Combustible construction
The provision of fire safety in a building is a complex matter; far more complex than the relative combustibility of the main structural materials used in a building. To develop safe code provisions, prevention, suppression, movement of occupants, mobility of occupants, building use, and fuel control are but a few of the factors that must be considered in addition to the combustibility of the structural components. Fire-loss experience shows that building contents play a large role in terms of fuel load and smoke generation potential in a fire. The passive fire protection provided by the fire-resistance ratings on the floor and wall assemblies in a building assures structural stability in a fire. However, the fire-resistance rating of the structural assemblies does not necessarily control the movement of smoke and heat, which can have a large impact on the level of safety and property damage resulting from fire. The National Building Code of Canada (NBC) categorizes wood buildings as ‘combustible construction’. Despite being termed combustible, common construction techniques can give wood frame construction fire-resistance ratings up to two hours. When designed and built to code requirements, wood buildings provide the same level of life safety and property protection required for comparably sized buildings defined under the NBC as ‘noncombustible construction’. Wood has been used for virtually all types of buildings, including; schools, warehouses, fire stations, apartment buildings, and research facilities. The NBC sets out guidelines for the use of wood in applications that extend well beyond the traditional residential and small building sector. The NBC allows wood construction of up to six storeys in height, and wood cladding for buildings designated to be of noncombustible construction. When meeting the area and height limits for the various NBC building categories, wood frame construction can meet the life safety requirements by making use of wood-frame assemblies (usually protected by gypsum wallboard) that are tested for fire-resistance ratings. The allowable height and area restrictions can be extended by using fire walls to break a large building area into smaller separate building areas. The recognized positive contribution to both life safety and property protection which comes from the use of automatic sprinkler systems can also be used to increase the permissible area of wood buildings. Sprinklers typically operate very early in a fire thereby quickly controlling the damaging effects. For this reason, the provision of automatic sprinkler protection within a building greatly improves the life safety and property protection prospects of all buildings including those constructed of noncombustible materials. The NBC permits the use of ‘heavy timber construction’ in buildings where combustible construction is required to have a 45-minute fire-resistance rating. This form of heavy timber construction is also permitted to be used in large noncombustible buildings in certain occupancies. To be acceptable, the components must comply with minimum dimension and installation requirements. Heavy timber construction is afforded this recognition because of its performance record under actual fire exposure and its acceptance as a fire-safe method of construction. In sprinklered buildings permitted to be of combustible construction, no fire-resistance rating is required for the roof assembly or its supports when constructed from heavy timber. In these cases, a heavy timber roof assembly and its supports would not have to conform to the minimum member dimensions stipulated in the NBC. Mass timber elements may also be used whenever combustible construction is permitted. In those instances, however, such mass timber elements need to be specifically designed to meet any required fire-resistance ratings. NBC definitions: Combustible means that a material fails to meet the acceptance criteria of CAN/ULC-S114, “Test for Determination of Non-Combustibility in Building Materials.” Combustible construction means that type of construction that does not meet the requirements for noncombustible construction. Heavy timber construction means that type of combustible construction in which a degree of fire safety is attained by placing limitations on the sizes of wood structural members and on thickness and composition of wood floors and roofs and by the avoidance of concealed spaces under floors and roofs. Noncombustible construction means that type of construction in which a degree of fire safety is attained by the use of noncombustible materials for structural members and other building assemblies. Noncombustible means that a material meets the acceptance criteria of CAN/ULC-S114, “Test for Determination of Non-Combustibility in Building Materials.” For further information, refer to the following resources: National Building Code of Canada CAN/ULC-S114 Test for Determination of Non-Combustibility in Building Materials Wood Design Manual 2017
Encapsulated mass timber construction
