Choosing and Applying Exterior Wood Coatings
Choosing a coating depends on what appearance is desired and what level of maintenance would be tolerable. For many people, the basic choice is paint versus stain. The trade-off is often between maintenance frequency and appearance. For many people, additional criteria include VOC emissions, ease of clean up, and cost. See our Links page for web sites and books with detailed information on choosing and applying wood finishes. Read our About exterior wood coatings page for an understanding of the differences between paints and stains, pigmented versus clear coatings, and so forth. Because exterior wood shrinks and swells with moisture changes, the coating needs to be flexible. Flexibility varies by product – some products may be clearly identified as suitably flexible for wood’s dimensional changes. Water-borne coatings are generally more flexible than alkyds. Coatings containing urethanes tend to be more flexible than coatings containing acrylics. For factory finishing with transparent coatings, with special considerations for UV and mildew control, please see our fact sheet Factory Finishing with Transparent Coatings: Requirements for Maximizing Longevity. Special Considerations If a coating is desired for a wear surface such as a deck or stairs, consult carefully with the coating manufacturer to choose the right product for this demanding application. All coatings will be challenged by foot traffic and increased exposure to weather in a horizontal application. High traffic routes will show wear faster than other areas. Paints and other thick film-formers may fail quickly in this situation, and a time-consuming refinishing process will be necessary each time the coating fails. Hence many people will find a stain the more convenient choice for decks and stairs. Knots may require a bit of extra care as some wood extractives or resin may leach out or bleed. Extractive bleeding can cause discolouration, but this can usually be prevented by applying special stain-blocking primers. In some species, especially the pines and Douglas-fir, knots and pitch pockets contain resin. The resin can bleed and may discolour the finish, leave hard beads of resin on the surface, or may otherwise interfere with the coating bond. The best way to prevent this is to purchase kiln-dried wood where the resin should be set (hardened and fixed in place). If painting is desired, choose higher grades of lumber as these will have fewer knots, and choose kiln-dried lumber if using a resinous species. If siding or sidewall shingles are to be painted, the US Forest Products Laboratory (USFPL) recommends they be backprimed. This application of a coating to the back side will plug the wood pores, preventing extractive bleed without blocking water vapour transmission and also preventing liquid water uptake. If possible, round out any sharp corners for best coating adhesion on these edges – for example, a square-edged stair tread will show coating degradation quickly, but bullnosed stair tread edges will retain a coating much longer. This is because a coating applied to a corner tends to pull away from the corner, leaving a much thinner layer there than elsewhere. Surface Preparation Durability of any finish is highly dependent on proper application, which includes good preparation of the surface to be coated. Specific details on surface preparation depend on what condition the wood is to begin with – read on for tips that apply to various scenarios. Surface Preparation for Fresh Wood While fresh, clean wood can be coated without surface preparation, a light sanding with 100 grit sandpaper (and dust removal) can double the service life of some water-based coatings. For best results apply a coating to a fresh wood surface as soon as possible after planing or sanding. If exposed to rain and sun for more than two weeks, adhesion of coatings will not be as good. The surface must also be free of anything that will interfere with coating adhesion, such as dirt, damaged wood fibres and moisture. Grade stamps on wood should also be removed before applying a semitransparent stain, preferably by sanding. Cleaning If there are discolourations caused by dirt, iron stains or other discolourations on the wood surface, cleaning may be desired. It is always preferable to achieve cleaning with sanding when possible. Another safe way to clean wood without damaging the surface is to simply use a garden hose, with or without a pressure nozzle. Use pressure-washing only with extreme care as it can damage wood, especially low-density species such as western red cedar. The pressure should be kept at a minimum, and never hold the nozzle in one place for a long time. If necessary, use a little bit of dish detergent, and lightly scrub (not with steel wool, as this will leave iron stains) in the direction of the grain for any stubborn discolourations. For discolourations that resist soap-and-water cleaning, chemical cleaners will be effective. The chemicals in commercial wood cleaners can be caustic soda (sodium