OSB Frequently Asked Questions

Because it is engineered, OSB can be custom manufactured to meet specific requirements in thickness, density, panel size, surface texture, strength, and rigidity. This engineering process makes OSB the most widely accepted and preferred structural panel among architects, specifiers and contractors.

This engineering process makes OSB the most widely accepted and preferred structural panel among architects, specifiers and contractors.

Logs are cut to length, debarked, and processed into precise strands ranging from 3 1/2" to 6" (90 to 150 mm) long and approximately 1" wide (25 mm).

The strands are dried, sorted, and mixed with wax and a waterproof exterior-type binder and formed into large continuous mats. These mats are oriented in cross directional layers for increased strength, then pressed at a high temperature and pressure to form panels.

Throughout this highly automated and fully engineered process, panels are monitored, tested, and certified to meet stringent quality standards for strength and uniformity.

• CSA 0325 and/or CSA 0347 (for Canada)

• PS2-04 (for the U.S.A)

• EN 300 and HEN13986 (for Europe)

• JAS for Structural Panels (Notification 360 and 1604, MAFF) (for Japan)

• TECO-PFS, APA or PSI/PTL Performance Standards (respectively NER-133, NER-PRP108 or NER-231).

This guarantee means that panels made by SBA members will perform as specified for the intended use when installed in accordance with the Installation Instructions published by the SBA member company.

The SBA Members' guarantee stipulates that should any panels not comply with the performance criteria specified in the standard(s), the SBA member will, at its option, either supply replacement panels without charge or reimburse the buyer for the full purchase price of the defective panels.

Terms of this guarantee can vary and should be confirmed with the respective companies. The SBA does not offer any specific product guarantees.

In addition, span ratings are stamped on each panel. (These ratings denote maximum recommended spacing of supports for load-bearing conditions.)

OSB also is Exposure 1 rated for durability, which means that it is designed to perform in applications where construction delays may occur. It requires no special treatment, only the same degree-of-care as other wood products. As with other structural wood panels, prolonged direct contact with rain or standing water should be avoided.

• Only trees from sustainable, fast-growing forests or woodlot thinnings are required in the manufacturing process, so there is always an abundant supply of convenient, high-quality raw materials.

• The panel is engineered for uniformity, eliminating costly surprises like core voids and knotholes, so you can use what you buy and get what you pay for.

• OSB is manufactured worldwide, meaning its abundant supply and easy access ensures economical purchasing and shipping methods.

• OSB is a better value than other structural panels.

• OSB also offers increased flexibility in selecting panel thicknesses and sizes.

• As the only truly renewable building material, wood is increasing its reserves every year.

• OSB uses selectively prepared new wood strands during its manufacturing process and is recyclable into other products.

• The fiber for OSB is grown in sustainable forests and tree farms.

• OSB is safe to use.

• Resin binders and waxes are completely cured and stabilized, so there is no measurable off-gassing from panels.

• The manufacturing process uses nearly 90% of the log, with the balance used to supply energy.

• It takes far more energy and resources to produce steel, concrete or other building materials than to manufacture a structural wood panel.

• Modern mills -- costing more than US$ 100 million -- are scientifically designed to meet or exceed strict standards for environmental compliance, set by regulatory authorities.

Typically, OSB is 95 to 97 percent wood, and 3 to 5 percent additives like wax and resin. The characteristics of a well-managed landfill will mitigate any adverse effects to health or the environment.

Other tests were conducted by Forintek Canada Corporation, a major independent Canadian research firm. The tests used OSB panels coated with latex interior paint and two fire-retardant paints, which improved their flame spread ratings.

The model building codes also recognize the equivalent performance of OSB and plywood panels in many wall or floor assemblies requiring a minimum fire rating.

Tests were conducted under both wet and dry climatic conditions using OSB panels from a variety of SBA-member mills.

The test was co-commissioned by the SBA, along with the Composite Panel Association in the United States, and Forintek Canada Corporation.

