Treatability
Treatability of Major North American Softwoods Some wood is easier to treat than others. The particular structure of the cells for a given piece of wood will determine how permeable the wood is to chemicals. This table describes the permeability of common softwoods used in North America. The permeability ratings are: 1 – Permeable 2 – Moderately Impermeable 3 – Impermeable 4 – Extremely Impermeable Tree Permeability Permeability Predominant in the Tree Sapwood Heartwood Douglas Fir 2 4 Heartwood Western Hemlock 2 3 Heartwood Eastern Hemlock 2 4 Heartwood White Spruce 2 3-4 Heartwood Engelmann Spruce 2 3-4 Heartwood Black Spruce 2 4 Heartwood Red Spruce 2 4 Heartwood Sitka Spruce 2 3 Heartwood Lodgepole Pine 1 3-4 Heartwood Jack Pine 1 3 Heartwood Red Pine 1 3 Sapwood Southern Pine 1 3 Sapwood Ponderosa Pine 1 3 Sapwood Amabilis Fir (Pacific silver fir) 2 2-3 Heartwood Alpine Fir 2 3 Heartwood Balsam Fir 2 4 Heartwood Western Red Cedar 2 3-4 Heartwood Eastern White Cedar 2 3-4 Heartwood Yellow Cypress 1 3 Heartwood Western S-P-F 2 3-4 Heartwood Eastern S-P-F 2 4 Heartwood Hem-Fir 2 3 Heartwood Western Larch 2 4 Heartwood Tamarack 2 4 Heartwood Incising We can improve the penetration of preservative into impermeable wood by making little cuts in the wood. A series of small, shallow slits are cut into the wood by an incising machine. This is an effective way of increasing the treatability of lumber pieces which are predominantly heartwood. Species with heartwood permeability ratings of higher than 3 require high density incising (over 7,500 incisions per square meter). Incising does reduce the strength of lumber and this effect must be taken into account in engineering calculations. Drying to Maximise Treatabilty Unless the purchaser can be assured that lumber for treatment will be air dried to less than 30% moisture content, the specification of KD lumber for preservative treatment is strongly recommended. The problem with treating lumber which is not kiln dried is that the practicalities of production and delivery lead to the potential for poor product quality. The durability of treated Canadian lumber relies on a shell of preservative treatment preventing access by wood-rotting fungi to the untreated core. If the treated shell fails to prevent penetration by checks or abrasion or if the wood-rotting fungus is already in the untreated core, premature failure can result. There are four major pitfalls in treating green lumber: saturated sapwood, frozen lumber, check development and pre-treatment infection. Saturated Sapwood In order for the preservative to penetrate the wood cells, they must be empty of water, that is, the wood must be below 30% moisture content. In green lumber the sapwood cells may be too full of sap to accept any preservative. The sapwood is the part most susceptible to decay and most in need of preservative penetration. Partial air or kiln drying to between 20 and 30% moisture content is ideal, but there is seldom the time or the conditions necessary to do this. Purchasing commercial KD material (maximum 20%) is normally the only option to ensure the sapwood will accept treatment. Frozen Lumber The overwhelming majority of production is treated over the winter to prepare for the spring and summer outdoor construction season. With the exception of coastal British Columbia, most regions of Canada will be dealing with frozen wood at this time. Many treating plants do not have dry kilns, thus material is treated in the condition it is delivered to the plant. Preservative will not penetrate through ice until it is fully thawed. This typically occurs in contact with the treating solution. Frozen green lumber contains a lot of ice and there is insufficient time for this to thaw during typical commercial treating cycles. The residual moisture (12 – 20%) in kiln-dried lumber is in the cell walls and will not impede preservative penetration even if it is frozen. Check Development Checks only develop when the moisture content of wood drops below about 28%. If lumber is treated green and then dries, checks will penetrate the treated zone exposing the untreated core. If lumber is kiln-dried to the in-service moisture content, typically around 16% in exterior exposure, the checks will be largely developed prior to treatment. This means that the checks will be lined with a treated zone and the shell of treatment will remain intact. Pre-treatment Infection A lesser problem than the above three, but still of some concern, is the potential for survival through the manufacturing process of wood-rotting fungi that may have infected in the tree, log or lumber storage stages. At worst, this might only apply to 10% or fewer of pieces. Nevertheless, we have seen examples where treatment of green lumber without application of heat (60°C or more) fails to kill wood-rotting fungi already in the product, leading to premature failure in service. This can occur in as little as 4 years. CCA treatment is a cool process, but most kiln-drying schedules will kill all wood-rotting fungi.
