303 ROSE WAY 2018-01-02 MF Import

A P A The Engineered Wood Association This is in response to your request for guidance on evaluating APA trademarked wood structural panels exposed to weather for an extended period of time. Please keep in mind that this information applies only to APA trademarked products and may not be applicable to other products APA trademarkei panels are produced in two exposure durability classifications — Exterior and Exposure 1. The exposure durability classification relates to glue bond, and thus to structural integrity. Exterior panels have a fully waterproof bond and are designed for applications subject to permanent exposure to the weather or to moisture. Exposure 1 panels have a fully waterproof bond and are designed for applications where long construction delays may be expected prior to providing protection, or where high moisture conditions may be encountered in service. Exposure 1 panels are made with the same waterproof adhesives used in Exterior panels.) Exposure 1 panels may also be used when exposure to the outdoors is on the underside only, such as at roof overhangs. Although glue bond durability is described by exposure durability classification, the surface of a panel may become uneven and irregular under prolonged moisture exposure. This "weathering" of panels is an aesthetic consideration and is not detrimental to structural capacity. Swelling of panel edges and uneven swelling of individual wood strands may be expected on OSB sheathing panels exposed to high moisture conditions. This can cause a rough, uneven surface that may detract from the appearance of smooth panels. Inherent in the swelling, some lifting of wood strands may also occur. There are many factors that affect the durability of wood structural panels and each situation is unique. Although subjective, the best way to determine if panels are suitable for use after a period of exposure is to walk on them. If they feel solid compared to other experience with similar panels, spans and supports, they are "OK." It is a judgment call. It is not uncommon for panels to be exposed to weather for six months to a year. Such panels often look rough but remain structurally serviceable. After the building is "closed in" and protected from the weather, the floor should be allowed to dry to in-service moisture conditions. Before installing any finish flooring the floor deck should be inspected for flatness between joists, and also for smoothness along end and edge joints between panels. Any ridges or thickness swelling at these locations should be sanded smooth. Wall and vertical surfaces allow water to "shed" quickly. later, after the roof framing, sheathing and roofing are installed, roof overhangs (if provided) will further protect the sheathing from exposure, although the panels may get wet from exposure to rain especially on the lower parts of walls or if wind driven rain occurs. Before installing the exterior and interior finish, wall sheathing should be allowed to dry so that moisture absorbed during construction will not be trapped within the wall cavity. For roofs, APA recommends covering the sheathing as soon as possible after installation with roofing underlayment (asphalt impregnated felt per ASTM D226 or other product as recommended by the roofing manufacturer). This will allow the interior of the building to start the drying process. If this is not possible and the roof sheathing has been exposed for a period of time allow the roof sheathing to dry (from the underside) before closing in the roof cavity or attic. 7011 South 19th Street • P.O. Box 11700 • Tacoma, WA 98411.0700 Telephone (253) 565-6600 • Fax Number (253) 565-7265 Z1S