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

Life Cycle Assessment

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

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.

Durability by nature

For outdoor applications of wood, we have a strong tradition here in North America of using our naturally durable species: Western red cedar, Eastern white cedar, yellow cypress and redwood. These are familiar choices for decks, fences, siding and roofing. These species are resistant to decay in their natural state, due to high levels of organic chemicals called extractives. Extractives are chemicals that are deposited in the heartwood of certain tree species as they convert sapwood to heartwood. In addition to providing the wood with decay resistance, extractives also often give the heartwood colour and odour. Only the heartwood has these protective deposits. The sapwood of all North American softwoods is susceptible to decay and must be protected by other means when decay resistance is required. Sapwood is the newer part of the tree, closer to the bark. It needs no decay protection in the live tree because wound responses keep out any invading organisms. The heartwood is the inner, older part of the tree and is no longer alive. Heartwood is often visibly distinguishable from sapwood by colour (heartwood is generally darker), but not in all species. However, even if you’re sure you have heartwood of a durable species, you may not have the level of resistance you think. Decay resistance is often highly variable, and may be lower in plantation-grown trees. There is currently no way to reliably estimate the durability of a piece of naturally durable heartwood. More Information Click Here for a table showing natural durability rankings of common softwood species.

Durability by treatment

Treating Methods There are two basic methods of treating: with and without pressure. Non-pressure methods are the application of preservative by brushing, spraying or dipping the piece to be treated. These are superficial treatments that do not result in deep penetration or large absorption of preservative. Their use is best restricted to field treatment during construction (for example, when a pressure-treated piece of lumber must be field cut), to cases where only part of a piece is to be treated, to manufacturing processes for strand-based wood products, to surface protection against moulds or to remedial treatment of wood in place. For example, mixtures of borate and glycols are used to treat sound wood left in place during repair of decay problems. The glycol helps the borate to penetrate dry wood, arresting the activity of any fungus which contacts it. The penetration of the preservative is still limited, and the most important function is to prevent undetected fungus left in place from spreading to sound wood. Deeper, more thorough penetration is achieved by driving the preservative into the wood cells with pressure. Various combinations of pressure and vacuum are used to force adequate levels of chemical into the wood. Pressure-treating preservatives consist of chemicals carried in a solvent. The solvent, or carrier, is either water or oil. Oilborne preservatives are largely used for treating industrial products such as railway ties, utility poles and bridge timbers, and for protection of field cuts. Waterborne preservatives are more widely used in residential markets due to the absence of odour, the cleaner wood surface and the ability to paint or stain the wood product. When a wood product will be used in an application known to present a risk, for example outdoors, pressure-treatment is recommended. Types of Preservatives The mostly commonly used wood preservatives in North America for residential construction are waterborne copper-based systems, including alkaline copper quaternary (ACQ), copper azole (CA) and micronized copper azole (MCA). Wood treated with these preservatives has a natural green hue, though this may be masked by the use of colourants that most often give the treated wood a mid-brown colour. Copper is the primary biocide in these systems. ACQ also contains quaternary ammonium compounds that act as a co-biocide to protect against copper-tolerant organisms. Similarly, CA and MCA contain tebuconazole to protect against these organisms.  Chromated copper arsenate (CCA) was heavily used in residential construction until 2004 when its use in most residential applications was phased out. It is now largely limited to industrial applications, but can still be used in a few residential applications such as shakes and shingles and permanent wood foundations. Ammoniacal copper zinc arsenate (ACZA) can also be used in most of these applications, but is primarily favoured for treating Douglas-fir and for marine applications. Borates are another class of waterborne preservative used in North America. Their use is currently limited to applications which are protected from rain and other persistent sources of water. These include framing in termite areas and repair of decayed framing in leaky buildings where the main moisture source has been eliminated. Borates are also used as part of a dual treatment in conjunction with a creosote or copper naphthenate shell to protect railway ties. Metal-free waterborne preservative systems such as PTI and EL2 contain carbon-based fungicides and insecticides. Wood treated with these systems is used in residential construction in the United States, and is restricted to above-ground applications. Oilborne preservatives include creosote, pentachlorphenol, and copper- and zinc-naphthenate. Creosote is the well-known black oily wood preservative, the oldest type of preservative still in modern use. It’s now used in Canada almost exclusively for railroad ties, where its resistance to moisture movement is a key advantage. Pentachlorophenol in oil is mainly used for utility poles where the surface softening characteristics of the oil are useful in pole climbing. Copper naphthenate and zinc naphthenate are two common preservatives used for treating field cuts. Copper naphthenate is also used to treat ties and timbers in the United States. Thermal Modification The properties of wood are altered when it is exposed to high temperatures (160-260°C) under reduced oxygen conditions. Thermal modification kilns use much higher temperatures than drying kilns, and use steam (or other oxygen-excluding media) to protect the wood from degradation at these high temperatures. The resulting thermally modified wood generally has a darker colour, increased dimensional stability, and increased decay resistance. Thermal modification may reduce some mechanical properties and does not protect wood against insects. Thermally modified wood is typically used in non-structural, above-ground applications, such as siding, decking and outdoor furniture. More information from Producers of Wood Preservative Products Lonza Wood Protection Timber Specialties  Viance LLC  Genics Inc.  Kop-Coat   Rio Tinto Minerals Nisus   Creosote council   KMG Chemicals   Wood Preservation Canada  