Resilience
Individuals in the design and construction community are increasingly choosing materials, design techniques and construction procedures that improve a structure’s ability to withstand and recover from extreme events such as intense rain, snow and wind, hurricanes, earthquakes and wildfire. As a result, specifying robust materials and design details, and constructing flexible and easily repairable buildings are becoming important design criteria. Resilience is the ability to prepare and plan for, absorb, recover from, and more successfully adapt to adverse events. For a building, this means being designed to withstand and recover quickly from adverse situations such as flooding and high winds, with an acceptable level of functionality. A structure built to withstand such natural disasters with minimal damage is easier to repair and can contribute to sustainable development. Designing for resilience can contribute to minimizing human risk, reducing material waste and lowering restoration costs. As a result of shifting weather patterns due to climate change, there is a growing interest in adaptation and designing for resilience. Higher temperatures can increase the odds of more extreme weather events, including severe heat waves and regional changes in floods, droughts and potential for more severe wildfires. There are more intense and more frequent hurricanes, and precipitation often comes in the form of intense single-day events. Warmer winter temperatures cause water to evaporate in the air and if the temperature is still below freezing, this can lead to unusually heavy snow, sleet or freezing rain, even in years when snowfall is lower than average. A resilient building is able to deal with changes such as a heavier snow load, wider temperature fluctuations, and more extreme wind and rain. Existing wood buildings can be easily adapted or retrofitted if there is a need for increased wind or snow loading. Wood buildings that are properly designed and constructed perform well in all types of climates, even the wettest. Wood tolerates high humidity and can absorb or release water vapour without compromising the structural integrity. In some regions, climate change is seen to be contributing to increasingly complex wildfire seasons, which results in greater risk of extreme wildfire events. Some wildland fire regulations target specific construction features in wildland-urban interface areas, such as exterior decks, roof coverings, and cladding. A number of wood products meet these regulations for various applications, including heavy timber elements, fire retardant treated wood and some wood species that demonstrate low flame spread ratings (less than 75). For further information, refer to the following resources: Resilient and Adaptive Design Using Wood (Canadian Wood Council) American Wood Council American Institute of Architects
Remedial Treatment
Since remedial treatment is intended to solve a known insect or decay problem, the first thing to do is investigate the extent of the problem and, if necessary, provide temporary structural support. The investigation phase should also identify the causal factors so that these can be eliminated, where possible. Also during the investigation, the parts of the wood that have lost strength may be removed. Be aware that a wood decay fungus may have penetrated well beyond the boundaries of the visibly rotted wood. Since deterioration is underway, a rapid response is normally required. This means that where the deteriorated and infected wood cannot be removed and replaced with sound wood, the remedial treatment must be capable of rapidly penetrating the wood and killing the fungi or insects. Solids Since solids take time to dissolve and move, they are commonly supplemented by liquid treatments for more rapid eradication of the decay fungus or insect. Borate and copper/borate rods are the only solid remedial treatment method available to the homeowner. Liquids, Pastes and Gels Liquids, pastes and gels work rapidly as they do not have to rehydrate or dissolve to start moving and working. Since all visibly decayed wood should be removed wherever possible, these treatments are often used primarily to kill and contain any residual infection inadvertently left behind. Brush or spray applications are quite appropriate for this use. Gels are commonly applied to paint cracks in window joints and to the bottom of door frames, locations where moisture may get into the wood. Where decayed wood is present inside poles and timbers and cannot be removed, liquids, pastes or gels must be inserted deep into the wood for rapid action. Fumigants Gases move the most rapidly and therefore have a faster eradicant action.
