How the OSB is nailed to the wood frame structure determines how well the OSB actually does its job. There is no data to indicate that OSB bears any particular responsibility for moisture failures. When OSB does get wet it also tends to swell along the edges, and those edges stay swollen even after the material has dried out. The first piece of wood is placed so that it rolls “up” while each subsequent layer is laid 90 degrees to the one below it, and upside-down. Manufacturers also recommend a 2mm (1/8") gap be left between panels during installation to accommodate expansion. Part of the problem, of course, is the perrenial confusion between correlation and causality. Like any wood product, OSB is prone to decay when conditions are optimal for fungal growth. Vertical or sloped sheets will commonly fare better than horizontal panels in the same environment. The panel edges are especially vulnerable and therefore manufacturers protect the edges with paint or a special sealer. The OSB will need to dry out thoroughly if it remains. Careful decisions in design, construction and maintenance will prevent building leaks and other errors from causing water to go where it's not intended. OSB's other moisture challenge has to do with dimensional stability - in other words, OSB can irreversibly swell, especially at the edges, when it gets too wet. We've seen no damage to the roof structures, but the ridging is unsightly when the roofs are covered with asphalt shingles. However, it … Oriented Strand Board (OSB) that is conditioned for structural applications in humid environments. Curves Well – plywood curves much better than OSB does. This means OSB may degrade marginally more rapidly than other wood products, however the difference is probably not noticeable in practice. Swollen edges of osb panels can telegraph through thin coverings like asphalt roof shingles. This swelling is irreversible. This can be a real headache when one intends to install windows or doors with pre-manufactured liners. The term ghost lines or roof ridging was coined to describe the effect of osb edge swelling under thin roof shingles. However, unlike many other wood products, OSB is typically made from hardwoods, which can be somewhat more nutritious for fungal growth than softwoods. The moisture may also collect on the underside of the impermeable asphalt roof felt and shingles, compounding the problem. Like most other wood products, OSB is designed for use under dry service conditions. The swelling is minor unless the seams and edges will affect the horizontal plane of the siding. The laboratory OSB panels were fabricated as a multiple This is true no matter what the choice of construction materials. When marginal moisture conditions are anticipated, the addition of low levels of low-toxicity fungicides can be used to upgrade the durability of OSB. OSB that does get wet will tend to swell and delaminate first at the edges of the boards. Inject foam-in-place urethane into the seams before assembly or drill holes and fill the seams after the panels have been installed. Conventional OSB is suitable for all dry sheathing applications and treated, stabilised OSB should be used where moisture tolerance may be required. Inspecting the nailing pattern of the OSB is one of the fundamental inspections many building officials make. Internal Bond (IB) The IB strength of the OSBs ranged from 0.16 N/mm 2 to 0.34 N/mm 2 (Figure 2). Effects of Fines Content on the Internal Bond Strength and Thickness Swelling of Five-Layered OSB. As the indoor air cools, … Edge Gold includes patented Down Pore ® grooves that help shed standing water and a proprietary edge seal to reduce edge swell. Oriented Strand Board Cons; OSB is water resistant, but its sides and edges do tend to absorb water if they come in contact with it long term, so the bottoms and edges of the sheathing installation can wick up water, causing it to swell and warp. If a field cut of a panel slices away a sealed edge, take extra care to protect this now vulnerable side during construction. Oriented strand board (OSB) gets blamed for a lot of problems that are really the fault of the designers and builders. OSB takes longer to get wet than plywood but also takes longer to dry out. In addition, OSB is bonded with waterproof adhesives. OSB is strong and water-resistant. The same can't be said for OSB panels. OSB's other moisture challenge has to do with dimensional stability - in other words, OSB can irreversibly swell, especially at the edges, when it gets too wet. Copyright © 2021 Hanley Wood Media, Inc. Thickness swell was an important property of OSB for using in construction and outdoor facilities. In other words, as the percentage of buildings with OSB rises, and