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
Environmental Issues
Safe Handling Using common sense and standard safety equipment (personal protection and wood-working machinery) applies when working with any building products. Gloves, dust masks and goggles are appropriate for use with all woodworking. Here are a few key points specific to treated wood: Pressure-treated wood is not a pesticide, and it is not a hazardous product. In most municipalities, you may dispose of treated wood by ordinary garbage collection. However, you should check with your local regulations. Never burn treated wood because toxic chemicals may be produced as part of the smoke and ashes. If preservatives or sawdust accumulate on clothes, launder before reuse. Wash your work clothes separately from other household clothing. Treated wood used for patios, decks and walkways should be free of surface preservative residues. Treated wood should not be used for compost heaps where free organic acids produced early in the composting process can remove the fixed chemicals. It is, however, safe to use for growing vegetables in raised soil beds. If, after reading this, you are still concerned, place a layer of plastic sheet between the soil and the treated wood wall. Treated wood should not be cleaned with harsh reducing agents since these can also remove the fixed chemicals. Environmental Concerns All wood preservatives used in the U.S. and Canada are registered and regularly re-examined for safety by the U.S. Environmental Protection Agency and Health Canada’s Pest Management and Regulatory Agency, respectively. Wood preservation is not an exact science, due to the biological – and therefore variable and unpredictable – nature of both wood and the organisms that destroy it. Wood scientists are trying to understand more about how wood decays to ensure that durability is achieved through smart design and construction choices where possible, so that as a society we can be selective in our use of preservatives. Comparing treated wood to alternative products A series of life cycle assessments has been completed comparing preservative treated wood to alternative products. In most cases, the treated wood products had lower environmental impacts. Click for consumer safety information on handling treated wood (Canada). Read More
Environmental product declarations (EPDs)
Stakeholders within the building design and construction community are increasingly being asked to include information in their decision-making processes that take into consideration potential environmental impacts. These stakeholders and interested parties expect unbiased product information that is consistent with current best practices and based on objective scientific analysis. In the future, building product purchasing decisions will likely require the type of environmental information provided by environmental product declarations (EPDs). In addition, green building rating systems, including LEED®, Green Globes™ and BREEAM®, recognize the value of EPDs for the assessment of potential environmental impacts of building products. EPDs are concise, standardized, and third-party verified reports that describe the environmental performance of a product or a service. EPDs are able to identify and quantify the potential environmental impacts of a product or service throughout the various stages of its life cycle (resource extraction or harvest, processing, manufacturing, transportation, use, and end-of-life). EPDs, also known as Type III environmental product declarations, provide quantified environmental data using predetermined parameters that are based on internationally standardized approaches. EPDs for building products can help architects, designers, specifiers, and other purchasers better understand a product’s potential environmental impacts and sustainability attributes. An EPD is a disclosure by a company or industry to make public the environmental data related to one or more of its products. EPDs are intended to help purchasers better understand a product’s environmental attributes in order for specifiers to make more informed decisions selecting products. The function of EPDs are somewhat analogous to nutrition labels on food packaging; their purpose is to clearly communicate, to the user, environmental data about products in a standardized format. EPDs are information carriers that are intended to be a simple and user-friendly mechanism to disclose potential environmental impact information about a product within the marketplace. EPDs do not rank products or compare products to baselines or benchmarks. An EPD does not indicate whether or not certain environmental performance criteria have been met and does not address social and economic impacts of construction products. Data reported in an EPD is collected using life cycle assessment (LCA), an internationally standardized scientific methodology. LCAs involve compiling an inventory of relevant energy and material inputs and environmental releases, and evaluating their potential impacts. It is also possible for EPDs to convey additional environmental information about a product that is outside the scope of LCA. EPDs are primarily intended for business-to-business communication, although they can also be used for business-to-consumer communication. EPDs are developed based on the results of a life cycle assessment (LCA) study and must be compliant with the relevant product category rules (PCR), which are developed by a registered program operator. The PCR establishes the specific rules, requirements and guidelines for conducting an LCA and developing an EPD for one or more product categories. The North American wood products industry has developed several industry wide EPDs, applicable to all the wood product manufacturers located across North America. These industry wide EPDs have obtained third-party verification from the Underwriters Laboratories Environment (ULE), an independent certification body. North American wood product EPDs provide industry average data for the following environmental metrics: Global warming potential; Acidification potential; Eutrophication potential; Ozone depletion potential; Smog potential; Primary energy consumption; Material resources consumption; and Non-hazardous waste generation. Industry wide EPDs for wood products are