Moisture and Wood
The durability of wood is often a function of water, but that doesn’t mean wood can never get wet. Quite the contrary, wood and water usually live happily together. Wood is a hygroscopic material, which means it naturally takes on and gives off water to balance out with its surrounding environment. Wood can safely absorb large quantities of water before reaching moisture content levels that will be inviting for decay fungi. Moisture content (MC) is a measure of how much water is in a piece of wood relative to the wood itself. MC is expressed as a percentage and is calculated by dividing the weight of the water in the wood by the weight of that wood if it were oven dry. For example, 200% MC means a piece of wood has twice as much of its weight due to water than to wood. Two important MC numbers to remember are 19% and 28%. We tend to call a piece of wood dry if it is at 19% or less moisture content. Fiber saturation averages around 28%. Fiber saturation is an important benchmark for both shrinkage and for decay. The fibers of wood (the cells that run the length of the tree) are shaped like tapered drinking straws. When fibers absorb water, it first is held in the cell walls themselves. When the cell walls are full, any additional water absorbed by the wood will now go to fill up the cavities of these tubular cells. Fiber saturation is the level of moisture content where the cell walls are holding as much water as they can. Water held in the cell walls is called bound water, while water in the cell cavities is called free water. As the name implies, the free water is relatively accessible, and an accessible source of water is one necessity for decay fungi to start growing. Therefore, decay can generally only get started if the moisture content of the wood is above fiber saturation. The fiber saturation point is also the limit for wood shrinkage. Wood shrinks or swells as its moisture content changes, but only when water is taken up or given off from the cell walls. Any change in water content in the cell cavity will have no effect on the dimension of the wood. Therefore, wood only shrinks and swells when it changes moisture content below the point of fiber saturation. Like other hygroscopic materials, wood placed in an environment with stable temperature and relative humidity will eventually reach a moisture content that yields no vapor pressure difference between the wood and the surrounding air. In other words, its moisture content will stabilize at a point called the equilibrium moisture content (EMC). Wood used indoors will eventually stabilize at 8-14% moisture content; outdoors at 12-18%. Hygroscopicity isn’t necessarily a bad thing – this allows wood to function as a natural humidity controller in our homes. When the indoor air is very dry, wood will release moisture. When the indoor air is too humid, wood will absorb moisture. Wood shrinks/swells when it loses/gains moisture below its fiber saturation point. This natural behaviour of wood is responsible for some of the problems sometimes encountered when wood dries. For example, special cracks called checks can result from stresses induced in a piece of wood that is drying. As the piece dries, it develops a moisture gradient across its section (dry on the outside, wet on the inside). The dry outer shell wants to shrink as it dries below fiber saturation, however, the wetter core constrains the shell. This can cause checks to form on the surface. The shell is now set in its dimension, although the core is still drying and will in turn want to shrink. But the fixed shell constrains the core and checks can thus form in the core. Another problem associated with drying is warp. A piece of wood can deviate from its expected shape as it dries due to the fact that wood shrinks different amounts in different directions. It shrinks the most in the direction tangential to the rings, about half as much in the direction perpendicular to the rings, and hardly at all along the length of the tree. Where in the log a piece was cut will be a factor in how it changes shape as it shrinks. One advantage of usingdry lumber is that most of the shrinkage has been achieved prior to purchase. Dry lumber is lumber with a moisture content no greater than 19%; wood does most of its shrinking as it drops from 28-19%. Dry lumber will have already shown its drying defects, if any. It will also lead to less surprises in a finished building, as the product will stay more or less at the dimension it was upon installation. Dry lumber will be stamped with the letters S-DRY (for surfaced dry) or KD (for kiln dry). Another way to avoid shrinkage and warp is to use composite wood products, also called engineered wood products. These are the products that are assembled from smaller pieces of wood glued together – for example, plywood, OSB, finger-jointed studs and I-joists. Composite products have a mix of log orientations within a single piece, so one part constrains the movement of another. For example, plywood achieves this crossbanding form of self-constraint. In other products, movements are limited to very small areas and tend to average out in the whole piece, as with finger-jointed studs.
