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LEAKY BUILDINGS AND DECAYING WOOD – WHAT’S HAPPENING? The news across North America seems to frequently contain stories about serious moisture failures in wood-frame buildings. Whether it’s Vancouver’s “leaky condo crisis” or the “EIFS disaster” in North Carolina, homeowners are struggling with wood decay wherever the other components of the building’s walls and roof aren’t properly protecting the wood structure from excessive moisture. Interestingly, leaks are also getting attention in steel and concrete high-rises, causing rust in steel studs and fasteners and degradation of gypsum wallboard. Why are we suddenly finding so many failures in buildings, including in our tried-and-true wood construction? This is a frustrating problem for everyone in the building industry, because there are no easy answers. It’s convenient to blame unskilled or unethical practitioners in the building industry. Other occasional targets for blame include municipalities for developing zoning ordinances that conflict with performance issues; energy efficiency codes for making our building envelopes tighter; new and complicated materials in our building envelopes; the building occupants for not practising proper maintenance; or the wood, which some seem to feel has declined in quality. The bottom line: many people have opinions, but so far there is little firm technical data to answer these questions. Please see our Links page for some of the research institutions working in this area. Buildings have probably always leaked, although it is only recently that moisture seems to be a problem. Some believe that the difference is that today’s buildings are less tolerant of those leaks; that perhaps the older buildings were able to dry out. Another theory is that today’s leaky buildings leak more than in the past, due to design errors, sloppy construction, lack of overhangs, etc. Thankfully, many people working in the building industry have turned their attention towards better design and construction practice for moisture control. A number of “best practice guides” are listed in our Links section. HOW CAN I TELL IF WOOD IS DECAYED? If wood is badly decayed, this will be quite obvious. The wood will be soft and perhaps even be breakable by hand. Decayed wood breaks with a carrot-like snap versus the splintering of sound wood. Use the pick test to be sure. MY WOOD IS STAINED – IS IT DECAY? Probably not, if this is new lumber. There are many harmless sources of wood stains, including dirt, iron filings, or staining fungi that merely colour the wood without damaging it. Please see the fact sheet “Discolourations on wood products: Causes and Implications” for a thorough explanation including photos. If the discoloured wood is found in a leaky building under repair and may have been wet, perform the pick test to see if it is rotted – see our page on Assessing decay. I HAVE DECAYED WOOD – WHAT SHOULD I DO? Remove all decayed wood and additionally remove another two feet of sound wood all around the decayed section. Any sound wood that is left in place when decayed wood around it has been removed should be field treated with a penetrating preservative. Also field treat any wood that may continue to get wet after repairs. We recommend preservatives containing a diffusible low-toxicity fungicide such as sodium borate, and low-toxicity formulating agents which assist in penetrating dry wood, such as propylene glycol. By the time the cladding has been removed, the structure has been inspected and the decayed wood has been removed, the wood left in place will likely have dried too much for effective use of formulations without a penetration aid. Under conditions of high relative humidity, the propylene glycol may cause a short term increase in the moisture content at the wood surface. For more information, please see our page on Assessing decay. IS KILN-DRIED LUMBER MORE RESISTANT TO DECAY THAN GREEN OR AIR-DRIED LUMBER? One advantage of kiln-dried lumber is that any live fungi present in the green lumber will have been killed by the heat of the kiln; in other words, KD lumber is sterile after leaving the kiln. However, if it gets sufficiently wet afterwards, then it is at the same risk of decay as any other wood. ARE COMPOSITE WOOD PRODUCTS MORE RESISTANT TO DECAY THAN SOLID LUMBER? No. Composite products (glulam, OSB, laminated veneer lumber, etc.) have the same resistance to decay as the wood from which they were made. The adhesives used in composites do not affect decay resistance. DO WE HAVE TERMITES IN CANADA? Yes, in a few limited areas across the country and to a greater extent around Toronto, termite species causing damage to buildings are present. Although termites are a significant problem in parts of southern Ontario, overall they are only a mild concern in this country. They prefer warmer conditions and are a far greater problem in parts of the United States. In Canada we do not have the voracious Formosan subterranean termite causing so much damage in the southeastern US. WHAT IS DRY ROT? Contrary to popular usage, dry rot does not mean rot that can happen in dry wood, or wood that has rotted and dried out. Dry rot is a specific kind of fungus, although the term is very commonly misused to describe all wood rot. This is unfortunate, because it disassociates rot from moisture. Wood rot always requires moisture, and the key to wood durability is the control of moisture. Wood that rotted long ago and is now dry was moist at the time of the rot. The true dry rot fungus has the ability to tap into a water source and conduct water to what would otherwise be dry wood. However, it has to wet the wood before it can attack the wood. The true dry rot fungus is more likely to be found in buildings that contain brick or stone than in all-wood buildings. HOW FAST DOES WOOD DECAY? It’s impossible to say; there are so many variables that influence the process. In a laboratory, under ideal conditions for decay fungi, wood can rot quite quickly.