business-to-business EPDs, covering a cradle-to-gate scope; from raw material harvest until the finished product is ready to leave the manufacturing facility. Due to the multitude of uses for wood products, the potential environmental impacts related to the delivery of the product to the customer, the use of the product, and the eventual end-of-life processes are excluded from the analysis. For further information, refer to the following resources: ISO 21930 Sustainability in buildings and civil engineering works – Core rules for environmental product declarations of construction products and services ISO 14025 Environmental labels and declarations – Type III environmental declarations – Principles and procedures ISO/TS 14027 Environmental labels and declarations – Development of product category rules ISO 14040 Environmental management – Life cycle assessment – Principles and framework ISO 14044 Environmental management – Life cycle assessment – Requirements and guidelines American Wood Council Canada Green Building Council Green Globes BREEAM® Annual Review Rules and Form EPD
EPDs
Environmental product declarations (EPDs) Stakeholders within the building design and construction community are increasingly being asked to include information in their decision-making processes that take into consideration potential environmental impacts. These stakeholders and interested parties expect unbiased product information that is consistent with current best practices and based on objective scientific analysis. In the future, building product purchasing decisions will likely require the type of environmental information provided by environmental product declarations (EPDs). In addition, green building rating systems, including LEED®, Green Globes™ and BREEAM®, recognize the value of EPDs for the assessment of potential environmental impacts of building products. EPDs are concise, standardized, and third-party verified reports that describe the environmental performance of a product or a service. EPDs are able to identify and quantify the potential environmental impacts of a product or service throughout the various stages of its life cycle (resource extraction or harvest, processing, manufacturing, transportation, use, and end-of-life). EPDs, also known as Type III environmental product declarations, provide quantified environmental data using predetermined parameters that are based on internationally standardized approaches. EPDs for building products can help architects, designers, specifiers, and other purchasers better understand a product’s potential environmental impacts and sustainability attributes. An EPD is a disclosure by a company or industry to make public the environmental data related to one or more of its products. EPDs are intended to help purchasers better understand a product’s environmental attributes in order for specifiers to make more informed decisions selecting products. The function of EPDs are somewhat analogous to nutrition labels on food packaging; their purpose is to clearly communicate, to the user, environmental data about products in a standardized format. EPDs are information carriers that are intended to be a simple and user-friendly mechanism to disclose potential environmental impact information about a product within the marketplace. EPDs do not rank products or compare products to baselines or benchmarks. An EPD does not indicate whether or not certain environmental performance criteria have been met and does not address social and economic impacts of construction products. Data reported in an EPD is collected using life cycle assessment (LCA), an internationally standardized scientific methodology. LCAs involve compiling an inventory of relevant energy and material inputs and environmental releases, and evaluating their potential impacts. It is also possible for EPDs to convey additional environmental information about a product that is outside the scope of LCA. EPDs are primarily intended for business-to-business communication, although they can also be used for business-to-consumer communication. EPDs are developed based on the results of a life cycle assessment (LCA) study and must be compliant with the relevant product category rules (PCR), which are developed by a registered program operator. The PCR establishes the specific rules, requirements and guidelines for conducting an LCA and developing an EPD for one or more product categories. The North American wood products industry has developed several industry wide EPDs, applicable to all the wood product manufacturers located across North America. These industry wide EPDs have obtained third-party verification from the Underwriters Laboratories Environment (ULE), an independent certification body. North American wood product EPDs provide industry average data for the following environmental metrics: Global warming potential; Acidification potential; Eutrophication potential; Ozone depletion potential; Smog potential; Primary energy consumption; Material resources consumption; and Non-hazardous waste generation. Industry wide EPDs for wood products are business-to-business EPDs, covering a cradle-to-gate scope; from raw material harvest until the finished product is ready to leave the manufacturing facility. Due to the multitude of uses for wood products, the potential environmental impacts related to the delivery of the product to the customer, the use of the product, and the eventual end-of-life processes are excluded from the analysis. For further information, refer to the following resources: ISO 21930 Sustainability in buildings and civil engineering works – Core rules for environmental product declarations of construction products and services ISO 14025 Environmental labels and declarations – Type III environmental declarations – Principles and procedures ISO/TS 14027 Environmental labels and declarations – Development of product category rules ISO 14040 Environmental management – Life cycle assessment – Principles and framework ISO 14044 Environmental management – Life cycle assessment – Requirements and guidelines American Wood Council Canada Green Building Council Green Globes BREEAM®
Factory Finishing
