as well as energy benchmarking and labelling programs.

Despite the expanding number of choices for consumers, the most cost-effective way to increase building energy performance has remained unchanged over the decades:

• maximize the thermal performance of the building envelope by adding more insulation and reducing thermal bridging; and

• increase the airtightness of the building envelope.

The building envelope is commonly defined as the collection of components that separate conditioned space from unconditioned space (exterior air or ground). The thermal performance and airtightness of the building envelope (also known as the building enclosure) effects the whole-building energy efficiency and significantly affects the amount of heat losses and gains. Building and energy codes and standards within Canada have undergone or are currently undergoing revisions, and the minimum thermal performance requirements for wood-frame building enclosure assemblies are now more stringent. The most energy efficient buildings are made with materials that resist heat flow and are constructed with accuracy to make the best use of insulation and air barriers.

To maximize energy efficiency, exterior wall and roof assemblies must be designed using framing materials that resist heat flow, and must include continuous air barriers, insulation materials, and weather barriers to prevent air leakage through the building envelope.

The resistance to heat flow of building envelope assemblies depends on the characteristics of the materials used. Insulated assemblies are not usually homogeneous throughout the building envelope. In light-frame walls or roofs, the framing members occur at regular intervals, and, at these locations, there is a different rate of heat transfer than in the spaces between the framing members. The framing members reduce the thermal resistance of the overall wall or ceiling assembly. The rate of heat transfer at the location of framing elements depends on the thermal or insulating properties of the structural framing material. The higher rate of heat transfer at the location of framing members is called thermal bridging. The framing members of a wall or roof can account for 20 percent or more of the surface area of an exterior wall or roof and since the thermal performance of the overall assembly depends on the combined effect of the framing and insulation, the thermal properties of the framing materials can have a significant effect on the overall (effective) thermal resistance of the assembly.

Wood is a natural thermal insulator due to the millions of tiny air pockets within its cellular structure. Since thermal conductivity increases with relative density, wood is a better insulator than dense construction materials. With respect to thermal performance, wood-frame building enclosures are inherently more efficient than other common construction materials, largely because of reduced thermal bridging through the wood structural elements, including the wood studs, columns, beams, and floors. Wood loses less heat through conduction than other building materials and wood-frame construction techniques support a wide range of insulation options, including stud cavity insulation and exterior rigid insulation.

Research and monitoring of buildings is increasingly demonstrating the importance of reducing thermal bridging in new construction and reducing thermal bridges in existing buildings. The impact of thermal bridges can be a significant contributor to whole building energy use, the risk of condensation on cold surfaces, and occupant comfort.

Focusing on the building envelope and ventilation at the time of construction makes sense, as it is difficult to make changes to these systems in the future. High performance buildings typically cost more to build than conventional construction, but the higher purchase price is offset, at least in part, by lower energy consumption costs over the life cycle. What’s more, high performance buildings are often of higher quality and more comfortable to live and work in. Making buildings more energy efficient has also been shown to be one of the lowest cost opportunities to contribute to energy reduction and climate change mitigation goals.

Several certification and labeling programs are available to builders and consumers address reductions in energy consumption within buildings.

Natural Resources Canada (NRCan) administers the R-2000 program, which aims to reduce home energy requirements by 50 percent compared to a code-built home. Another program administered by NRCan, ENERGY STAR®, aims to be 20 to 25 percent more energy efficient than code. The EnerGuide Rating System estimates the energy performance of a house and can be used for both existing homes and in the planning phase for new construction.

Other certification programs and labelling systems have fixed performance targets. Passive House is a rigorous standard for energy efficiency in buildings to reduce the energy use and enhance overall performance. The space heating load must be less than 15 kWh/m² and the airtightness must be less than 0.6 air changes per hour at 50 Pa, resulting in ultra-low energy buildings that require up to 90 percent less heating and cooling energy than conventional buildings.

The NetZero Energy Building Certification, a program operated by the International Living Future Institute, is a performance-based program and requires that the building have net-zero energy consumption for twelve consecutive months.

Green Globes and Leadership in Energy and Environmental Design (LEED) are additional building rating systems that are prevalent in the building design and construction marketplace.

For further information, refer to the following resources:

Thermal Performance of Light-Frame Assemblies – IBS No.5 (Canadian Wood Council)

National Energy Code of Canada for Buildings

Natural Resources Canada

BC Housing

Passive House Canada

Green Globes

Canadian Green Building Council

North American Insulation Manufacturers Association (NAIMA)

International Living Future Institute

Concerns about climate change are encouraging decarbonization of the building sector, including the use of construction materials responsible for fewer greenhouse gas (GHG) emissions and improvements in operational performance over the life cycle of buildings. Accounting for over 10 percent of total GHG emissions in Canada, the building sector plays an important role in climate change mitigation and adaptation. Decreasing the climate change impacts of buildings offers high environmental returns for relatively low economic investment.