hydroxide), sodium metasilicate, oxalic acid, citric acid, phosphoric acid, borax or some mixture. Wood cleaners containing caustic soda at a 1% – 2% solution will remove nearly all discolourations with the least damage to wood. Some acid cleaners are especially effective for removing extractive stains and iron stain. Bleach is commonly used for cleaning wood, but we do not recommend this, since a poor wood substrate will usually be left behind for subsequent coating. Resin (pine pitch) can be generally removed with mineral spirits. Please note that all acidic or alkaline chemicals need to be thoroughly rinsed off before coating. Chemicals can be toxic, corrosive and harmful, so handle all these chemicals with care and follow all manufacturer’s instructions. Surface Preparation for Aged Wood Wood coatings need a fresh surface or the coating simply won’t last. The longer wood has been allowed to weather, the poorer the coating adhesion. If a fresh surface is allowed to weather or age outdoors for more than two weeks, coating adhesion will deteriorate. This is mainly due to wood damage from sunlight. Weathered wood surfaces usually have a higher acidity, higher contact angle, and lower surface energy. Restoring an aged wood surface is necessary before applying a coating. The damaged (aged/weathered) wood fibres must be removed, exposing fresh wood. Also,
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
Codes & Standards
BUILDING CODES & STANDARDS (THE REGULATORY SYSTEM) The construction industry is regulated through building codes which are informed by: Design standards that provide information on “how to” build with wood, Product standards that define the characteristics of the wood products that can be used in design standards, and Test standards that set out the methodology for establishing a wood product’s characteristics CWC is active in a technical capacity in all areas of the Regulatory System. This includes: BUILDING CODES – CWC participates extensively in the development process of the Building Codes in Canada. CWC is a member of both National and Provincial Building Code Committees. These Committees are balanced and representation is limited to about 25 members on each Committee. Competing interests (i.e. steel and concrete) sit on the same Committees. This is an arena where CWC can win or lose ground for members’ products. DESIGN STANDARDS – Each producer of structural materials develops engineering design standards that provide information on how to use their products in buildings. CWC holds the Secretariat for Canada’s wood design standard (CSA O86 “Engineering Design in Wood”), providing both technical expertise and administrative support for its development. CWC is also a member of the American Wood Council (AWC) committee that is responsible for the U.S. National Design Specification for wood design. PRODUCT STANDARDS – CWC is involved in the development of Canadian, U.S. and international standards for its wood building product producers. TEST STANDARDS – CWC is involved in developing Canadian, U.S. and international test standards in areas that affect wood products, such as fire performance. Detailed building codes & standards pages: Acoustics Combustible construction Encapsulated mass timber construction Energy Code National Fire Code National Model Codes in Canada Wood design in the National Building Code of Canada Wood in non-combustible buildings Wood Standards CSA O86 Engineering design in wood CSA S-6 Canadian Highway Bridge Design Code CSA S406 Permanent Wood Foundations CSA 080 Wood Preservation
Combustible construction
The provision of fire safety in a building is a complex matter; far more complex than the relative combustibility of the main structural materials used in a building. To develop safe code provisions, prevention, suppression, movement of occupants, mobility of occupants, building use, and fuel control are but a few of the factors that must be considered in addition to the combustibility of the structural components. Fire-loss experience shows that building contents play a large role in terms of fuel load and smoke generation potential in a fire. The passive fire protection provided by the fire-resistance ratings on the floor and wall assemblies in a building assures structural stability in a fire. However, the fire-resistance rating of the structural assemblies does not necessarily control the movement of smoke and heat, which can have a large impact on the level of safety and property damage resulting from fire. The National Building Code of Canada (NBC) categorizes wood buildings as ‘combustible construction’. Despite being termed combustible, common construction techniques can give wood frame construction fire-resistance ratings up to two hours. When designed and built to code requirements, wood buildings provide the same level of life safety and property protection required for comparably sized buildings defined under the NBC as ‘noncombustible construction’. Wood has been used for virtually all types of buildings, including; schools, warehouses, fire