Decay
Wood is biodegradable – that’s a characteristic we normally consider to be one of the benefits of choosing natural materials. Organisms exist that can break down wood into its basic chemicals so that fallen logs in the forest can contribute to the growth of the next generation of life. This process – essential in the forest – must be prevented when we use wood in buildings. A variety of fungi, insects, and marine borers have the capability to break down the complex polymers which make up the wood structure. In Canada, fungi are a more serious problem than insects. The wood-inhabiting fungi can be separated into moulds, stainers, soft-rot fungi and wood-rotting basidiomycetes. The moulds and stainers can discolour the wood however they do not significantly damage the wood structurally. Soft-rot fungi and wood-rotting basidiomycetes can cause strength loss in wood, with the basidiomycetes the ones responsible for decay problems in buildings. With regard to insects, carpenter ants only cause problems in decayed wood, and significant subterranean termite activity is confined to a few southern areas of Canada. However, other parts of the world have a serious problem with termites. Decayed wood is the result of a series of events including a sequence of fungal colonization. The spores of these fungi are ubiquitous in the air for much of the year. Wood-rotting fungi require wood as their food source, an equable temperature, oxygen and water. Water is normally the only one of these factors that we can easily manage. This may be made more difficult by some fungi, which can transport water to otherwise dry wood. It can also be difficult to control moisture once decay has started, since the fungi produce water as a result of the decay process. The outer portion of this log is being attacked by a decay fungus. Note that the damage is held back at the line between heartwood and sapwood. To understand why, click here to read about natural durability. More Information Click Here for a 26-page paper on biodeterioration, including illustrations and bibliography. For answers to common questions on decay, visit the FAQ page
Termites
Termites, sometimes called “white ants” are a social insect, more closely related to cockroaches than ants. They can be distinguished from ants by the absence of a narrow waist on the body and their typically white colour. Under a hand lens, termite antennae are straight whereas those of ants have an elbow. Flying reproductive termites (alates) can be distinguished from flying ants by the equal size of all four termite wings. Three types of termites can be distinguished on the basis of their moisture requirements: Damp-wood termites Dry-wood termites Subterranean termites Damp-wood termites are particularly prevalent in coastal British Columbia and the Pacific Northwest of the USA. They only attack and help physically break down decaying trees in forest ecosystems and can be controlled by eliminating the moisture source which has led to decay. They are rarely a problem in buildings. Dry-wood termites on the other hand pose significant hazards to exposed, accessible wooden infrastructure, since they need no significant moisture source, and mated pairs can fly into buildings and start up a nest in dry wood. Consequently, control measures designed to separate wood from soil or moisture are ineffective. On the North American Continent, dry-wood termites are found only from the extreme south of the USA into Mexico. Subterranean termites do need a reliable source of moisture, normally the soil, but they have the capability to carry their required moisture needs into dry wood in buildings. Although satellite nests can occur in buildings, their main nests are normally in soil or wood in contact with soil. Subterranean termites build characteristic shelter-tubes (tunnels) of mud, wood fragments and bodily secretions, which allow them to pass from the soil to wood above ground without being exposed to drying air or predators. These shelter tubes can extend for several metres over inert substrates, such as concrete foundation walls. Termites can also pass through cracks in concrete as narrow as 1.5 mm. Within the subterranean group, one particular species: the Formosan termite (Coptotermes formosanus Shiraki), is the most problematic for wooden infrastructure. Although individuals are smaller than the species mentioned above, because of sheer numbers Formosan termite colonies can be nine times more aggressive in terms of wood consumption. This species is particularly problematic in parts of Southeastern USA, particularly Florida, where it was introduced after WWII. It is unlikely to spread north into Canada although Canada does have other, less-aggressive species of subterranean termites. Subterranean termites are the most economically important group worldwide. More Information Click here for a termite map of Canada. Click here for a termite map of SW Ontario. Click here for a termite map of British Columbia. Additional Sources of Information on Termites Louisiana State University Agricultural Center City of Guelph Municipality of Kincardine
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.