In addition to combustible, heavy timber and noncombustible construction, a new construction type is presently being considered for inclusion into the National Building Code of Canada (NBC). Encapsulated mass timber construction (EMTC) is proposed to be defined as the “type of construction in which a degree of fire safety is attained by the use of encapsulated mass timber elements with an encapsulation rating and minimum dimensions for the structural timber members and other building assemblies.” EMTC is neither ‘combustible construction’ nor ‘heavy timber construction’ nor ‘noncombustible construction’, as defined within the NBC. EMTC is required to have an encapsulation rating. The encapsulation rating is the time, in minutes, that a material or assembly of materials will delay the ignition and combustion of encapsulated mass timber elements when it is exposed to fire under specified conditions of test and performance criteria, or as otherwise prescribed by the NBC. The encapsulation rating for EMTC is determined through the ULC S146 test method. In order for structural wood elements to be considered ‘mass timber’, they must meet minimum size requirements, which are different for horizontal (walls, floors, roofs, beams) and vertical (columns, arches) load-bearing elements and dependent on the number of sides that the element is exposed to fire. EMTC construction in Canada is expected to be limited to a height of twelve-storeys, that is, the uppermost floor level may be a maximum of 42 m (137 ft) above the first floor. An EMTC building must be sprinklered throughout according to NFPA 13 and it is likely that some mass timber will also be able to be exposed in the suites. All EMTC elements are expected to have a minimum two-hour fire resistance rating and the building floor area to be limited to 6,000 m2 for Group C occupancy and 7,200 m2 for Group D occupancy. There are restrictions on the use of exterior cladding elements in EMTC, as well as other restrictions on the use of; combustible roofing materials, combustible window sashes and frames, combustible components in exterior walls, nailing elements, combustible flooring elements, combustible stairs, combustible interior finishes, combustible elements in partitions, and concealed spaces. If any encapsulation material is damaged or removed, it will be required to be repaired or replaced so that the encapsulation rating of the materials is maintained. Additionally, requirements related to construction site fire safety are to be applied to construction access, standpipe installation and protective encapsulation. EMTC and its related provisions are anticipated to be included in the NBC 2020. NBC definitions: Combustible means that a material fails to meet the acceptance criteria of CAN/ULC-S114, “Test for Determination of Non-Combustibility in Building Materials.” Combustible construction means that type of construction that does not meet the requirements for noncombustible construction. Heavy timber construction means that type of combustible construction in which a degree of fire safety is attained by placing limitations on the sizes of wood structural members and on thickness and composition of wood floors and roofs and by the avoidance of concealed spaces under floors and roofs. Noncombustible construction means that type of construction in which a degree of fire safety is attained by the use of noncombustible materials for structural members and other building assemblies. Noncombustible means that a material meets the acceptance criteria of CAN/ULC-S114, “Test for Determination of Non-Combustibility in Building Materials.” For further information, refer to the following resources: Guide to Encapsulated Mass Timber Construction in the Ontario Building Code ULC S146 Standard Method of Test for the Evaluation of Encapsulation Materials and Assemblies of Materials for the Protection of Mass Timber Structural Members and Assemblies Fire performance of mass-timber encapsulation methods and the effect of encapsulation on char rate of cross-laminated timber (Hasburgh et al., 2016) CAN/ULC-S114 Test for Determination of Non-Combustibility in Building Materials NFPA 13 Standard for the Installation of Sprinkler Systems
Tall Wood Buildings
With advanced construction technologies and modern mass timber products such as glued-laminated timber, cross-laminated timber and structural composite lumber, building tall with wood is not only achievable but already underway – with completed contemporary buildings in Australia, Austria, Switzerland, Germany, Norway and the United Kingdom at 9 storeys and taller. Increasingly recognized by the construction sector as an important, new, and safe construction choice, the reduced carbon footprint and embodied / operational energy performance of these buildings is appealing to communities that are committed to sustainable development and climate change mitigation. Tall wood buildings, built with renewable wood products from sustainably managed forests, have the potential to revolutionize a construction industry increasingly focused on being part of the solution when it comes to urban intensification and environmental impact reduction. The Canadian wood product industry is committed to building on its natural advantage, through the development and demonstration of continuously improving wood-based building products and building systems. A tall wood building is a building over six-storeys