Sometimes it happens – wood in service suffers from decay. How can you identify decayed wood and what are the recommended actions to take? First, be sure you actually have decay. The wood may only be harmlessly discoloured, for any number of reasons. See the publication in the side bar for help if your wood is stained but you’re not sure why. If wood is badly decayed, this will be quite obvious. The wood will be softer than normal and perhaps even be breakable by hand. Decayed wood often has a colour change, either darker or lighter than normal, although this could be due to weathering or could just be a stain. The wood may display an unexpected cracking pattern, or may look stringy- this is a sign of fairly advanced decay. If fungal growth is visible on the surface, the wood has quite likely already suffered strength loss even if this isn’t visibly obvious. However, do not rely on visual cues alone. Wood can appear stained and yet be sound, or can appear normal yet have already suffered significant strength loss due to decay. Some researchers or engineers use the pick test to determine if the wood is sound. They insert the point of a knife at a shallow angle to the surface and attempt to lever up a thin splinter. If the wood splinters with longer fragments, it is likely sound. If instead it breaks or crumbles in small pieces over the blade, it could be decayed. Decayed wood breaks somewhat like a carrot snapping in half, at one section, versus the splintering along the length of sound wood. See our Biodeterioration page to learn more about the science of decay. If you are still unsure whether or not you have decayed wood, you are advised to seek help from a wood restoration specialist. How urgent is a decay problem? By the time you notice decay, the wood typically has lost substantial strength already. In cases where the decayed wood is supporting load you are strongly advised to contact a structural engineer or other appropriate expert to more thoroughly assess the problem and proceed with a repair. A small, localized and non-critical case of decay may be a do-it-yourself project under some conditions. All decayed wood should be removed. If you are unable to remove the entire affected piece, remove the decayed portion plus an additional portion of adjacent wood beyond the visible decay. A rule of thumb is to remove an additional two feet (60 cm) of adjacent wood from each side, although this will of course depend on the extent of the decay. The removal of adjacent wood is because the fungus may have extended deep into the wood beyond the area of decay and may be ready to cause more damage in adjacent sound wood. Then apply a field treatment to the remaining adjacent wood, such as a borate solution in roll-on, rod or paste form, before replacing the removed pieces. Use treated or naturally durable wood to replace the removed pieces. If damaged wood must be left in place, a penetrating epoxy can sometimes be applied as a stabilizer. In those cases and for best results in all wood repair projects we recommend you consult with a wood restoration expert. Indoors, it is extremely important that you find the source(s) of the moisture that allowed wood decay fungi to grow. If you had wood decay in a location that is supposed to be dry, then you have a leak or a condensation problem that needs fixing to prevent any future problems. Look for primary and secondary sources of moisture. A short term leak may have allowed decay to start, for example, and condensation may be sustaining the decay. If the location of the decayed wood was outdoors or in a wet location, you need to use treated or naturally durable wood. If you have building moisture problems on a large scale, you need to hire some experts and be prepared for a potentially substantial remediation project. Seek out a qualified consultant, who will begin by using a variety of techniques and tools to determine the extent of the damage. This will include a visual examination for staining, bulging, cracking, presence of water, and warping. Subsurface moisture penetration will be tested with probes and/or thermography. In a building with wood structural members, the consultant will probably use a moisture meter to sample wetness of structural wood components in several locations. Based on the results of this investigation, the consultant will recommend a course of action for repair and future prevention. Canada Mortgage and Housing Corporation has developed a guide for building envelope rehabilitation, in two volumes: one for owners, one for consultants. More Information Click Here for a fact sheet Discolourations on wood products: Causes and Implications for help if your wood is stained and you’re not sure why. Click here for more information on biodeterioration and the science of decay. Click here for more information on remedial treatments. Click here for links on decay assessment and other durability topics

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

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.