the proportion of leaky buildings rises, so does the chance of finding OSB when a house leaks. The necessary heat of reaction is wicked away by the cold, which can interfere with the curing process and leave an unprotected seam. This means the OSB - and all other components of the framing - should be kept dry through the life of the wall. When OSB gets wet, the strands of wood swell and they release some of the compression stress. The purpose of this study was to investigate the effects of resin and wax ratio on OSB properties and rapidly predict OSB properties using near infrared spectroscopy. It is important to note that OSB is not extremely sensitive to small amounts of water, and it absorbs water slowly. The solution is to meticulously seal the seams of adjoining panels with a product like spray urethane. So far, we haven't been able to find a solution, other than to make sure that the roofer covers the roof immediately with felt and uses good-quality shingle. moisture damages and problems for buildings, OSB- hygrothermal properties as compared to other sheathing panels, OSB - A research project in exterior sheathing. Swollen edges have been known to telegraph visible ridges called “ghost lines” through asphalt roof shingles. This is not a decay issue, but swelling can cause other difficulties in construction. It is often used in curved projects like eyebrow windows. Three-layered OSB (control) had relatively higher IB than does five-layered smooth surface OSB. It swells faster around the perimeter of the panel than the center. Oriented strandboard (OSB) has gained increased market acceptance as a construction material in almost all geographical areas of Canada and United States. It's the leak that's the problem, not the choice of product - a leaky building of any construction will quickly experience damage. OSB sheathing, which is always installed behind a moisture barrier, should not be confused with early makes of inadequately-protected wood composite siding, which performed poorly outside the moisture barrier. Make the Most of It. APA undertook a study to evaluate the relative thickness swell (RTS) of structural panels across interim moisture conditions from the oven-dried condition to complete saturation. Painting Difficult: Paint does not take well to OSB. We build timber frame homes and wrap them with insulated panels made with skins of OSB on the outhouse and rigid foam insulation on the inside. This is an unfortunate association arising from OSB's success at gaining market share at a time when the proportion of leaky buildings has been increasing as a result of other changes in construction practice. Some newer types of OSB, so-called "New-generation" OSB panels, use isocyanate resins that reduce the swelling risk.Isocyanate-resin panels do not contain formaldehyde and are considered … Plywood is made by cutting thin layers of a tree all the way around its circumference. Improper nailing. OSB exposed during construction must be allowed to dry (especially before installing sensitive finish materials such as hardwood flooring). What can happen with roof panels is that warm, moist air from inside the house leaks through the seams. Here's a sample question: What's the maximum span of an unsupported 2x12 stair... Business Lessons Learned - Solid PVC and Composite Sidings - Decks Over Roofs, JLC Online: Best practices for professional builders and remodelers, JLC Rolls Out Deck and Railing Skills Workbook, The Last Word (We Hope) on Vapor Barriers, Share of New Homes with Decks Declines Once Again, Adding a Quakeproof Deck to a Stucco Home, A Preview of the Virtual 2020 PSP/Deck Expo. A higher level of dimensional stability can also be designed into the product if these conditions are anticipated. Schedule delivery as close as possible to time of use and close in the structure from the weather as quickly as practical. It doesn’t swell much when exposed to water and is permeable, so it allows water to pass through without absorbing it. swell and so on. This is not to say that OSB has no problem whatsoever when exposed to excessive moisture. The block hardens into a sheet that can be used for building shelving or furniture. What does OSB 3 mean? The biggest knock leveled at osb is its tendency to swell around the panel edges. Swelling of the OSB panel is the ultimate contributor to the loss of structural strength. Moisture: OSB, when exposed to the weather, will eventually swell and bubble up. Without the 1″ of foam (your 3/8″ may not be adequate), the OSB stays cold and when the interior moisture drives through the wall from the interior, it gets colder as it approaches the OSB. Do not allow panels to sit in pools of water. Be careful about using spray-in-place