Select heartwood where possible to minimize nutrient content of wood surfaces and prevent nutrients migrating through the coating to support fungal growth on the surface. Round all corners to minimum 5 mm radius to eliminate sharp edges where coating can thin out. Prepare surface by sanding with 100 grit sandpaper to physically and chemically activate the surface. Pretreatment and coating should be applied immediately after sanding. Research shows sanding can double coating life. Pretreat with an aqueous formulation containing a UV absorber designed to absorb the visible light that must penetrate transparent coatings to permit the wood to be visible. If the subsequent coating is not completely opaque to UV light, a hindered amine light stabilizer should be added to the visible light protection system. Not only does a visible light protection system prevent degradation of the wood-coating interface, it also prevents release of lignin breakdown products that can be used as a food source by black-stain fungi and prevents light induced breakdown of the biocide components. This pre-treatment must also contain three low-dose carbon-based biocides with differing chemistries to provide cross protection against detoxification and with complementary spectra of activity providing resistance to the full range of black-stain fungi. It should ideally have water repellent properties and must maintain wood surface pH close to neutral or slightly alkaline. Apply a transparent water-based catalyzed urethane coating, containing organic and inorganic UV absorbers with absorbance that extends from UVB through to the high-energy part of the visible spectrum (violet light). The coating must virtually eliminate UV from penetrating to the wood, preventing breakdown of wood, biocides and water repellents. This coating will be formulated to be damp-wood friendly to allow application soon after pre-treatment. It will contain no nutrients for fungal growth. It must have an optimum combination of moisture excluding efficiency and vapour permeability to minimize moisture uptake and allow drying after rain. The first coat to be designed to penetrate and bond to the wood, subsequent coats to be designed to ensure maximum intercoat adhesion without sanding between coats. Sufficient coats to be applied to give a film thickness no less than 60 microns to minimize the ability of black-stain fungi to penetrate the film with their infection pegs. The surface layer to have sheeting rather than beading properties to ensure rapid drying after rain or dew, reducing the time available for spore germination. Additional detailed information on coating wood surfaces has been assembled by the Joint Coatings and Forest Products Committee (http://www.fpl.fs.fed.us/documnts/pdf2004/fpl_2004_bonura001.pdf, 2004).
FAQs
What do the experts have to say about wood-frame mid-rise construction? Graham Finch, Building Science Research Engineer Michael Green, Principal, Michael Green Architecture Mid-rise Wood Construction – a detailed look at a changing landscape (Part 1) Mid-rise Wood Construction – a detailed look at a changing landscape (Part 2) Seven-storey wood-frame earthquake test BC Housing is supporting wood-frame construction for seniors’ rental housing Is mid-rise and tall wood building construction a new phenomenon: Wood-frame and heavy timber construction (up to ten storeys) was the norm in the early 1900’s, and many of these buildings still exist and are in use in many Canadian cities. Check them out here: http://www.flickr.com/photos/bobkh/337920532/. Over the past 10 years, there is a revival in the use of wood for both mid-rise (up to six-storeys) and tall buildings. In British Columbia alone, as of December 2013, there were over 250 five- and six-storey wood product based mid-rise buildings either in the design or construction phase. Why have code change proposals? This 2015 building code change is not about favoring wood over other building materials; it’s about acknowledging, via the highly thorough code process, that science-based innovation in wood products and building systems can and will lead to more choices for builders and occupants. Are these buildings safe? Regardless of the building material in question, nothing gets built unless it meets code. Mid-rise wood-frame buildings reflect 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. As an example, when it comes to concerns from firefighters, there is increased sprinkler protection for concealed spaces and balconies, greater water supply for fire protection, restrictions on types of building claddings used and increased consideration for access by firefighters . In the end, when occupied, these buildings fully meet the same requirements of the Building Code as any other type of construction from the perspective of health, safety and accessibility. What are some of the new safety provisions being proposed? Fire safety: Increased level of sprinkler / water protection: More concealed spaces sprinklered Balconies must be sprinklered Greater water supply for fire protection Non-combustible or limited combustible exterior wall cladding on 5th and 6th storey 25% of perimeter must face one street (within 15m of street) for firefighter access Seismic and wind provisions: Similar to BC Building Code Guidance (Appendix) on impact of increased rain and wind loads for 5- and 6-storey Acoustics: Requirements for Apparent Sound Transmission Class (ASTC) Supported by science from FPInnovations, NRC and many others. Doesn’t wood burn? No building material is impervious to the effects of fire. The proposed code changes go above and beyond the minimum requirements outlined in the NBCC. Health, safety, accessibility, fire and structural protection of buildings remain the core objectives of the NBCC and wood industry at large. What about construction site safety? The Canadian Wood Council has developed construction site fire safety guides which outline best practices and safety precautions to take during the construction phase of a building. Are mid-rise wood-frame buildings cost effective? For the most part, yes. Mid-rise wood-frame buildings are often a less expensive construction option for builders. This is good news for main-street Canada where land is so expensive. The recommended changes to the National Building Code of Canada (NBCC) would give the opportunity to erect safe, code compliant buildings that would otherwise not be possible. 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.