in height (top floor is higher than 18 m above grade) that utilizes mass timber elements as a functional component of its structural support system. With advanced construction technologies and modern mass timber products such as glued-laminated timber (glulam), cross-laminated timber (CLT) and structural composite lumber (SCL), building tall with wood is not only achievable but already underway – with completed contemporary buildings in Canada, US, Australia, Austria, Switzerland, Germany, Norway, Sweden, Italy and the United Kingdom at seven-storeys and taller. Tall wood buildings incorporate modern fire suppression and protection systems, along with new technologies for acoustic and thermal performance. Tall wood buildings are commonly employed for residential, commercial and institutional occupancies. Mass timber offers advantages such as improved dimensional stability and better fire performance during construction and occupancy. These new products are also prefabricated and offer tremendous opportunities to improve the speed of erection and quality of construction. Some significant advantages of tall wood buildings include: the ability to build higher in areas of poor soils, as the super structure and foundations are lighter compared to other building materials; quieter to build on site, which means neighbours are less likely to complain and workers are not exposed to high levels of noise; worker safety during construction can be improved with the ability to work off large mass timber floor plates; prefabricated components manufactured to tight tolerances can reduce the duration of construction; tight tolerances in the building structure and building envelope coupled with energy modelling can produce buildings with high operational energy performance, increased air tightness, better indoor air quality and improved human comfort Design criteria for tall wood buildings that should be considered include: an integrated design, approvals and construction strategy, differential shrinkage between dissimilar materials, acoustic performance, behaviour under wind and seismic loads, fire performance (e.g., encapsulating the mass timber elements using gypsum), durability, and construction sequencing to reduce the exposure of wood to the elements. It is important to ensure early involvement by a mass timber supplier that can provide design assistance services that can further reduce manufacturing costs through the optimization of the entire building system and not just individual elements. Even small contributions, in connection designs for example, can make a difference to the speed of erection and overall cost. In addition, mechanical and electrical trades should be invited in a design-assist role at the outset of the project. This allows for a more complete virtual model, additional prefabrication opportunities and quicker installation. Recent case studies of modern tall wood buildings in Canada and around the world showcase the fact that wood is a viable solution for attaining a safe, cost-effective and high-performance tall building. For more information, refer to the following case studies and references: Brock Commons Tall Wood House (Canadian Wood Council) Origine Point-aux-Lievres Ecocondos,Quebec City (Cecobois) Wood Innovation and Design Centre (Canadian Wood Council) Technical Guide for the Design and Construction of Tall Wood Buildings in Canada (FPInnovations) Ontario’s Tall Wood Building Reference (Ministry of Natural Resources and Forestry & Ministry of Municipal Affairs) Summary Report: Survey of International Tall Wood Buildings (Forestry Innovation Investment & Binational Softwood Lumber Council) www.thinkwood.com/building-better/taller-buildings
Mid-Rise Buildings
When it comes to wood construction, many people think of basic 2×4 framing, panels or flooring for single-family homes. However, advances in wood science and building technology have resulted in stronger, more sophisticated and robust products that are expanding the options for wood construction, and providing more choices for builders and architects. The Canadian Wood Council’s support for mid-rise construction is not unique In Ontario, Home Builders, through organizations such as RESCON, BILD and the Ontario Home Builders Association are also highlighting this opportunity. Mid-rise buildings made of wood are a new construction option for builders. That’s good news for main-street Canada, where land is so expensive. The net benefit of reduced construction costs is increased affordability for home buyers. In terms of new economic opportunity, the ability to move forward “now” creates new construction jobs in cities and supports employment in forestry communities. This also offers increased export opportunities for current and innovative wood products, where adoption in Canada provides the example for other countries. This also reflects a new standard of engineering in that structural, fire and seismic concerns have all been addressed by the expert committees of the Canadian Commission on Building and Fire Codes. In the end, when occupied, mid-rise buildings fully meet the same requirements of the Building Code as any other type of construction from the perspective of health, safety and accessibility.