stations, apartment buildings, and research facilities. The NBC sets out guidelines for the use of wood in applications that extend well beyond the traditional residential and small building sector. The NBC allows wood construction of up to six storeys in height, and wood cladding for buildings designated to be of noncombustible construction. When meeting the area and height limits for the various NBC building categories, wood frame construction can meet the life safety requirements by making use of wood-frame assemblies (usually protected by gypsum wallboard) that are tested for fire-resistance ratings. The allowable height and area restrictions can be extended by using fire walls to break a large building area into smaller separate building areas. The recognized positive contribution to both life safety and property protection which comes from the use of automatic sprinkler systems can also be used to increase the permissible area of wood buildings. Sprinklers typically operate very early in a fire thereby quickly controlling the damaging effects. For this reason, the provision of automatic sprinkler protection within a building greatly improves the life safety and property protection prospects of all buildings including those constructed of noncombustible materials. The NBC permits the use of ‘heavy timber construction’ in buildings where combustible construction is required to have a 45-minute fire-resistance rating. This form of heavy timber construction is also permitted to be used in large noncombustible buildings in certain occupancies. To be acceptable, the components must comply with minimum dimension and installation requirements. Heavy timber construction is afforded this recognition because of its performance record under actual fire exposure and its acceptance as a fire-safe method of construction. In sprinklered buildings permitted to be of combustible construction, no fire-resistance rating is required for the roof assembly or its supports when constructed from heavy timber. In these cases, a heavy timber roof assembly and its supports would not have to conform to the minimum member dimensions stipulated in the NBC. Mass timber elements may also be used whenever combustible construction is permitted. In those instances, however, such mass timber elements need to be specifically designed to meet any required fire-resistance ratings. NBC definitions: Combustible means that a material fails to meet the acceptance criteria of CAN/ULC-S114, “Test for Determination of Non-Combustibility in Building Materials.” Combustible construction means that type of construction that does not meet the requirements for noncombustible construction. Heavy timber construction means that type of combustible construction in which a degree of fire safety is attained by placing limitations on the sizes of wood structural members and on thickness and composition of wood floors and roofs and by the avoidance of concealed spaces under floors and roofs. Noncombustible construction means that type of construction in which a degree of fire safety is attained by the use of noncombustible materials for structural members and other building assemblies. Noncombustible means that a material meets the acceptance criteria of CAN/ULC-S114, “Test for Determination of Non-Combustibility in Building Materials.” For further information, refer to the following resources: National Building Code of Canada CAN/ULC-S114 Test for Determination of Non-Combustibility in Building Materials Wood Design Manual 2017
Connections
As for all other building materials, a critical aspect of wood structures is the manner by which members are connected. Wood products are building materials which are easily drilled, chiseled, or otherwise shaped to facilitate the connection of members, and a number of methods and a wide range of products are available for connecting wood. The installation of metal fasteners is the most common method of connecting wood products and a wide range of hardware is available. These range from the nails and the light connectors used for light framing construction to the bolts, side plates and other hardware used for heavy member connections. Each type of fastener is designed to be used with a particular type of construction. For many applications, such as nailing for light-frame wall construction, metal fasteners serve only a structural purpose, and will be hidden from view by interior and exterior finishes. In other cases where wood members serve a structural purpose and are left exposed to add visual interest to a design and give a robust appearance to a structure, thought must be given to the connection layout and the selection and finishing of the wood products themselves. In other instances, where metal fasteners are exposed to view, the designer might want them to be as inconspicuous as possible. This can be done by selecting fasteners such as split rings and bolts, by reducing the visual impact of hardware through recessing it within the wood members, or by using painting to reduce the prominence of a connection.