Finishing Exterior Wood

The appearance of wood can be modified with the application of an architectural coating. Architectural coatings are surface coverings such as paints and stains applied to a building or exterior structures such as a deck. Coatings are multi-functional: decorative, reduce the effort needed to clean buildings and structures, and provide protection against moisture uptake and helping extend the life of wood. However, coatings cannot be considered as substitutes for preservative treatment. On this page, we explain the basics of different types of exterior wood coatings, and what they can and can’t do for wood. Types of Coatings – Opacity Architectural coatings available for wood generally include paints, stains, varnishes and water repellents. There are a number of ways to classify coatings. One common method is to differentiate based on appearance. Coatings are often identified as: 1) Opaque; 2) semi-transparent or 3) transparent.  These terms indicate how much of the natural wood features will be visible through the finish.  An opaque coating doesn’t allow any of the wood’s natural colour to show through and depending on thickness may also hide much or all of its surface texture. It effectively protects the wood from damage caused by sunlight. It can also help keep moisture out of the wood.  These coatings tend to last the longest. Opaque coatings include paints and solid colour stains. A transparent or semi-transparent finish such as a stain or water repellent may change the colour of the wood, but because it allows the grain and texture to show through, the wood still looks “natural.”  These finishes help keep moisture out of the wood to some extent but there is considerable variation between stains in their ability to restrict moisture ingress. They also help protect the wood from sunlight damage to varying degrees depending on their content of organic UV absorbers or inorganic pigments. The difference between transparent and semi-transparent coatings is also sometimes unclear.  Transparent coatings allow more grain and texture to show through. Transparent exterior coatings labeled as “clear” may still contain some pigment to enhance wood’s natural colour and provide a visual distinction between painted and unpainted areas during application. However, it is important to note that clear products intended for interior use only are NOT appropriate for exterior use, as they will quickly degrade and fail if exposed to sunlight and weather. There are many transparent products marketed as providing water protection for wood (water repellents) – these might technically be considered wood “treatments” rather than wood coatings as they mainly provide water protection and help reduce checking (splitting), and provide very limited, if any, UV protection.  This means they usually fail earlier than pigmented finishes, but they do help slow down the weathering process by restricting water ingress.  Note that water repellents are often solvent-borne and contain wax which affects the adhesion of subsequent coatings, which means most of these products should not be used as a pre-treatment beneath paint.  However, transparent water repellents have the unique benefit of being the most aesthetically-forgiving treatment when there is lack of maintenance.  In other words, these products don’t change the colour of the wood, so bare patches of wood are not as visible if the coating wears away. Types of Coatings – Carriers Another common way of categorizing coatings is by the type of carrier (the base) – products are either water-borne or solvent-borne.  When low volatile organic compounds (VOCs) and easy clean-up are important, a water-borne product is the better choice.  Water-borne coatings now dominate the market due to increasing environmental regulatory requirements around air quality and health, and customer demand.  Compared to solvent-borne finishes, water-borne finishes usually have less odour and can be cleaned up with water instead of requiring mineral spirits. Water-borne coatings are generally more flexible (less prone to cracking as the wood beneath shrinks and swells from moisture changes) and more vapour permeable.  Water-borne paints are often called latex. Solvent-borne paints are commonly known as oil paints.  Also, paints labeled as alkyds are typically solvent-borne (but not always).  Although it is popular to refer to paints as either latex or oil/alkyd, it is more useful to think of them as water-borne versus solvent-borne. Water-borne coatings, particularly acrylics, are generally less prone to fading and chalking than alkyds. The technology for water-borne paints and finishes has advanced significantly in recent years and is now mature to the extent they can match or exceed the properties of solvent-borne products. Types of Coatings – Film Thickness Sometimes wood coatings are classified by the thickness of film they form on the surface of the wood.  Paints, solid colour stains, and varnishes are often called film-formers, as these create a layer of continuous material sitting on top of the wood.  Semi-transparent stains, transparent stains, water repellents and natural oils are often referred to as penetrating finishes, since they penetrate through the pores of the wood, leaving its surface texture and pores visible, rather than leaving a thick film on top of the wood. However, all coatings leave a film on the surface – thick for some, thin for others – and the “penetrating” products only penetrate a very short distance into the wood.  Nonetheless, it’s helpful to know if a product leaves a thick film, as this type of product can be more difficult to remove if degraded and requiring refinishing.  This is because their failure modes are different – a thick coherent coating like paint fails by cracking and peeling, whereas a thin-film “penetrating” product such as a stain fails by erosion. Can Coatings Protect Wood? Coatings can temporarily protect the surface of wood from sunlight, moisture and weathering, but coatings do not actively protect against decay.  Their purpose is primarily aesthetic. But they slow down the damaging effects of weathering, and do provide some moisture protection, which is a decay factor.  Coatings also help preserve the natural durability of species like western red cedar, by helping to prevent the natural protective agents in this wood from washing out.  The protective benefits of all coatings are, of course, dependent on proper maintenance of the coating.  No coating will last indefinitely, and all need to be periodically reapplied. Weathering

