Answers to common questions about engineered wood panels

By Merritt Kline APA Product Support Specialist

lr-THANCES ARE, if you're involved with engineered \-t wood, you've had an occasion to call the manufacturer about some aspect of installation or design. As more designers specify, more builders use and more dealers stock engineered wood products, more questions arise, from proper installation details to selectingthe right product for the right application.

At the APA Product Support Help Center in Tacoma, Wa., specialists handle hundreds of inquiries a week from dealers, builders, framers and designers who are using or planning to use engineered wood products. Here are some of the most frequently-asked questions:

Q wrrl.r, is stronger, plywood or OSB?

A

A The two products are virtually interchangeable. That's because both products, although different in composition and appearance, are manufactured according to the same performance standards. These standards apply the same performance criteria to both products for their designated snd uss5-sheathing, single-layer i"?Hil?""1*#:'#l'"'*l';ff ii,l- #w* | wood and OSB are qualified were developed to ensure reliable performance in service, to address a changing wood fiber supply, and to remove obstacles to innovative manufacturins technology.

Q f the gradestamp reads ',Sized For Spacing" must the panels still be spaced l/8" at panel edges?

A y"r. Since wood is a biological material and can expand when it absorbs moisture, panels should be spaced at ends and edges. The "Sized For Spacing" notification is intended to facilitate proper installation and specifies that the panels may be cut less than nominal dimensions from the mill to account for any expansion that may occur. The size tolerance of a 4'x8' "Sized For Spacing" panel, therefbre, may be 1/8" less than the specified length and width, e.g.,47-718"x95-7/8". However, since the size tolerance given in the performance standard allows up to l/8" less than the specified length and width, a 471/8"x 95-7/8" panel may or may not be stamped "Sized For Spacing."

How do I know if a particular panel meets the live and dead load requirements? A

A

The fastest way to determine live and dead load capacities is to check the APA load soan tables for roof and floor applications in the APA Residential and Commercial Design Guide. The tables provide allowable live loads for F panels installed over common support : (oist. truss or rafter) spacing configurations. The guide is available from our publications department or online at www.apawood.org.

Q no", structural panet siding have shear values?

Plywood (all-veneer) APA Rated Siding is often used for shear wall sheathing. The thickness of the panel at the point of nailing on the panel edges governs shear values. Other APA Rated Siding panel types may also qualify for shear values on a proprietary basis. To check for specific shear values, refer to the APA Residential and Commercial Design Guide.

Q Wf,", is the difference between Exposure I and Exterior panels?

A npn ftademarked panels may be produced in four exposure durability classifications: Exterior, Exposure l, Exposure 2, and Interior. 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 exposure to the weather or to moisture for its entire service life. Exposure I panels have a fully waterproof bond and are designed for applications where construction delays may be expected prior to providing protection.

Exposure I panels are made with the same exterior adhesives used in Exterior panels. However, because other compositional factors may affect bond performance, only Exterior panels should be used for permanent exposure to the weather.

Exposure I panels may also be used when exposure to the outdoors is on the underside only, such as roof overhangs.

How long can structural wood panels be exposed to the weather?

A t"." are many factors that affect the durability of wood structural panels, and each situation is unique. Although subjective, one way to determine if floor panels are suitable for use after a period of exposure is to walk on them. If they feel solid compared to your previous experiences with similar panels, spans and supports, they are "OK." After exposure to weather, 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 betweenjoists, 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. 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.

Q 1". the specification and use recommendations developed by APA applicable to products certified by other agencies?

No.

ASince the APA trademark appears only on products manufactured by member mills of APA, it signifies that the products are subject to the association's audit-arguably the toughest and most comprehensive quality auditing program in the industry. The technical information and product use recommendations developed by APA are based on research and testing of APA trademarked products only and therefore does not apply to panels certified by other agencies.

Q Wrr"t should be used when the architect specifies underlayment? A A Several panel grades and lay-ups are suitable for use as underlayment, however, the appropriate choice depends upon the type of finish flooring. For example, only fullysanded, veneer-faced underlayment panels meet APA recommendations for applications under resilient floor coveiings such as tile or sheet flooring or fully-adhered carpet.

One way to determine if floor panels are suitable for use after a period of exposure is to walk on them,

Other underlayment grades meet APA recommendations for less demanding floor covering applications such as carpet and pad and ceramic tile. To be assured that the right underlayment is used, check the APA Underlayment Guide at www.apawood.org.

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properly treated wood may soon be used across the country.