Construction Sites
The vulnerability of any building in a fire situation is higher during the construction phase when compared to the susceptibility of the building after it has been completed and occupied. This is because the risks and hazards found on a construction site differ both in nature and potential impact from those in a completed building. And, these risks and hazards are occurring at a time when the fire prevention and protection elements that are designed to be part of the completed building are not yet in place. For these reasons, construction site fire safety includes some unique challenges. However, an understanding of the hazards and their potential risks is the first step towards fire prevention and mitigation. It is important to comply with applicable regulations related to fire safety planning during construction, and cooperation between all stakeholders in establishing and implementing a plan goes a long way in reducing the potential risk and impacts of a fire on any construction sites. In addition to province-wide regulations, local governments and municipalities can also have specific laws, regulations or requirements that must be followed. The local fire department can be a resource in directing you to these additional regulations or requirements. Construction site safety has the potential to impact productivity and profitability at any phase of the project. Given that provincial or municipal regulations provide the minimum requirements for construction site fire safety, consideration should also be given to the specific characteristics, objectives and goals of the project, which could provide incentives to exceed the regulated standards for construction site fire safety. It can be prudent to assess and implement various ‘best practices’, based on the specific needs of your site, which can provide an additional level of protection and build a culture of fire safety. Most construction site fires can be prevented with knowledge, planning and diligence; and, the impact of those fires that might occur can be significantly lessened. Understanding and addressing both the general and specific hazards and risks of a particular construction site requires education and training, as well as preparedness and continued vigilance. For further information, refer to the following resources: “Construction Site Fire Safety: A Guide for Construction of Large Buildings” – by Centre for Public Safety and Criminal Justice Research, University of the Fraser Valley for CWC, 2015 “Construction Site Fire Response: Preventing and Suppressing Fires During Construction of Large Buildings” – by Centre for Public Safety and Criminal Justice Research, University of the Fraser Valley, 2015 “Report on Course of Construction (Fire) Best Practices Guide” – by Technical Risk Services for CWC, 2014 “Comparison of the Canadian Construction Site Fire Safety Regulations/Guidelines” – by Sereca for CWC, 2014 Quick Facts – Insurance and Construction Series (CWC, 2005): “No. 1 – Course of Construction Insurance Basics“ “No. 2 – Course of Construction Risk Control“ “No. 3 – Course of Construction – Site Risk Control Guidelines“ “Fire Safety and Security: A Technical Note on Fire Safety and Security on Construction Sites in British Columbia” – by Wood Works! British Columbia, 2013 City of Surrey, BC – Construction Fire Safety Plan Bulletin Fire Safety During Construction of Five and Six Storey Wood Buildings in Ontario: A Best Practice Guideline – by Ministry of Municipal Affairs and Housing of Ontario, May 2016 “Fire Safety and Security: A Technical Note on Fire Safety and Security on Construction Sites in Ontario” – by Wood Works! Ontario, 2013
Controlling Termites
Fortunately for Canada, most of this country lies north of the limit for termites on the North American continent. However, because termites and people both prefer the warmer parts of this country, 20% of Canada’s population live in areas where termites are present. Long winters limit termite activity in the wild, but the warmth provided by our buildings seems to encourage more serious problems in urban environments. Damage caused by the Eastern subterranean termite, (Reticulitermes flavipes Kollar), has reached economically important levels in areas of Toronto and other cities in Southern Ontario. There are some suggestions that the Western subterranean termite, (Reticulitermes hesperus Banks), may be causing significant damage in the Okanagan region of British Columbia. Termites are a much more serious threat in many of our export markets such as the Southeastern USA, Japan and Southeast Asia. While termite control measures appropriate to each region are specified in local and regional building codes, an overview of such measures may be of use to Canadian marketers of wood products and manufactured homes. Termite control measures can be broadly grouped into six categories: Suppression Site Management Soil Barrier Slab/foundation details Structural durability Surveillance and Remediation Click Here for more details on the 6 strategies More Information Termite Control and Wood-Frame Buildings– 11-page illustrated bulletin from CWC, further covering the 6-point integrated strategy discussed. Includes photos of termite control products. Integrated Control of Subterranean Termites: The 6S Approach. This 20-page Forintek paper introduces and thoroughly discusses the 6-point integrated strategy. Includes very specific design and maintenance advice. Termite Map of North America Combatting Termites – very short and simple summary fact sheet from Forintek.