Non-Pressure Treated Wood

Non-Pressure Treated Wood For most treated wood, preservatives are applied in special facilities using pressure. However, sometimes this isn’t possible, or the need for treated wood was not apparent until after construction or building occupancy. In those cases, preservatives can be applied using methods that do not involve pressure vessels. Some of these treatments can only be done by licensed applicators. When using wood preservatives, as with all pesticides, the label requirements of the Pest Management Regulatory Agency (in Canada) or the EPA (in the USA) must be followed. Five categories of non-pressure treatments Treatment during Engineered Wood Product Manufacture Some engineered wood panel products, such as plywood and laminated veneer lumber (LVL) are able to be treated after manufacture with preservative solutions, whereas thin strand based products (OSB, OSL) and small particulate and fibre-based panels (particleboard, MDF) are not. The preservatives must be added to the wood elements before they are bonded together, either as a spray on, mist or powder. Products such as OSB are manufactured from small, thin strands of wood. Powdered preservatives can be mixed in with the strands and resins during the blending process just prior to mat forming and pressing. Zinc borate is commonly used in this application. By adding preservatives to the manufacturing process it’s possible to obtain uniform treatment throughout the thickness of the product.  In North America, plywood is normally protected against decay and termites by pressure treatment processes. However, in other parts of the world insecticides are often formulated with adhesives to protect plywood against termites. Surface pre-treatment This is anticipatory preservative treatment applied by dip, spray or brush application to all of the accessible surfaces of some wood products during the construction process. The intent is to provide a shell of protection to vulnerable wood products, components or systems in their finished form. One example would be spraying house framing with borates for resistance to drywood termites and wood boring beetles in some cases. Such treatments may also be applied to lumber, plywood and OSB to provide additional protection against mould growth. Sub-surface pre-treatment (Depot treatment) This is preservative treatment applied at discrete locations, not to the entire piece, during the manufacturing process or during construction. The intent is to pro-actively provide protection only to the parts of the wood product, component or systems that might be exposed to conditions conducive to decay. One example would be placing borate rods into holes drilled in the exposed ends of glulam beams projecting beyond a roof line. Supplementary treatment This is preservative treatment applied at discrete locations to treated wood in service to compensate for either incomplete initial penetration of the cross section, or depletion of preservative effectiveness over time. The intent is to boost the protection in previously-treated wood, or to address areas exposed by necessary on-site cutting of treated wood products. One example would be the application of a ready-made bandage to utility poles that have suffered depletion of the original preservative loading. Another example is field-cut material for preserved wood foundations. Remedial treatment This is preservative treatment applied to residual sound wood in products, components or systems where decay or insect attack is known to have begun. The intent is to kill existing fungi or insects and/or prevent decay or insects from spreading beyond the existing damage. One example would be roller or spray application of a borate/glycol formulation on sound wood left in place adjacent to decayed framing (which should be cut out and replaced with pressure-treated wood). Formats of non-pressure treatments Non-pressure treatments come in three different forms: solids, liquids/pastes, and fumigants. Unlike pressure-treatment preservatives, which rely on pressure for good penetration, these rely on the mobility of the active ingredients to penetrate deep enough in wood to be effective. The active ingredients can move in the wood via capillarity or can diffuse in water and/or air within the wood. This mobility not only allows the active ingredients to move into the wood but can also allow them to move out under certain conditions. This means the conditions within and around the structure must be understood so the loss of preservative and consequent loss of protection can be minimized. Borates, fluorides and copper compounds are particularly suitable for use as solids, liquids and pastes. Methyl isothiocyanate (and its precursors), methyl bromide, and sulfuryl fluoride are the only widely used fumigant treatments. Methyl bromide was phased out, except for very limited uses, in 2005. Solids The major advantage of solids in these applications is that they maximize the amount of water-soluble material that can be placed into a drilled hole, due to the high percentage of active ingredients contained in commercially-available rods. The major disadvantage is the requirement for sufficient moisture and the time needed for the rod to dissolve. The earliest and best-known solid preservative system is the fused borate rod, originally developed in the 1970s for supplementary and remedial treatment of railroad ties. These have since been used successfully on utility poles, timbers, millwork (window joinery), and a variety of other wood products. A mixture of borates is fused into glass at extremely high temperatures, poured into a mould and allowed to set. Placed into holes in the wood, the borate dissolves in any water contained in the wood and diffuses throughout the moist region. Mass flow of moisture along the grain may speed up distribution of the borate. Secondary biocides such as copper can be added to borate rods to supplement the efficacy of the borates against decay and insects. While all preservatives should be treated with respect, many users feel more comfortable dealing with borate and copper/borate rods because of their low toxicity and low potential for entry into the body. Fluorides are also currently available in a rod form. The rod is produced by compressing sodium fluoride and binders together, or by encapsulation in a water-permeable tubing. Fluorides diffuse more rapidly than borates in water and may also move in the vapour phase as hydrofluoric acid. Zinc borate (ZB) is a powder