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  

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.

Wood, a long-lasting, economical, and renewable resource, is the building material of choice in North American housing. This is largely due to the proven performance of properly designed and built wood frame buildings that have provided strong and lasting housing for a multitude of people. Although wood can withstand much abuse, it needs to be stored and handled properly to perform according to expectations. Managing moisture in structural wood products is essential in order to control swelling and shrinkage and prevent problems associated with mold or decay.

Wood products have long been the building materials of choice for home construction in North America. The wood-frame construction system has a solid history of producing housing of the highest standards: It is easy to build, delivers economic value, has excellent strength in earthquake or high-wind conditions, is energy efficient, and is derived from a renewable resource. Modern wood-frame construction includes several types of engineered wood products that are economically viable in multi-story residential buildings and non-residential projects. Moreover, as described in Bulletins No. 1 and 2 in the Building Performance Series, wood framing supplies durability and fire safety performance where environmental and building code requirements are met. This bulletin describes how wood framing can also be used in areas of North America subject to insect attack, a threat to all types of buildings. It builds on the concept of integrated pest management that will provide long-term protection for wood-frame and other buildings against damage caused by insects, specifically Formosan and other subterranean termites. Also included is practical advice for building designers, contractors and owners to assist in assessing risk, and choosing appropriate mitigation measures.

Throughout history, wherever wood has been available as a resource, it has found favor as a building material for its strength, economy, workability and beauty, and its ability to last has been demonstrated again and again. From the ancient temples of Japan and the great stave churches of Norway to the countless North American buildings built in the 1800s, wood construction has proven it can stand the test of time. The art and technology of wood building, however, has been changing through time. Can modern wood-frame buildings perform as well? Protection of buildings from moisture is an important design criterion, as important as protection from fire or structural collapse. Designers, builders and owners are gaining a deeper appreciation for the function of the building envelope (exterior walls and roof). This includes the performance of windows, doors, siding, sheathing membranes, air and vapour barriers, sheathing, and framing. The capabilities and characteristics of wood and other construction materials must be understood, and then articulated in the design of buildings, if proper and durable construction is to be assured. This guide will help design and construction professionals, and building owners understand moisture issues related to the design and construction of wood-frame buildings. The primary objective is to provide ideas and solutions to ensure wood-frame buildings perform as expected. The primary focus of the guide will be on the control of rainwater penetration in exterior walls, particularly for climates subject to high moisture exposure.

Throughout history, wherever wood has been available as a resource, it has found favor as a building material for its strength, economy, workability and beauty, and its ability to last has been demonstrated again and again. From the ancient temples of Japan and China and the great stave churches of Norway to the countless North American and European buildings built in the 1800s, wood construction has proven it can stand the test of time. The art and technology of wood building, however, has been changing through time. It’s a common misconception that water is wood’s enemy. That’s not necessarily true, since many wood buildings exist in rainy and humid places. It’s a matter of knowing how to manage water in buildings. Protection of buildings from water is the important design criterion, as important as protection from fire or structural collapse. Designers, builders and owners are gaining a deeper appreciation for the function of the building envelope (exterior walls and roof). This includes the performance of windows, doors, siding, sheathing membranes, air and vapour barriers, sheathing, and framing. The capabilities and characteristics of wood and other construction materials must be understood, and then articulated in the design of buildings, if proper and durable construction is to be assured. Wood and water are typically very compatible. Wood can absorb and release large quantities of moisture without problems, and it’s only when wood gets too wet for too long that there may be problems. If buildings are properly constructed to shed water, wood performs well as a building material in all types of climates. As an example, 90% of North American homes are built with wood. The primary focus of this publication is to address the control of rainwater penetration in exterior walls, which is the major source of moisture issues for all building materials, particularly in climates subject to high rainfall.