Cross-Laminated Timber (CLT)
Cross-laminated timber (CLT) is a proprietary engineered wood product that is prefabricated using several layers of kiln-dried lumber, laid flat-wise, and glued together on their wide faces. Panels typically consist of three, five, seven or nine alternating layers of dimension lumber. The alternating directions of the CLT laminations provide it with high dimensional stability. CLT also has a high strength to weight ratio, along with exhibiting advantages for structural, fire, thermal and acoustic performance. Panel thicknesses usually range between 100 to 300 mm (4 to 12 in), but panels as thick as 500 mm (20 in) can be produced. Panel sizes range from 1.2 to 3 m (4 to 10 ft) in width and 5 to 19.5 m (16 to 64 ft) in length. The maximum panel size is limited by the size of the manufacturer’s press and transportation regulations. The design provisions for CLT in Canada apply to sawn lumber panels manufactured in accordance with the ANSI/APA PRG 320 standard. Typically, all the laminations in one direction are manufactured using the same grade and species of lumber. However, adjacent layers are permitted to be of different thickness and made of alternative grades or species. The moisture content of the lumber laminations at the time of CLT manufacturing is between 9 and 15%. There are five primary CLT stress grades; E1, E2, E3, V1 and V2. Stress grade E1 is the most readily available stress grade. The “E” designation indicates machine stress rated (MSR, or E-rated) lumber and the “V” designation indicates visually graded lumber. Stress grades E1, E2 and E3 consist of MSR lumber in all longitudinal layers and visually graded lumber in the transverse layers, while stress grades V1 and V2 consist of visually graded lumber in both longitudinal and transverse layers. Properties for custom CLT stress grades are also published by individual manufacturers. Similar to other proprietary structural wood products, CLT can be evaluated by the Canadian Construction Materials Centre (CCMC) in order to produce a product evaluation report. Unlike primary and custom CLT stress grades which are associated with structural capacity, appearance grades refer to the surface finish of CLT panels. Any stress grade can usually be produced in any surface finish targeted by the designer. Accommodations for reductions in strength and stiffness due to panel profiling or other face- or edge-finishes must be made. The Appendix of ANSI/APA PRG 320 provides examples of CLT appearance classifications. Structural adhesives used in bonding laminations must comply with CSA O112.10 and ASTM D7247 and are also evaluated for heat performance during exposure to fire. The different classes of structural adhesives that are typically used include: Emulsion polymer isocyanate (EPI); One-component polyurethane (PUR); Phenolic types such as phenol-resorcinol formaldehyde (PRF). Since pressure treatment with water-borne preservatives can negatively affect bond adhesion, CLT is not permitted to be treated with water-borne preservatives after gluing. For CLT treated with fire-retardant or other potentially strength-reducing chemicals, strength and stiffness is required to be based on documented test results. As part of the prefabrication process, CLT panels are cut to size, including door and window openings, with state-of-the art computer numerical controlled (CNC) routers, capable of making complex cuts with low tolerances. Prefabricated CLT elements arrive on site ready for immediate installation. CLT offers design flexibility and low environmental impacts for floor, roof and wall elements within innovative mid-rise and tall wood buildings. For further information on CLT, refer to the following resources: Kalesnikoff Nordic Structures APA – The Engineered Wood Association Canadian Construction Materials Centre (CCMC) Element5 ANSI/APA PRG 320 Standard for Performance-Rated Cross-Laminated Timber CSA O86 Engineering design in wood CSA O112.10 Evaluation of Adhesives for Structural Wood Products (Limited Moisture Exposure) ASTM D7247 Standard Test Method for Evaluating the Shear Strength of Adhesive Bonds in Laminated Wood Products at Elevated Temperatures
CSA 080 Wood Preservation