Fasteners
Fasteners, Connectors and Flashing for Wood Treated With Copper-Based Preservatives The presence of moisture is a precondition for corrosion of metals. Treated wood is typically used in applications where it may be exposed to moisture for considerable periods so any fasteners and connectors used with treated wood must also be resistant to these conditions. In addition, most wood preservatives designed for exterior use contain copper that may react with the metals used to fabricate fasteners and connectors therefore, it is important to use the right type of fastener and/or connectors. Where treated wood is used in dry environments to prevent damage by wood-destroying insects, including termites, corrosion is of less concern. Users and specifiers should also be aware that corrosive industrial, or salt air, environments may also require the use of appropriate corrosion resistant metals. Types of Wood Preserving Treatments Most copper-based preservatives are corrosive to unprotected fasteners and connectors. More recent systems such as MCA where the copper isn’t introduced in an ionic salt form, are designed to reduce the corrosion of metals, and the preserved wood is approved for use in contact with aluminum (e.g. brackets or outdoor furniture legs). Borate treatments do not increase the risk of corrosion. Recommendations on Connectors for Treated Wood Connectors used for wood treated with a copper-based preservative must be manufactured from steel either hot–dipped galvanized in accordance with ASTM A653 or hot dipped galvanized after manufacture in accordance with ASTM A123. Galvanizing nails and screws is actually a sacrificial coating to protect the structural integrity of the fastener, and the presence of some white corrosion product on the surface is normal. Red rust appearing is an indicator of coating failure. The service life of these components can be extended by using a barrier membrane between the connector and the treated wood surface. Stainless steel connectors (type 304 or 316) should be used for maximum service life, for high preservative retentions (i.e. ground contact products) or severe applications such as salt spray environments. For borate-treated wood used inside buildings, the same connectors can be used as for untreated wood. Recommendations on Fasteners for Treated Wood Fasteners for use in treated wood that will be exposed to the weather should be selected to withstand weathering as long as the treated wood itself. As a minimum, nails for wood treated with a copper-based preservative must be hot-dipped galvanized in accordance with ASTM A153. Hot-dipped galvanized nails should not be fastened using a high pressure nail gun due to the risk of damage to the coating during firing. The protective coating on electroplated galvanized fasteners is too thin and will perform poorly, and common nails will corrode rapidly after fastening most copper-based treated wood. Stainless steel should be used for maximum service life, for high preservative retentions or severe applications such as salt spray environments. Where appropriate, copper fasteners may also be used. Fasteners used in combination with metal connectors must be the same type of metal to avoid galvanic corrosion caused by dissimilar metals. For example stainless steel fasteners should not be used in combination with galvanized connectors. Screws intended for use on wood treated with a copper-based preservative must be hot dipped galvanized in accordance with ASTM A153 or, if recommended by the manufacturer and the preservative supplier, high-quality polymer coated. Stainless steel should be used for maximum service life, for high preservative retentions or severe applications such as salt spray environments. For borate treated wood used inside buildings, the same fasteners can be used as for untreated wood. As a general rule aluminum fasteners should not be used with treated wood, except new generation products (MCA treated) specifically tested, approved and labelled as suitable for contact with Aluminum. Recommendations on Flashing for Treated Wood Flashing used in contact with treated wood must be compatible with the treated wood and be last long enough to be suitable for the intended application. Flashing must also be of the same type of metal as any fasteners that penetrate through them to avoid galvanic corrosion. Copper and stainless steel are the most durable metals for flashing. Galvanized steel, in accordance with ASTM A653, G185 designation, is also suitable for use as flashing. Other Fasteners, Connectors or Hardware as Recommended by the Manufacturer There may be additional products such as polymer or ceramic coatings for fasteners, or vinyl or plastic flashings that are suitable for use with treated wood products. Consult the individual fastener, connector or