urethane to seal panels in cold weather. Figure 12. When used as a roof sheathing, this tendency to hold moisture means it can degrade faster than plywood when exposed to chronic leaks. Ground exposure, however, will accelerate deterioration and rot too. Edge™ ™and Edge Gold Specifier’s Guide OSB-4000 | April 2014 2 Edge™ oriented strand board (OSB) floor panels help builders get an edge on their competition by delivering both the value and product reliability needed for solid, stable floors. When OSB does get wet it also tends to swell along the edges, and those edges stay swollen even after the material has dried out. OSB manufacturers have been working hard to reduce this problem. This is due to two main concerns: A change in the panel thickness will occur while the fastener does not move, resulting in a fastener that is no longer flush to the face of the panel but is essentially overdriven. Check with the spray-foam manufacturer for recommendations on cold weather installations. Easily recognized by their green edge seal, each Edge™ panel is uniform in size to allow easy installation, minimal waste, and Plywood can and does swell, but typically once it dries, it returns to its original size and shape. OSB that does get wet will tend to swell and delaminate first at the edges of the boards. In general, though, OSB is less expensive. OSB takes longer to get wet than plywood but also takes longer to dry out. The trade term OSB/3 comes from the technical class denoted in BS EN 300 for ‘load-bearing boards for use in humid conditions’. Our Life and Work are Now on Zoom. We've been pleased with the results except for one thing: the swelling of the OSB at the edges. The result is that the tendency for the boards to warp into their original shape is diminis… Keywords: OSB, internal bond, thickness swell, MOR, MOE. This sealer is usually coloured. It happens to get cold enough to condense inside the OSB which causes it to swell. Installing dry is virtually impossible in rainy climates, however, brief periods of wetting should not cause decay problems, provided OSB dries below 16% before the air barrier and cladding are both added. Store panels indoors or under cover, with enough support to keep panels flat. Panels should be protected from excessive wetting during storage and construction. Another reason it is used in subfloors. This is similar to the method used to manufacture oriented strand board and plywood. Swelling can be leveled with a belt sander. The panel edges take on moisture more quickly than the rest of the panel and swell as a result -- one of the shortcomings of OSB. A: Contributing editor Paul Fisette responds: This problem, caused by moisture adsorption, has been reported before with stressed-skin panels installed on roofs. When used as a roof sheathing, this tendency to hold moisture means it can degrade faster than plywood when exposed to chronic leaks. Nonetheless, it can be painted. Once the building is closed in, the ability of the wall to dry is dramatically reduced. Please see "Proper Handling" below for tips on preventing swelling. There are some applications where OSB is not advised by manufacturers. Aligning Cabinets With Plumbing Rough-ins, Slip Sliding Away: Upcoming Webinar Focuses on Slippage, Transcendent Investment Management and Electra America Form Joint Single-Family Rental Venture, Case-Shiller Home Price Index Reports 10.4% Annual Gain To End 2020, Sunnova Acquires Lennarâs SunStreet Residential Solar Platform, Tri Pointe Homes CEO Doug Bauer on Industry Trends and Brand Consolidation, The Challenges Millennials Face to Attaining Homeownership. Most panels are also treated with a sealant on the panel edges to retard moisture penetration. Overdriven staples due to thickness swell after panels have been wetted and overdriven fas-tener performance under lateral loads for OSB wall panels in accordance with PS 2-04, Performance Standard for Wood-Based Structural-Use Panels Figure 13. OSB is manufactured dry and should be transported, stored and, ideally, installed dry. If the OSB is covered with foam sheathing it is pretty tough to do … OSB typically runs half the price of the same thickness of plywood. We occasionally hear the suggestion that OSB is especially prone to decay and is associated with the moisture failures that increasingly plague homeowners across North America. When OSB does get wet it also tends to swell along the edges, and those edges stay swollen even after the material has dried out. The mold will have to be dealt with using bleach or comparable. The panel edges take on moisture more quickly than the rest of the panel and swell as a result -- one of the shortcomings of OSB. In such cases, the exact thickness of the walls can