Bridges
Timber bridges have a long history as vital components of the roadway, railway and logging road networks within Canada. Dependent on the availability of materials, technology, and labour, the design and construction of wood bridges has evolved significantly over the last 200 hundred years throughout North America. Wood bridges take on many forms and use alternative support systems; including simple span log bridges, different types of trussed bridges, and stress-laminated or composite bridge decks and components. Timber bridges remain an important part of our transportation network in Canada. The benefits of building modern timber bridges include: The different types of materials used to construct wood bridges include: sawn lumber, round logs, straight and curved glued-laminated timber (glulam), laminated veneer lumber (LVL), parallel strand lumber (PSL), cross-laminated timber (CLT), nail-laminated timber (NLT), and composite systems such as stress-laminated decks, wood-concrete laminated decks, and fibre-reinforced polymers. Two main wood species used for wood bridge construction in Canada are Douglas fir and the Spruce-Pine-Fir species combination. Other species within the Hem-Fir and Northern species combinations are also recognized under CSA O86, however, they are less commonly used in bridge construction. All metal fasteners used for bridges must be protected against corrosion. The most common method for providing protection is hot dip galvanizing, a process whereby a sacrificial metal is added to exterior of the fastener. Different fastener types that are used in wood bridge construction include, but are not limited to, bolts, lag screws, split rings, shear plates, and nails (for deck laminations only). All highway bridges in Canada must be designed to meet the requirements outlined in CSA S6 and CSA O86. The CSA S6 standard requires that the main structural components of any bridge in Canada, regardless of construction type, be able to withstand a minimum of 75 years of loading during its service life. The style and span of bridges varies greatly depending on the application. In hard to reach locations with deep valleys, timber trestle bridges were common at the end of the 19th century and into the beginning of the 20th century. Historically, trestle bridges relied heavily on ample timber resources and in some cases, were considered to be temporary. Initial construction of North America’s transcontinental railways would not have been possible without the use of timbers to construct bridges and trestles. Many examples of trussed timber bridges for have been built for well over a century. Trussed bridges allow for longer spans compared to simple girder bridges and historically had spans in the range of 30 to 60 m (100 to 200 ft). Bridges that are designed with trusses located above the deck provide a great opportunity to build a roof over the roadway. Installing a roof overhead is an excellent way to shed water away from the main bridge structure and protect it from the sun. The presence of these covered roofs is the main reason these century-old covered bridges remain in service today. The fact that they remain part of our landscape is as much a testament to their hardiness as to their attractiveness. Although originally devised as a rehabilitation measure for aging bridge decks, the stress-laminating technique has been extended to new bridges through the application of stressing at the time of original construction. Stress-laminated decks provide improved structural behaviour, through their excellent resistance to the effects of repeated loading. Three main considerations related to durability of wood bridges include protection by design, preservative treatment of wood, and replaceable elements. A bridge can be designed such that it is inherently self-protecting by deflecting water away from the structural elements. Preservative treated wood has the ability to resist the effects of de-icing chemicals and attack by biotic agents. Lastly, the bridge should be designed such that, at some point in its future, a single element can be replaced relatively easily, without significant disruption or cost. For further information, refer to the following resources: Wood Highway Bridges (Canadian Wood Council)Ontario Wood Bridge Reference Guide (Canadian Wood Council)CSA S6 Canadian Highway Bridge Design CodeCSA O86 Engineering design in wood