flashing manufacturer for recommendations for use of their products with treated wood. Current Recommendations for Drying and Conditioning of Treated Wood Prior to Construction. Wood treated with copper-based preservatives should be at the least surface dried at the treating plant, in the store or at the job site before attachment of fasteners, connectors, flashing or other hardware. A moisture meter with a calibration for preservative treated wood should be used to verify that the wood is within a similar moisture content range to untreated construction lumber (i.e. about 12 to 18%) otherwise the treated wood can undergo similar shrinkage related cracking and deformation as incorrectly conditioned untreated lumber. Canadian Preservation Industry Canada has had a wood preservation industry for more than 100 years. Canada is tied with the UK as the world’s second largest producer of treated wood (the USA is first, by a large margin). In 1999, the most recent year for which we have data, Canada produced 3.5 million cubic metres of treated wood. There are about 60 treating plants in Canada. As with most other industrialized countries, Canada developed a wood preservation industry using creosote, initially to service railroads (the ties holding the rails) and then utilities (power poles). Creosote production began declining by the 1950s, and by the 1970s was being somewhat replaced for these traditional uses by pentachlorophenol. Today, these oil-borne preservatives only constitute 17% of Canadian treated wood production. The remaining 83% of production uses water-borne preservatives such as CCA, ACQ, CA and MCA. The industry began its substantial shift to the water borne
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
Finishing Quick Tips
For new wood, remember: The wood must be dry. Drying time depends on a few factors. Ideally the wood should be kiln-dried (stamped “S-DRY”, “KD” or “KDAT”, see glossary of “dry lumber”). If the wood is surface wet from rain or washing, let dry 1 to 2 days. If the wood is wet through (green lumber, pressure-treated lumber not stamped “KDAT”), 2 days of drying is acceptable if using a “damp-friendly” coating. Otherwise: The wood must be allowed to thoroughly dry to a stable outdoor moisture content; about 15% in most climates. The characteristics of the wood and the climatic characteristics of its environment are so variable that drying time is hard to predict. The common way to determine wood moisture content is with a moisture meter. (Note: specific correction factors should be applied if a moisture meter is used on preservative-treated wood.) Weather conditions during coating application can affect the coating’s drying, appearance and performance. Follow the coating manufacturer’s recommendation. Coat as soon as possible after the wood has been planed or sanded. Apply finishes within two weeks of exposure, or sooner if possible (Surface Preparation for Fresh Wood). Otherwise, follow the instructions for aged (weathered) wood below. If the wood is very smooth, lightly sand it to roughen the surface with 100-120 grit sand paper. This greatly improves the coating bond. Brush free of dirt and sawdust. If painting the wood, apply a primer coat. Use an extractive-blocking primer, if needed (for example, with western red cedar or redwood) over the entire piece, or a knot sealing primer if needed (Special Considerations). When dry, apply two coats of top quality paint. For stains and water repellents, follow the instructions on the can regarding number of coats. Carefully follow the instructions on the can regarding best environmental conditions for coating, application recommendations, safety precautions and clean-up. For aged (weathered) wood, remember: For wood that has been previously coated, please read about refinishing. Clean the wood and remove discolourations such as iron stain, if desired. Expose fresh wood because coatings perform best when applied to freshly exposed wood surfaces. Allow to dry. See Surface Preparation for Aged Wood. Brush free of dirt and sawdust, and proceed with application of the coating. When maintaining or refinishing, remember: Avoid the need to refinish by keeping an eye on the coating and adding a fresh coat before the previous coat wears away, cracks or peels. This may be as frequent as every six months with water repellents, every year or two with stains, and every few years with paint (See Maintenance). Spot-treat worn areas to extend the period between full applications of a fresh coat. Sand away any failed coating and any weathered wood, and re-apply the coating (See Maintenance). If the coating has failed on a large scale, or the coating is getting too thick for refinishing, or if a change in type of coating is desired, completely strip away the old coating – please read about refinishing.