The National Building Code of Canada (NBC) contains requirements regarding the use of treated wood in buildings and the CSA O80 Series of standards is referenced in the NBC and in provincial building codes for the specification of preservative treatment of a broad range of wood products used in different applications. The first edition of CSA O80 was published in 1954, with eleven subsequent revisions and updates to the standard, with the most recent edition published in 2015. The manufacture and application of wood preservatives are governed by the CSA O80 Series of standards. These consensus-based standards indicate the wood species that may be treated, the allowable preservatives and the retention and penetration of preservative in the wood that must be achieved for the use category or application. The CSA O80 Series of standards also specifies requirements related to the fire retardance of wood through chemical treatment using both pressure and thermal impregnation of wood. The overarching subjects covered in the CSA O80 Series of standards also include materials and their analysis, pressure and thermal impregnation procedures, and fabrication and installation. Canadian standards for wood preservation are based on the American Wood Protection Association (AWPA) standards, modified for Canadian conditions. Only wood preservatives registered by the Canadian Pest Management Regulatory Agency are listed. The required preservative penetrations and loadings (retentions) vary according to the exposure conditions a product is likely to encounter during its service life. Each type of preservative has distinct advantages and the preservative used should be determined by the end use of the material. Processing and treating requirements in the CSA O80 Series are designed to assess the exposure conditions which pressure treated wood will be subjected to during the service life of a product. The level of protection required is determined by hazard exposure (e.g., climatic conditions, direct ground contact or exposure to salt water), the expectations of the installed product (e.g., level of structural integrity throughout the service life) and the potential costs of repair or replacement over the life cycle. The technical requirements of CSA O80 are organized in the Use Category System (UCS). The UCS is designed to facilitate selection of the appropriate wood species, preservative, penetration, and retention (loading) by the specifier and user of treated wood by more accurately matching the species, preservative, penetration, and retention for typical moisture conditions and wood biodeterioration agents to the intended end use. The CSA O80.1 Standard specifies four Use Categories (UC) for treated wood used in construction: UC1 covers treated wood used in dry interior construction; UC2 covers treated wood and wood-based materials used in dry interior construction that are not in contact with the ground but can be exposed to dampness; UC3 covers treated wood used in exterior construction that is not in ground contact; UC3.1 covers exterior, above ground construction with coated wood products and rapid run off of water; UC3.2 covers exterior, above ground construction with uncoated wood products or poor run off of water; UC4 covers treated wood used in exterior construction that is in ground or freshwater contact; UC4.1 covers non-critical components; UC4.2 covers critical structural components or components that are difficult to replace; UC5A covers treated wood used in Coastal waters including; brackish water, salt water and adjacent mud zone. This CSA O80 Series of standards consists of five standards, as follows: CSA O80.0 General requirements for wood preservation; specifies requirements and provides information applicable to the entire series of standards. CSA O80.1 Specification of treated wood; is intended to help specifiers and users of treated wood products identify appropriate requirements for preservatives for various wood products and end use environments. CSA O80.2 Processing and treatment; specifies minimum requirements and process limitations for treating wood products. CSA O80.3 Preservative formulations; specifies requirements for preservatives not referenced elsewhere. CSA O80.4 has been withdrawn. CSA O80.5 CCA Additives — Utility Poles; specifies requirements for preparation and use of CCA preservative/additive combinations for utility poles permitted by CSA O80.1 and CSA O80.2. For further information, refer to the following resources: www.durable-wood.com CSA O80 Wood preservation Wood Preservation Canada National Building Code of Canada Pest Management Regulatory Agency American Wood Protection Association ISO 21887 Durability of wood and wood-based products — Use classes
CSA O86 Engineering design in wood
CSA O86 Engineering design in wood The National Building Code of Canada (NBC) contains requirements regarding the engineering design of structural wood products and systems. The CSA O86 standard is referenced in Part 4 of the NBC and in provincial building codes for the engineered design of structural wood products. The first edition of CSA O86 was published in 1959. CSA O86 provides criteria for the structural design and evaluation of wood structures or structural elements. It is written in the limit states design (LSD) format and provides resistance equations and specified strength values for structural wood products, including: graded lumber, glued-laminated timber, cross-laminated timber (CLT), unsanded plywood, oriented strandboard (OSB), composite building components, light-frame shearwalls and diaphragms, timber piling, pole-type construction, prefabricated wood I-joists, structural