Panel products such as plywood or OSB (OrientedStrand Board) are at a - PDF document

Panel products such as plywood or OSB (OrientedStrand Board) are at a low moisture content at the time of manufacturing (see Table 1).Engineered wood products such as I-joists alsotend to have moisture content lower than S-Drylumber, which keeps them very dimensionally stable as long as they are dry.Table 1: Typical Moisture Content of Wood Products at Time of Manufacture ProductMoisture Content Lumber Ð S-Dry19% or less Lumber Ð S-GreenUsually over 19% Panel products (OSB, plywood)4-8% I-Joists4-16%Wood that is Not Kept DryWood that is in contact with water over a longperiod of time can become discolored for variousreasons and may grow fungi, including stains,molds and decay. If wood stays wet, it can take on a darker appear-ance due to the water. This dark appearance willdisappear when the wood dries again, but if it stayswet too long, it may become permanently discolored.Discoloration of the wood may be due to moistureissues or other causes.Potential causes of discoloration in wood include:¥Staining fungi (usually ÒbluestainÓ that goes deep into the wood) ¥Weathering (gives wood a grey colour)¥Decay fungi (the wood may be weaker)¥Mold (may appear in various colours - grey, red, brown, black, white yellow)¥Dirt (will rub off when dry)¥Iron stain (caused by steel straps, machinery fromtransportation or manufacturing)¥Yeasts (black and slimy to the touch)¥Miscellaneous chemical stains (caused by Of these, only decay will affect the structural per-formance of the wood; other forms of discolorationwill not weaken the wood. In the case of stainingfungi, the staining may have occurred in the treebefore the wood was sawn into lumber, althoughstoring wet lumber over a long period of time mayalso cause staining of the wood.Decay fungi are different from molds and stainingfungi. Molds and stains feed off the free water andthe sugars stored inside the wood but donÕt affect the wood strength. On the other hand, decay fungiwill gradually eat the wood if it remains wet for tooare also favorable to decay, the presence of mold or stain does not indicate that there is decay. Still,excess water, as well as moderate to warm tempera-tures that sustain mold growth, could ultimately lead to decay, if the wood is not quickly dried. 4 Figure 3: Potential Sources of Moisture potential to thrive where there is moisture. Theyhave received much public attention after havingbeen identified as a contributor to poor indoor airquality, along with dust, mites and other factors.Molds can grow on many surfaces, including wall-unknown factors regarding molds and their effectson health, one thing is for sure: molds indicate aproblem with moisture management in the building.Water can come from various sources and the way to solve the problem is to remove these sources.is a good practice to reduce the chances of problemsPotential causes of water entry in the building include:¥Plumbing failure¥Poor thermal performance¥Poor detailing of the envelope (leaks)¥Poor ventilationWall construction practices have evolved. Air tightness is emphasized and many new materials are available for wall construction. Though there aretypically provisions included in the wall design forthe building envelope to dry, it is good practice toensure that building materials are dry (ie. 19% MCor less) at the time of enclosing the wall. Refer to theMost building codes require that wood be dried to19% MC or less. This moisture content is sufficientlylow to virtually eliminate the chances of moldgrowth on wood products as well as minimizedimensional changes in the members.Wood used in BuildingsIn normal applications, wood will undergo changes inmoisture content throughout its life in relation to sea-sonal changes in relative humidity and temperature.For example, in more humid regions, wood will haveManaging Moisture and Wood Figure 4:Moisture Content vs. Humidity and the Risk of Mold Growth Safe ZoneIntermediate 2030405060708090100 Storage and Handling Techniques¥Ensure storage area is well-drained and clear of obstacles, debris, and vegetation(Vegetation can harbour insects, prevent good ventilation and keep the air moist).¥If the soil is wet or poorly drained, place a poly-ethylene tarp or a temporary gravel pad on theground below the supports for the materials.¥Keep packages of lumber, trusses, I-Joists andpanels 6 to 8 inches off the ground (dry wood in contact with the ground will quickly take ¥Store bundles as level as possible. DoDonÕtHave the material delivered as close to the Let the materials sit too long. Materials left exposed installation date as possiblerisk water absorption and deterioration, as well Protect the materials after they have been installed Hurry to Òclose-inÓ the walls, especially if the by closing the structure quickly (walls/roof)wood is green and/or has been wettedProvide enough time and ventilation for the materials before installing the vapour barrier, when elevated moisture levels have been detected Building Performance Series No. 6 8 Horizontal wood components, however, need more time to dry. Temporary protection Figure 8: Drying need of ConstructionVertical wood Managing Moisture and Wood Figure 10: Storage off-groundWrapping¥Keep wrappers on the bundles until they areready to be used.¥Re-cover using a waterproof tarp if the wrap-ping is damaged. WARNING: Tarps developholes easily on lumber corners or other points of stress.¥The tarp should not be tucked under the pileor wrapped tightly.¥Make sure the tarp covering extends beyond Beware of polyethylene tarps; though they areefficient at protecting the wood from soil mois-If Wood is Re-Wetteddegree of water repellence and are not easily wetted by a small amount of rain. Wood gets wet and dries from the outside in. In cases ofwetness, the wood will dry quickly on the surfaceWood products are most commonly stored insolid piles. With tidy piles of panel products, thetop panel can retain the moisture but most of the water runs off and does not readily penetrateinto the pile. Piled lumber can be more vulner-between the lumber pieces and may wet severallayers. Such water is held between the boards asa film that wets the surfaces. Wood in this situa-surface mold or wood-staining fungi. For longerterm storage, lumber should be stickered. Figure 9: Well protected bundles Canadian Wood Council99 Bank St., Suite 400Tel: 1-800-463-5091www.cwc.ca CanadianWoodConseilcanadien Remedial Procedures for Water Damage in BuildingsTedd Nathanson, Environmental Services, Public Works and Government Services Canada. 2002www.pwgsc.gc.ca/rps/aes/docs/pdf/iaq_pub_remedial-e.pdfNew York City Department of Health and Mental Hygiene. 2002www.ci.nyc.vs/html/doh/html/epi/moldrpt1.htmlWood Frame Envelopes Ð Best Practice Guide,Building Technology. Building Performance Series No. 6 Building Performance Series No. 6 Building Performance Series No. 6 Canadian Wood CouncilOttawa, ON K1P 6B9Tel: 1-800-463-5091 Canadian Wood CouncilTel: 1-800-463-5091 Remedial Procedures for Water Damage in BuildingsTedd Nathanson, Environmental Services, Public Works www.pwgsc.gc.ca/rps/aes/docs/pdf/iaq_pub_remedial-e.pdfNew York City Department of Health and Mental Hygiene. 2002www.ci.nyc.vs/html/doh/html/epi/moldrpt1.htmlWood Frame Envelopes Ð Best Practice Guide,Building Technology.