Applying Treatment
Holes drilled to apply depot, supplementary or remedial treatments should be on vertical surfaces or undersides, where possible, to avoid creating additional routes for moisture entry. In the case of supplementary treatment, cut ends should be placed so they are not in ground contact where possible. Holes for treatment should not be drilled below ground level if it can possibly be avoided. All holes should be closed with a tight-fitting plug. Ideally this should be removable to allow re-treatment. Holes for water-soluble treatments should be placed in the right locations to intercept moisture close to its points of entry. Look carefully at the structure and think about moisture sources, water traps, moisture entry points, moisture flow and signs of moisture entry. Moisture sources include direct rainfall, diverted rainfall (via windows, cladding, balcony and walkway surfaces, roof overhangs, flashing, parapets, eavestroughs and downspouts), rain penetration of moisture barriers via nail holes, splits, failure of joints or deterioration of caulking, rain splash, blowing snow, ice dams, condensation, concrete foundations, soil contact, irrigation systems, drain and plumbing leaks. Water traps include metal “shoes”, V joints, checks, appressed boards, cupped horizontal surfaces and anywhere a rim is created at the edge of a horizontal surface. Accumulation of dirt and debris often indicates a water trap. Growth of algae also indicates locations where moisture hangs around longer after rain. Moisture entry points include all locations with end grain, around nails, screws and bolts plus any other holes or penetrations, checks and delaminations. Moisture flow in wood may be 100 to 1000 times faster along than across the grain. Patterns of moisture distribution in wood are therefore commonly elongated cones or lens shapes centred on the point of entry. Signs of moisture entry include swelling, darker colouration, fungal stain, iron stain around fasteners, nail popping and flaking of film-forming surface finishes. Confirmation of moisture contents conducive to decay can be made using electrical-resistance type moisture meters. Capacitance-type moisture meters may also be useful, but these can give erroneous results in the area of metal fittings. Click Here for more information of field treatment
Grades
Visual grading of dimension lumber In Canada, we are fortunate to have forests that are capable of producing dimension lumber that is desirable for use as structural wood products. Some primary factors that contribute to the production of lumber that is desirable for structural uses include; a favourable northern climate that is conducive to tree growth, many Canadian species contain small knots, and many of the Western Canadian species grow to heights of thirty meters or more, providing long sections of clear knot free wood and straight grain. The majority of the structural wood products are grouped within the spruce-pine-fir (S-P-F) species combination, which has the following advantages for structural applications: straight grain good workability light weight moderate strength small knots ability to hold nails and screws There are more than a hundred softwood species in North America. To simplify the supply and use of structural softwood lumber, species having similar strength characteristics, and typically grown in the same region, are combined. Having a smaller number of species combinations makes it easier to design and select an appropriate species and for installation and inspection on the job site. In contrast, non-structural wood products are graded solely on the basis of appearance quality and are typically marked and sold under an individual species (e.g., Eastern White Pine, Western Red Cedar). Canadian dimension lumber is manufactured in accordance with CSA O141 Canadian Standard Lumber and must conform to the requirements of the Canadian and US lumber grading rules. Each piece of dimension lumber is inspected to determine its grade and a stamp is applied indicating the assigned grade, the mill identification number, a green (S-Grn) or dry (S-Dry) moisture content at time of surfacing, the species or species group, the grading authority having jurisdiction over the mill of origin, and the grading rule used, where applicable. Dimension lumber is generally grade stamped on one face at a distance of approximately 600 mm (2 ft) from one end of the piece, in order to ensure that the stamp will be clearly visible during construction. Specialty items, such as lumber manufactured for millwork or for decorative purposes, are seldom marked. To ensure this uniform quality of dimension lumber, Canadian mills are required to have each piece of lumber graded by lumber graders who are approved by an accredited grading agency. Grading agencies are accredited by the CLSAB. NLGA Standard Grading Rules for Canadian Lumber provide a list of the permitted characteristics within each grade of dimension lumber. The grade of a given piece of dimension lumber is based on the visual observations of certain natural characteristics of the wood. Most softwood lumber is assigned either an appearance grade or a structural grade based on a visual review performed by a lumber grader. The lumber grader is an integral part of the lumber manufacturing process. Using established correlations between appearance and strength, lumber graders are trained to assign a strength grade to dimensional lumber based on the presence or absence of certain natural characteristics. Examples of such characteristics include; the presence of wane (bark remnant on the outer edge), size and location of knots, the slope of the grain relative to the long axis and the size of shakes, splits and checks. Other characteristics are limited by the grading rules for appearance reasons only. Some of these include sap and heart stain, torn