Tall Wood Buildings – Research
Tests Current research includes the World’s largest mass timber fire test – click here for updates on the test results currently being conducted https://firetests.cwc.ca/ Studies “The Historical Development of the Building Size Limits in the National Building Code of Canada (17 Mb) “Case Studies of Risk-to-Life due to Fire in Mid- and High-Rise, Combustible and Non-combustible Buildings Using CUrisk“, by Xia Zhang and George Hadjisophocleous of Carleton University, and Jim Mehaffey of CHM Fire Consultants Ltd. (March 2015) (2.3 Mb) “Fire Safety Challenges of Tall Wood Buildings”, by Robert Gerard and David Barber – Arup North America Ltd; Armin Wolski, San Francisco, CA; for the National Fire Protection Association’s Fire Protection Research Foundation (December 2013) “The Case for Tall Wood Buildings – How Mass Timber Offers a Safe, Economical, and Environmentally Friendly Alternative for Tall Building Structures“, by mgb ARCHITECTURE + DESIGN, Equilibrium Consulting, LMDG Ltd, and BTY Group (February 2012) (8.5 Mb) Ontario Tall Wood Reference Guide (8.04 MB) Reports Fire Research Final Report – Full-scale Mass Timber Shaft Demonstration Fire (including the National Research Council test report as an Appendix), by FPInnovations (April 2015) Acoustics Research and Guides RR-331: Guide to calculating airborne sound transmission in buildings (2nd Edition), by the National Research Council (April 2016) Tall Wood Building Demonstration Initiative Test Reports (funding provided by Natural Resources Canada) CLT Diaphragm Properties CLT Firestopping Testing Monotonic Quasi-Static Testing of CLT Connections Shear Modulus of CLT in plan loading Shear Testing of Cross-Laminated Beams Full Scale Exterior Wall Test on Nordic CLT System, by the National Research Council (January 2015) Client Report A1-005991.1 – Fire Endurance of Cross-Laminated Timber Floor and Wall Assemblies for Tall Wood Buildings, by the National Research Council (December 2014) Measurement of Airborne Sound Insulation of Wall & Floor Assemblies Visit Think Wood’s Research Library for additional resources
Mid-Rise Buildings – Research
Studies General “The Historical Development of the Building Size Limits in the National Building Code of Canada“, by Sereca for CWC (2015) (17 Mb) Structural & Seismic Vertical Movement in Wood Platform Frame Structures (CWC Fact Sheets) Basics Design and detailing solutions Movement prediction Design of multi-storey wood-based shearwalls: Linear dynamic analysis & mechanics based approach A Mechanics-based Approach for Determining Deflections of Stacked Multi-storey Wood-based Shearwalls Design of Stacked Multi-storey Wood Shearwalls using a Mechanics Based Approach Linear Dynamic Analysis for Wood Based Shear Walls and Podium Structures Design of wood frame and podium structures using linear dynamic analysis, by Newfield, G., Ni, C., and Wang, J., Proceedings of the World Conference on Timber Engineering 2014, Quebec City, Canada (2014) Testing Other Reports Final Report – Full-scale Mass Timber Shaft Demonstration Fire (including the National Research Council test report as an Appendix), by FPInnovations (April 2015) Full Scale Exterior Wall Test on Nordic CLT System, by the National Research Council (January 2015) Report No. 101700231SAT-003_Rev.1 – Report of Testing Cross-Laminated Timber Panels for Compliance with CAN/ULC-S101 Standard Methods of Fire Endurance Tests of Building Construction and Materials: Loadbearing 3-ply CLT Wall with 1 Layer of 5/8″ Type X Gypsum Board – 1 hr FRR, by Intertek for CWC (November 2014) Report No. 100585447SAT-002B – Report of Testing Cross-Laminated Timber Panels for Compliance with CAN/ULC-S101 Standard Methods of Fire Endurance Tests of Building Construction and Materials: Loadbearing 3-ply CLT Wall with 1 Layer of 5/8″ Fire-rated Gypsum Board (60% load) – 1 hr FRR, by Intertek for CWC (December 2013) Report No. 100585447SAT-002A_Rev.1 – Report of Testing Cross-Laminated Timber Panels for Compliance with CAN/ULC-S101 Standard Methods of Fire Endurance Tests of Building Construction and Materials: Loadbearing 3-ply CLT Wall with Attached Wood-frame Partition – 1 hr FRR, by Intertek for CWC (January 2012) Visit Think Wood’s Research Library for additional resources
Green
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.