complicate final finishing work. If handled properly, OSB can accommodate exposure to some water without swelling. For equivalent fungal resistance to Douglas-fir-faced plywood, Forintek recommends a combination of 0.2% zinc borate added during manufacture and 10 mg/cm2 Oxine copper sprayed on the surface. Uncut OSB will also outlast cut pieces. Preservative-treated OSB and wood composite siding are now available in the marketplace. These boards are then laminated together using a hot press (basically a giant iron that fuses wood and glue together under heat). Caulk any gaps. Minor instances of bubbling can be sanded, but for the most part, the OSB is irreparable and should be replaced. However, it is also slow to dry out. OSB does not hold up to moisture as well as plywood, but it is better than partical board - with that said though, there is an OSB product that DOES hold up pretty well - its called AdvanTech Sub Floor, sold at Lowe's - This is an extremely durable OSB product. It is important to note that OSB is not extremely sensitive to small amounts of water, and it absorbs water slowly. OSB has a tendency to swell on the edges when exposed to water, but it resists humidity well compared to plywood [source: University of Massachusetts ]. For applications where the moisture content remains above 28% for extended periods, such as siding, higher levels of preservative (0.75% zinc borate) are added to OSB during the manufacturing process. Unprotected or untreated OSB panels exposed to the elements will weather and gray, swell, and even delaminate over time. Zinc borate additionally provides termite resistance. However, it is also slow to dry out. It has some inherent moisture resistance, due to the resins which hold together the strands, along with some wax which is added to the product specifically for this purpose. The thickness swell of OSB is generally greater than wood due to release of compaction stress created during pressing. Paul Fisette is a wood technologist and former director of the Building Materials Technology and Management program at the University of Massachussets in Amherst, Mass. OSB hit the market as we really started getting serious about insulation and air sealing. OSB panels are created under enormous pressure as the wood strands and resins are compacted. OSB's other moisture challenge has to do with dimensional stability - in other words, OSB can irreversibly swell, especially at the edges, when it gets too wet. Swollen plywood will return to its nominal thickness as the wood dries, while OSB will remain permanently swollen, to some degree. What can happen with roof panels is that warm, moist air from inside the house leaks through the seams. OSB's other moisture challenge has to do with dimensional stability - in other words, OSB can irreversibly swell, especially at the edges, when it gets too wet. Interestingly, in above-ground field tests of small boards, OSB fully exposed to drying on both sides remains free from decay for many years. Please see … Swell is generally greater in OSB than in plywood due to the release of compaction stress in OSB created during the pressing of wood chips into panels. 4. Can you waterproof OSB? This is not a decay issue, but swelling can cause other difficulties in construction. As the indoor air cools, the moisture condenses and wets the panel edges. Occasionally, oriented strand board (OSB) panels may exhibit thickness swell after being exposed to jobsite moisture/water during project construction. This can be avoided with sealants, but it is an extra step that needs to be considered. The severity of the condition generally depends on the amount of water and the length of exposure. It is important to note that OSB is not extremely sensitive to small amounts of water, and it absorbs water slowly. Once osb swells, it stays swollen and expanded panel edges can telegraph through thin roof finishes like asphalt roof shingles. There's no set price for OSB and plywood, so it's difficult to compare prices. OSB is not recommended for use where it would be in sustained contact with a moisture source, such as soil or concrete within 150mm of soil level. Have you seen any instance where this swelling has contributed to roof failure? OSB's other moisture challenge has to do with dimensional stability - in other words, OSB can irreversibly swell, especially at the edges, when it gets too wet. After OSB is nailed to rafters or trusses on a roof (or, as in your case, to the existing solid wood sheathing), it can swell as it picks up moisture from the air and from the attic below. The mixture is formed into blocks and baked for a long time at high temperatures and pressures.
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