grain and planer skips. The table below shows a sample of a few of the criteria used to assess grades for 2×4 dimensional lumber that is categorized as ‘structural light framing’ or as ‘structural joist and plank’. Grades Characteristic Select Structural No.1 & No. 2 No. 3 Edge of wide face knots ¾” 1 ¼” 1 ¾” Slope of grain 1 in 12 1 in 8 1 in 4 To keep sorting cost to a minimum, grades may be grouped together. For example, there is an appearance difference between No.1 and No.2 visually graded dimension lumber, but not a difference in strength. Therefore, the grade mark ‘No.2 and better’ is commonly used where the visual appearance of No.1 grade dimensional lumber is not required, for example, in the construction of joists, rafters or trusses. Pieces of the same grade must be bundled together with the engineering properties dictated by the lowest strength grade in the bundle. Dimension lumber is aggregated into the following four grade categories: Structural light framing, Structural joists and planks, Light framing, and Stud. The table below shows the grades and uses for these categories. Grade Category Size Grades Common Grade Mix Principal Uses Structural Light Framing 38 to 89mm (2″ to 4″ nom.) thick and wide Select Structural, No.1, No.2, No.3 No.2 and Better Used for engineering applications such as for trusses, lintels, rafters, and joists in the smaller dimensions. Structural Joists and Planks 38 to 89mm (2″ to 4″ nom.) thick and 114mm (5″ nom.) or more wide Select Structural, No.1, No.2, No.3 No.2 and Better Used for engineering applications such as for trusses, lintels, rafters, and joists in the dimensions greater than 114mm (5″ nom.). Light Framing 38 to 89mm (2″ to 4″ nom.) thick and wide Construction, Standard, Utility Standard and Better (Std. & Btr.) Used for general framing where high strength values are not required such as for plates, sills, and blocking. Studs 38 to 89mm (2″ to 4″ nom.) thick and 38 to 140mm (2″ to 6″ nom.) wide and 3m (10′) or less in length Stud, Economy Stud Made principally for use in walls. Stud grade is suitable for bearing wall applications. Economy grade is suitable for temporary applications. Notes: Grades may be bundled individually or they may be individually stamped, but they must be grouped together with the engineering properties dictated by the lowest strength grade in the bundle. The common grade mix shown is the most economical blending of strength for most applications where appearance is not a factor and average strength is acceptable. Except for economy grade, all grades are stress graded, meaning specified strengths have been
Canadian Species
Canadian species of visually graded lumber There are more than a hundred softwood species in North America. To simplify the supply and use of structural softwood lumber, species having similar strength characteristics, and typically grown in the same region, are combined. Having a smaller number of species combinations makes it easier to design and select an appropriate species and for installation and inspection on the job site. In contrast, non-structural wood products are graded solely on the basis of appearance quality and are typically marked and sold under an individual species (e.g., Eastern White Pine, Western Red Cedar). The Spruce-Pine-Fir (S-P-F) species group grows abundantly throughout Canada and makes up by far the largest proportion of dimension lumber production. The other major commercial species groups for Canadian dimension lumber are Douglas Fir-Larch, Hem-Fir and Northern Species. The four species groups of Canadian lumber and their characteristics are shown below. Species Combination: Douglas Fir-Larch Abbreviation: D.Fir-L or DF-L Species Included in Combination Growth Region Douglas Fir Western Larch Characteristics Colour Ranges Reddish brown to yellow High degree of hardness Good resistance to decay Species Combination: Hem-Fir Abbreviation: Hem-Fir or H-F Species Included in Combination Growth Region Pacific Coast Hemlock Amabilis Fir Characteristics Colour Ranges Yellow brown to white Works easily Takes paint well Holds nails well Good gluing characteristics Species Combination: Spruce-Pine-Fir Abbreviation: S-P-F Species Included in Combination Growth Region White Spruce Engleman Spruce Red Spruce Black Spruce Jack Pine Lodgepole Pine Balsam Fir Alpine Fir Characteristics Colour Ranges White to pale yellow Works easily Takes paint well Holds nails well Good gluing charateristics Species Combination: Northern Species Abbreviation: North or Nor Species Included in Combination Growth Region Western Red Cedar Characteristics Colour Ranges Reddish brown heartwood, light sapwood Exceptional resistance to decay Moderate strength High in appearance qualities Works easily Takes fine finishes Lowest shrinkage Also Included in Northern Species Species Included in Combination Growth Region Red Pine Characteristics Colour Ranges Works easily Also Included in Northern Species Species Included in Combination Growth Region Ponderosa Pine Characteristics Colour Ranges Takes finishes well Holds nails well Holds screws well Seasons with little checking or cupping Also Included in Northern Species Species Included in Combination Growth Region Western White Pine Eastern White Pine Characteristics Colour Ranges Creamy white to light straw brown heartwood, almost white sapwood Works easily Finishes well Doeasnât tend to split or splinter Holds nails well Low shrinkage Takes stain, paints & varnishes well Also Included in Northern Species Species Included in Combination Growth Region Trembling Aspen Largetooth Aspen Balsam Poplar Characteristics Colour Ranges Works easily Finishes well Holds nails well Below is a map of the forest regions in Canada and the principal tree species that grow in each region. Click to enlarge the map. This map appears courtesy of Natural Resources Canada.