composite lumber (SCL) products, permanent wood foundations (PWF), and their structural connections. The CSA O86 provides rational approaches for structural design checks related to ultimate limit states, such as flexure, shear, and bearing, as well as serviceability limit states, such as deflection and vibration. The CSA O86 also contains strength modification factors for behaviour related to duration of load, size effects, service condition, lateral stability, system effects, preservative and fire-retardant treatment, notches, slenderness, and length of bearing. Structural design of wood buildings and components is undertaken using the loads defined in Part 4 of the NBC and the material resistance values obtained using the CSA O86 standard. Housing and other small buildings can be built without a full structural design using the prescriptive requirements outlined in Part 9 ‘Housing and Small Buildings’ of the NBC. For further information, refer to the following resources: Wood Design Manual (Canadian Wood Council) Introduction to Wood Design (Canadian Wood Council) National Building Code of Canada CSA O86 Engineering design in wood
CSA S-6 Canadian Highway Bridge Design Code
As identified in the design philosophy of the CSA S-6, safety is the overriding concern in the design of highway bridges in Canada. For wood products, the CSA S-6 addresses design criteria associated with ultimate limit states and serviceability limit states (primarily deflection, cracking, and vibration). Fatigue limit states are also required to be consider for steel connection components in wood bridges. The structure design life in the CSA S-6 has been established at 75 years for all bridge types, including wood bridges. The CSA S-6 applies to the types of wood structures and components likely to be required for highways, including; glued-laminated timber, sawn lumber, structural composite lumber (SCL), nail-laminated decks, laminated wood-concrete composite decks, prestressed laminated decks, trusses, wood piles, wood cribs and wood trestles. The standard does not apply to falsework or formwork. CSA S-6 considers design of wood members under flexure, shear, compression and bearing. In addition, the standard provides guidance and requirements related to the camber and curvature of wood members. Further information on durability, drainage and preservative treatment of wood in bridges is also discussed.
CSA S406 Permanent Wood Foundations
CSA S406 Specification of permanent wood foundations for housing and small buildings CSA S406 is the design and construction standard for permanent wood foundations (PWF) that is referenced in Part 9 of the NBC and in provincial building codes. The first edition of CSA S406 was published in 1983, with subsequent revisions and updates to the standard published in 1992, 2014, and 2016. The CSA S406 applies to the selection of materials, the design, the fabrication and installation of PWF. The standard also contains information on site preparation, materials, cutting and machining, footings, sealants and dampproofing, exterior moisture barriers, backfilling and site grading. Specific details and prescriptive requirements are provided in CSA S406 for buildings constructed on PWF that fall under Part 9 of the National Building Code of Canada (NBC), that is, buildings up to three-storeys in height above the foundation and having a building area not exceeding 600 m2. CSA S406 provides for the optional use of wood sleeper, poured concrete slab, and suspended wood basement floor systems as components of the PWF, and for the use of PWF as crawl space enclosures. The standard does not exclude PWFs which may also be engineered for larger buildings, using the same principles of design, provided building code requirements are met. The CSA S406 standard includes many selection tables and isometric figures, aimed at increasing design efficiency and the understanding of PWF construction details. The standard was developed based on specific engineering design assumptions regarding installation procedures, soil type, clear spans for floors and roofs, dead and live loads, modification factors, deflections and backfill height. For conditions that go beyond the scope of CSA S406, similar details may be used provided they are based on accepted engineering principles that ensure a level of performance equivalent to that set forth in CSA S406. If any of the design conditions are different from or more severe than the assumptions, the PWF must be designed by a professional engineer or architect and installed in conformance with the standard. Regardless of the building size and conformance with the design assumptions of CSA S406, some authorities having jurisdiction require a design professional’s seal in order to issue a building permit. For further information, refer to the following resources: Permanent Wood Foundations (Canadian Wood Council) Wood Preservation Canada National Building Code of Canada