Fire Code
National Fire Code of Canada The National Building Code of Canada (NBC) and the National Fire Code of Canada (NFC), both published by the National Research Council of Canada (NRC) and developed by the Canadian Commission on Building and Fire Codes (CCBFC), are developed as companion documents. The NBC establishes minimum standards for the health and safety of the occupants of new buildings. It also applies to the alteration of existing buildings, including changes in occupancy. The NBC is not retroactive. That is, a building constructed in conformance with a particular edition of the NBC, which is in effect at the time of its construction, is not automatically required to conform to the subsequent edition of the NBC. That building would only be required to conform to an updated version of the NBC if it were to undergo a change in occupancy or alterations which invoke the application of the new NBC in effect at the time of the change in occupancy or major alteration. The NFC addresses fire safety during the operation of facilities and buildings. The requirements in the NFC, on the other hand, are intended to ensure the level of safety initially provided by the NBC is maintained. With this objective, the NFC regulates: the conduct of activities causing fire hazards the maintenance of fire safety equipment and egress facilities limitations on building content, including the storage and handling of hazardous products the establishment of fire safety plans The NFC is intended to be retroactive with respect to fire alarm, standpipe and sprinkler systems. In 1990, the NFC was revised to clarify that such systems “shall be provided in all buildings where required by and in conformance with the requirements of the National Building Code of Canada.” This ensures that buildings are adequately protected against the inherent risk at the same level as the NBC would require for a new building. It does not concern other fire protection features such as smoke control measures or firefighter’s elevators. The NFC also ensures that changes in building use do not increase the risk beyond the limits of the original fire protection systems. The NBC and the NFC are written to minimize the possibility of conflict in their respective contents. Both must be considered when constructing, renovating or maintaining buildings. They are complementary, in that the NFC takes over from the NBC once the building is in operation. In addition, older structures which do not conform to the most current level of fire safety can be made safer through the requirements of the NFC. The most recent significant changes in the NFC relate the construction of six-storey buildings using combustible construction. As a result, eight additional protection measures related to mid-rise combustible buildings have been added to address fire hazards during construction when fire protection features are not yet in place. For further information, refer to the following resources: Fire Safety Design in Buildings (Canadian Wood Council) Codes Canada – National Research Council of Canada National Building Code of Canada National Fire Code of Canada Fire Safety and Security: A Technical Note on Fire Safety and Security on Construction Sites in Ontario/British Columbia (Canadian Wood Council)
Fire Fighting in Canada Article – Timber Tower
Article by Len Garis and Karin Mark.
When assistant deputy fire chief Ray Bryant heard about construction of the tallest wood building in the world in Vancouver, his reaction was predictable. “I thought it was an insane idea,” Bryant said. But once Bryant learned about the compartment-style construction of the student residence at the University of British Columbia, his opinion changed. “I couldn’t believe how safe it is,” he said. Read the article.