Adhesives
Adhesives can also be referred to as resins. Many engineered wood products, including finger-joined lumber, plywood, oriented strand board (OSB), glulam, cross-laminated timber (CLT), wood I-joists and other structural composite lumber products, require the use of adhesives to transfer the stresses between adjoining wood fibres. Waterproof adhesives and heat resistant adhesives are commonly used in the manufacture of structural wood products. Advances in adhesive technology to address challenges associated with increased production rates, visual appearance, process emissions and environmental impact concerns, have resulted in a wider range of innovative structural adhesive products. It is imperative that this new generation of adhesives achieve the same level of performance as traditional structural wood product adhesives such as phenol-formaldehyde (PF) or phenol-resorcinol formaldehyde (PRF). Examples of different structural wood product adhesives families include, but are not limited to: Emulsion polymer isocyanate (EPI); One-component polyurethane (PUR); Phenolic resins such as phenol-formaldehyde (PF) and phenol-resorcinol formaldehyde (PRF). Various types of extenders such as walnut shell flour, Douglas fir bark flour, alder bark flour, and wood flour are sometimes used to reduce cost, control penetration into the wood fibre or moderate strength properties for the specific materials being bonded. There are several industry standards that may be used to evaluate the performance of structural wood product adhesives, including: CSA O112.6 Phenol and phenol-resorcinol resin adhesives for wood (high-temperature curing) CSA O112.7 Resorcinol and phenol-resorcinol resin adhesives for wood (room- and intermediate-temperature curing) CSA O112.9 Evaluation of adhesives for structural wood products (exterior exposure) CSA O112.10 Evaluation of adhesives for structural wood products (limited moisture exposure) CAN/CSA O160 Formaldehyde emissions standard for composite wood products ASTM D7247 Standard Test Method for Evaluating the Shear Strength of Adhesive Bonds in Laminated Wood Products at Elevated Temperatures ASTM D7374 Standard Practice for Evaluating Elevated Temperature Performance of Adhesives Used in End-Jointed Lumber
Bolts
Bolts are widely used in wood construction. They are able to resist moderately heavy loads with relatively few connectors. Bolts may be used in wood-to-wood, wood-to-steel and wood-to-concrete connection types. Some typical structural applications for bolts include: purlin to beam connections beam to column connections column to base connections truss connections timber arches post and beam construction pole-frame construction timber bridges marine structures Several types of bolts as shown in Figure 5.10 below, are used for wood construction with the hexagon head type being the most common. Countersunk heads are used where a flush surface is desired. Carriage bolts can be tightened by turning the nut without holding the bolt since the shoulders under the head grip the wood. Bolts are commonly available in imperial diameters of 1/4, 1/2, 5/8, 3/4, 7/8 and 1 inch. Bolts are installed in holes drilled slightly (1 to 2 mm) larger than the bolt diameter to prevent any splitting and stress development that could be caused by installation or subsequent wood shrinkage. Depending on the diameter, bolts are available in lengths from 75 mm (3″) up to 400 mm (16″) with other lengths available on special order. Bolts can be dipped or plated, at an additional cost, to provide resistance to corrosion. In exposed conditions and high moisture environments, corrosion should be resisted by using hot dip galvanized or stainless steel bolts, washers and nuts. Washers are commonly used with bolts to keep the bolt head or nut from crushing the wood member when tightening is taking place. Washers are not required with a steel side plate, as the bolt head or nut bears directly on the steel. Common types of washers are shown in Figure 5.11 below. Design information provided in CWC’s Wood Design Manual is based on bolts conforming to the requirements of ASTM A307 Standard Specification for Carbon Steel Bolts, Studs, and Threaded Rod 60 000 PSI Tensile Strength or Grade 2 bolts and dowels as specified under SAE J429 Mechanical and Material Requirements for Externally Threaded Fasteners. Download Figure 5.10 (and 5.11) as a PDF.