Energy Efficiency
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
Climate Change
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
Permanent Wood Foundations
A permanent wood foundation (PWF) is an engineered construction system that uses load-bearing exterior light-frame wood walls in a below-grade application. A PWF consists of a stud wall and footing substructure, constructed of approved preservative-treated plywood and lumber, which supports an above-grade superstructure. Besides providing vertical and lateral structural support, the PWF system provides resistance to heat and moisture flow. The first PWF examples were built as early as 1950 and many are still being used today. A PWF is a strong, durable and proven engineered system that has a number of unique advantages: energy savings resulting from high insulation levels, achievable through the application of stud cavity insulation and exterior rigid insulation (up to 20% of heat transfer can occur through the foundation); dry, comfortable living space provided by a superior drainage system (which does not require weeping tile); increased living space since drywall can be attached directly to foundation wall studs; resistance to cracking from freeze/thaw cycles; adaptable to most building designs, including crawl spaces, additions and walk-out basements; one trade required for more efficient construction scheduling; buildable during winter with minimal protection around footings to protect them from freezing; rapid construction, whether framed on site or pre-fabricated off-site; materials are readily available and can be efficiently shipped to rural or remote building sites; and long life, based on field and engineering experience. PWFs are suitable for all types of light-frame construction covered under Part 9 ‘Housing and Small Buildings’ of the National Building Code of Canada (NBC), that is, PWF can be used for buildings up to three-storeys in height above the foundation and having a building area not exceeding 600 m2. PWFs can be used as foundation systems for single-family detached houses, townhouses, low-rise apartments, and institutional and commercial buildings. PWFs can also be designed for projects such as crawlspaces, room additions and knee-wall foundations for garages and manufactured homes. There are three different types of PWFs: concrete slab or wood sleeper floor basement, suspended wood floor basement and an unexcavated or partially excavated crawl space. Lumber studs used in PWF are typically 38 x 140 mm (2 x 6 in) or 38 x 184 mm (2 x 8 in), No. 2 grade or better. Improved moisture control methods around and beneath the PWF result in comfortable and dry below-grade living space. The PWF is placed on a granular drainage layer which extends 300 mm (12 in) beyond the footings. An exterior moisture barrier, applied to the outside of the walls, provides protection against moisture ingress. Caulked joints between all exterior plywood wall panels and at the bottom of exterior walls is intended to control air leakage through the PWF, but also eliminates water penetration pathways. The result is a dry basement that can be easily insulated and finished for maximum comfort and energy conservation. All lumber and plywood used in a PWF, except for specific components or conditions, must be treated using a water-borne wood preservative and identified as such by a certification mark stating conformance with CSA O322. Corrosion-resistant nails, framing anchors and straps that are used to fasten PWF-treated material must be hot-dipped galvanized or stainless steel. Exterior moisture and vapour barriers must be at least 0.15 mm (6 mil) in thickness. Dimpled drainage board is often specified as an exterior moisture barrier. For further information, refer to the following references: Permanent Wood Foundations (Canadian Wood Council) Permanent Wood Foundations 2023 – Durable, Comfortable, Adaptable, Energy efficient, Economical (Wood Preservation Canada and Canadian Wood Council) Wood Design Manual (Canadian Wood Council) Wood Preservation Canada CSA S406 Specification of permanent wood foundations for housing and small buildings CSA O322 Procedure for certification of pressure-treated wood materials for use in permanent wood foundations CSA O86 Engineering design in wood National Building Code of Canada
Durability by design
“Durability by design” is the most important aspect of durable solutions. It starts with using dry wood, storing it appropriately to ensure it stays dry, and then designing the building to protect the wood or, if the wood will be exposed, designing to not accumulate moisture. It includes ensuring the building envelope is appropriately designed to shed bulk water, mitigating water and vapour from getting into the envelope, and draining water that does leak into the envelope.