Fire Resistance
In the National Building Code of Canada (NBC) “fire-resistance rating” is defined in part as: “the time in minutes or hours that a material or assembly of materials will withstand the passage of flame and the transmission of heat when exposed to fire under specified conditions of test and performance criteria…” The fire-resistance rating is the time, in minutes or hours, that a material or assembly of materials will withstand the passage of flame and the transmission of heat when exposed to fire under specified conditions of test and performance criteria, or as determined by extension or interpretation of information derived therefrom as prescribed in the NBC. The test and acceptance criteria referred to in the NBC are contained in a standard fire test method, CAN/ULC-S101, published by ULC Standards. Horizontal assemblies such as floors, ceilings and roofs are tested for fire exposure from the underside only. This is because a fire in the compartment below presents the most severe threat. For this reason, the fire-resistance rating is required from the underside of the assembly only. The fire-resistance rating of the tested assembly will indicate, as part of design limitations, the restraint conditions of the test. When selecting a fire-resistance rating, it is important to ensure that the restraint conditions of the test are the same as the construction in the field. Wood-frame assemblies are normally tested with no end restraint to correspond with normal construction practice. Partitions or interior walls required to have a fire-resistance rating must be rated equally from each side, since a fire could develop on either side of the fire separation. They are normally designed symmetrically. If they are not symmetrical, the fire-resistance rating of the assembly is determined based on testing from the weakest side. For a loadbearing wall, the test requires the maximum load permitted by design standards be superimposed on the assembly. Most wood-stud wall assemblies are tested and listed as loadbearing. This allows them to be used in both loadbearing and non-loadbearing applications. Listings for loadbearing wood stud walls can be used for non-loadbearing cases since the same studs are used in both applications. Loading during the test is critical as it affects the capacity of the wall assembly to remain in place and serve its purpose in preventing fire spread. The strength loss in studs resulting from elevated temperatures or actual burning of structural elements causes deflection. This deflection affects the capacity of the protective wall membranes (gypsum board) to remain in place and contain the fire. The fire-resistance rating of loadbearing wall assemblies is typically lower than that of a similarly designed non-loadbearing assembly. Exterior walls only require rating for fire exposure from within a building. This is because fire exposure from the exterior of a building is not likely to be as severe as that from a fire in an interior room or compartment. Because this rating is required from the inside only, exterior wall assemblies do not have to be symmetrical. The NBC permits the authority having jurisdiction to accept results of fire tests performed according to other standards. Since test methods have changed little over the years, results based on earlier or more recent editions of the CAN/ULC-S101 standard are often comparable. The primary US fire-resistance standard, ASTM E119, is very similar to the CAN/ULC-S101 standard. Both use the same time-temperature curve and the same performance criteria. Fire-resistance ratings developed in accordance with ASTM E119 are usually acceptable to Canadian officials. Whether an authority having jurisdiction accepts the results of tests based on these standards depends primarily on the official’s familiarity with them. Testing laboratories and manufacturers also publish information on proprietary listings of assemblies which describe the materials used and assembly methods. A multitude of fire-resistance tests have been conducted over the last 70 years by North American laboratories. Results are available as design listings or reports through: APA Intertek QAI Laboratories PSF Corporation Underwriters’ Laboratories of Canada Underwriters’ Laboratories Incorporated In addition, manufacturers of construction products publish results of fire-resistance tests on assemblies incorporating their proprietary products (for example, the Gypsum Association’s GA-600 Fire Resistance Design Manual). The NBC contains generic fire-resistance rating information for wood assemblies and members. This includes fire and sound resistance tables describing various wall and floor assemblies of generic building materials that assign specific fire-resistance ratings to the assemblies. Over the last two decades a number of large research projects were conducted at the National Research Council of Canada (NRC) on light-frame wall and floor assemblies, looking at both fire resistance and sound transmission. As a result, the NBC has hundreds of different wall and floor assemblies with assigned fire-resistance ratings and sound transmission ratings. These results are published in the NBC Table A-9.10.3.1.A. Fire and Sound Resistance of Walls and NBC Table A-9.10.3.1.B Fire and Sound Resistance of Floors, Ceilings and Roofs. Not all assemblies described were actually tested. The fire-resistance ratings for some assembles were extrapolated from fire tests done on similar wall assemblies. The listings are useful because they offer off-the-shelf solutions to designers. They can, however, restrict innovation because designers use assemblies which have already been tested rather than pay to have new assemblies evaluated. Listed assemblies must be used with the same materials and installation methods as those tested. The previous section on fire-resistance ratings deals with the determination of fire-resistance ratings from standard tests. Alternative methods for determining fire-resistance ratings are permitted as well. The alternative methods of determining fire-resistance ratings are contained in the NBC, Division B, Appendix D, Fire Performance Ratings. These alternative calculation methods can replace expensive proprietary fire tests. In some cases, these allow less stringent installation and design requirements such as alternate fastener details for gypsum board and the allowance of openings in ceiling membranes for ventilation systems. Section D-2 in NBC, Division B, Appendix D includes methods of assigning fire-resistance ratings to: wood-framed walls, floors and roofs in Appendix D-2.3. (Component Additive Method); solid wood walls, floors and roofs in Appendix D-2.4.; and, glue-laminated timber beams