The Government of Canada, as a signatory to the Paris Agreement, has committed to reducing Canada’s GHG emissions by 30 percent below 2005 levels by 2030. In addition, the Pan-Canadian Framework on Clean Growth and Climate Change acknowledges that forest and wood products have the ability to contribute to the national emissions reductions strategy through:

• enhancing carbon storage in forests;
• increasing the use of wood for construction;
• generating fuel from bioenergy and bioproducts; and
• advancing innovation in bio-based product development and forest management practices.

The importance of the forestry and wood products sector as a critical component toward mitigating the effects of climate change is also echoed by the Intergovernmental Panel on Climate Change (IPCC); stating that a sustainable forest management strategy aimed at maintaining or increasing forest carbon stocks while producing timber, fibre, or energy, generates the largest sustained benefit to mitigate climate change. In addition, the IPCC proclaims that “mitigating options by the forest sector include extending carbon retention in HWP [harvested wood products], product substitution, and producing biomass for bioenergy.”

The Canadian forest industry is pledging to remove 30 megatons of carbon dioxide (CO₂) a year by 2030, equivalent to 13 percent of Canada’s national commitments under the Paris Agreement. Several mechanisms will be employed to meet this challenge, including:

• product displacement, using bio-based products in place of fossil fuel-derived products and energy sources;
• forest management practices, including increased utilization, improved residue use and land use planning, and better growth and yields;
• accounting for long-lived bio-based product carbon pools; and
• higher efficiencies in wood product manufacturing processes

Canada is home to 9 percent of the world’s forests, which have the ability to act as enormous carbon sinks by absorbing and storing carbon. Annually, Canada harvests less than one-half of one percent of its forest land, allowing for the forest cover in Canada to remain constant for last century. Sustainable forest management and legal requirements for reforestation continue to maintain this vast carbon reservoir. A forest is a natural system that is considered carbon neutral as long as it is managed sustainably, which means it must be reforested after harvest and not converted to other land uses. Canada has some of the strictest forest management regulations in the world, requiring successful regeneration after public forests are harvested. When managed with stewardship, forests are a renewable resource that will be available for future generations.

Canada is also a world leader in voluntary third-party forest certification, adding further assurance of sustainable forest management. Sustainable forest management programs and certification schemes strive to preserve the quantity and quality of forests for future generations, respect the biological diversity of the forests and the ecology of the species living within it, and respect the communities affected by the forests. Canadian companies have achieved third-party certification on over 150 million hectares (370 million acres) of forests, the largest area of certified forests in the world.

The forest represents one carbon pool, storing biogenic carbon in soils and trees. The carbon remains stored until the trees die and decay or burn. When a tree is cut, 40 to 60 percent of the biogenic carbon remains in the forest; the rest is removed as logs and much of it is transferred to the wood products carbon pool within the built environment. Wood products continue to store this biogenic carbon, often for decades in the case of wood buildings, delaying or preventing the release of CO₂ emissions.

Wood products and building systems have ability to store large amounts of carbon; 1 m³ of S-P-F lumber stores approximately 1 tonne of CO₂ equivalent. The amount of carbon stored within a wood product is directly proportional the density of the wood. The average single-family home in Canada stores almost 30 tonnes of CO₂ equivalent within the wood products used for its construction. Most bio-based construction products actually store more carbon in the wood fibre than is released during the harvesting, manufacturing and transportation stages of their life cycle.

In general, bio-based products like wood that are naturally grown with help from the sun have lower embodied emissions. The embodied emissions arise through the production processes of building materials, starting with resource extraction or harvesting through manufacturing, transportation, construction, and end-of-life. Bioenergy produced from bio-based residuals, such as tree bark and sawdust, is primarily used to generate energy for the manufacture of wood products in North America. Wood construction products have low embodied GHG emissions because they are grown using renewable solar energy, use little fossil fuel energy during manufacturing, and have many end-of-life options (reuse, recycle, energy recovery).

Wood products have the ability to substitute for other more carbon-intensive building materials and energy sources. GHG emissions are thereby avoided by using wood products instead of other more GHG-intensive building products. Displacement factors (kg CO₂ avoided per kg wood used) have been estimated to calculate the amount of carbon avoided through the use of wood products in building construction.

For further information, refer to the following resources:

Addressing Climate Change in the Building Sector – Carbon Emissions Reductions (Canadian Wood Council)

Resilient and Adaptive Design Using Wood (Canadian Wood Council)

CWC Carbon Calculator

Canada’s Forest Products Industry “30 by 30” Climate Change Challenge (Forest Products Association of Canada)

www.naturallywood.com

www.thinkwood.com

Building with wood = Proactive climate protection (Binational Softwood Lumber Council and State University of New York)

Natural Resources Canada

Pan-Canadian Framework on Clean Growth and Climate Change (Government of Canada)

Intergovernmental Panel on Climate Change

Construction products and the building sector as a whole have significant impacts on the environment. Policy instruments and market forces are increasingly pushing governments and businesses to document and report environmental impacts and track improvements. One tool that is available to help understand the environmental aspects related to new construction, renovation, and retrofits of buildings and civil engineering works is life cycle assessment (LCA). LCA is a decision-making tool that can help to identify design and construction approaches that yield improved environmental performance.

Several European jurisdictions, including Germany, Zurich and Brussels, have made LCA a mandatory requirement prior to issuing a building permit. In addition, the application of LCA to building design and materials selection is a component of green building rating systems. LCA can benefit manufacturers, architects, builders, and government agencies by providing quantitative information about potential environmental impacts and providing data to identify areas for improvement.

LCA is a performance-based approach to assessing the environmental aspects related to building design and construction. LCA can be used to understand the potential environmental impacts of a product or structure at every stage of its life; from resource extraction or raw material acquisition, transportation, processing and manufacturing, construction, operation, maintenance and renovation to the end-of-life.

LCA is an internationally accepted, science-based methodology which has existed in alternative forms since the 1960s. The requirements and guidance for conducting LCA has been established through international consensus standards; ISO 14040 and ISO 14044. LCA considers all input and output flows (materials, energy, resources) associated with a given product system and is an iterative procedure that includes goal and scope definition, inventory analysis, impact assessment, and interpretation.

The inventory analysis, also known as the life cycle inventory (LCI), consists of data collection and the tracking of all input and output flows within a product system. Publicly available LCI databases, such as the U.S. Life Cycle Inventory Database, are accessible free of charge in order to source this LCI data. During the impact assessment phase of the LCA, the LCI flows are translated into potential environmental impact categories using theoretical and empirical environmental modelling techniques. LCA is able to quantify potential environmental impacts and aspects of a product, such as:

• Global warming potential;
• Acidification potential;
• Eutrophication potential;
• Ozone depletion potential;
• Smog potential;
• Primary energy consumption;
• Material resources consumption; and
• Hazardous and non-hazardous waste generation.

LCA tools are available to building designers that are publicly accessible and user friendly. These tools allow designers to rapidly obtain potential environmental impact information for an extensive range of generic building assemblies or develop full building life cycle assessments on their own. LCA software offers building professionals powerful tools for calculating the potential life cycle impacts of building products or assemblies and performing environmental comparisons.

It is also possible to use LCA to perform objective comparisons between alternate materials, assemblies and whole buildings, measured over the respective life cycles and based on quantifiable environmental indicators. LCA enables comparison of the environmental trade-offs associated with choosing one material or design solution over another and, as a result, provides an effective basis for comparing relative environmental implications of alternative building design scenarios.

An LCA that examines alternative design options must ensure functional equivalence. Each design scenario considered, including the whole building, must meet building code requirements and offer a minimum level of technical performance or functional equivalence. For something as complex as a building, this means tracking and tallying the environmental inputs and outputs for the multitude of assemblies, subassemblies and components in each design option. The longevity of a building system also impacts the environmental performance. Wood buildings can remain in service for long periods of time if they are designed, built and maintained properly.

Numerous LCA studies worldwide have demonstrated that wood building products and systems can yield environmental advantages over other building materials and methods of construction. FPInnovations conducted a LCA of a four-storey building in Quebec constructed using cross-laminated timber (CLT). The study assessed how the CLT design would compare with a functionally equivalent concrete and steel building of the same floor area, and found improved environmental performance in two of six impact categories, and equivalent performance in the rest. In addition, at the end-of-life, bio-based products have the ability to become part of a subsequent product system when reused, recycled or recovered for energy; potentially reducing environmental impacts and contributing to the circular economy.

Life cycle of wood construction products

Photo source: CEI-Bois

For further information, refer to the following resources:

www.naturallywood.com

Athena Sustainable Materials Institute

Building for Environmental and Economic Sustainability (BEES)

FPInnovations. A Comparative Life Cycle Assessment of Two Multistory Residential Buildings: Cross-Laminated Timber vs. Concrete Slab and Column with Light Gauge Steel Walls, 2013.

American Wood Council

U.S. Life Cycle Inventory Database

ISO 14040 Environmental management – Life cycle assessment – Principles and framework

ISO 14044 Environmental management – Life cycle assessment – Requirements and guidelines