These findings support the blanket exemption given by HUD to manufacturers of phenol formaldehyde-bonded wood panel boards from the need to either test for formaldehyde emission or to attach consumer warning labels to the panels.

Tests on OSB panels have also been proven to meet the requirements of the European and Japanese emission criteria.

OSB compares favorably with other structural panels. Panels with a permeability of 1.0 perm (60 ng/Pa.s.m2) or less are considered to act as vapor barriers and panels with a permeability of 2.0 perms (12 ng/Pa.s.m2) or more are considered to pass sufficient water vapor that a wall cavity will dry out when constructed with green lumber.

For example, 5/8" (15.5mm) panels can be installed as a floor over unheated well ventilated spaces without the need of a vapor barrier, while 7/16" (11 mm), when installed as wall sheathing, will allow a wall cavity containing saturated stud lumber and glass fiber insulation to reach an equilibrium moisture content below 19 percent in approximately 60 days.

Sheathing membrane, although not always specifically mandated in some building codes under some types of claddings are recommended over OSB wall sheathing.

• 1/4" (6 mm)

• 3/8" (9.5 mm)

• 7/16" (11 mm)

• 15/32" (12 mm)

• 1/2" (12.5 mm)

• 19/32" (15 mm)

• 5/8" (15.5 mm)

• 23/32" 18 mm)

• 3/4" (18.5 mm)

Other thicknesses are available on special order. Panels 19/32" (15mm) and thicker are manufactured either square-edged or tongue and groove on the long edge.

OSB is certified to meet these standards by APA - the Engineered Wood Association, TECO (or PFS), PSI, or other major wood certification organizations. In addition, OSB is regulated in all model building code organizations - ICC, BOCA, ICBO, NBCC, CABO, and SBCCI. OSB is manufactured to meet the Exposure 1 durability classification, meaning panels are appropriate for use where construction delays may occur.

In Europe, OSB panels are manufactured to meet EN-300, Oriented Strand Boards and are certified by national certification agencies.

For Japan, OSB panels must meet JAS requirements and can be certified by recognized North American certification agencies.

Panels should be installed textured side up with their long direction across the rafters or truss chords. Long panel edges should be supported or joined with edge clips where specified by the drawings or installation instructions. Leave a 1/8" (3 mm) gap at panel edges or ends to allow for movement due to changes in humidity.

Panels should be staggered at least two supports, and end joints must lie over supports. Use 2 1/2" (63 mm) common (8d) or 2" (50 mm) deformed shank or ring thread nails at 6" (150 mm) o.c. on panel edges, at 12" (300 mm) o.c. along intermediate supports and 3/8" (10 mm) minimum from panel edge. Staples may be used instead of nails - please consult your local building code for size and spacing. Stand over the trusses or rafters when nailing.

The roof should be dry prior to shingling and should be shingled as soon as possible after installation of sheathing. It is essential that the area under a roof system is adequately vented with 50 percent of the venting at the ridge and 50 percent around the eaves. Vent roof as specified in the appropriate building code or as shown on the approved drawings.

Lay panels across three or more supports, keeping the side marked "This Side Down" on the supports when using T&G panels. End joints must be made over the supports and should be staggered at least two supports.

Lightly butt tongue and groove panel sides together and leave 1/8" (3 mm) gap at panel ends. Panel ends of single layer combination subfloor/underlayment should be lightly butted.

Use 2" (50 mm) or 6d deformed shank nails, 1-3/4" (45 mm) No. 10 screws or 2-1/2" (63 mm) or 8d common nails at 6" (150 mm) o.c. along panel edges keeping fasteners 3/8" (10 mm) away from panel edges. (Drywall screws are not recommended.) Space fasteners at 10" (250 mm) o.c. on intermediate supports for single layer floors and 12" (300 mm) o.c. for subfloors.

Lay panels across three or more supports, keeping the side marked "This Side Down" on the supports when using T&G panels. End joints must be made over the supports and should be staggered at least two supports.

Lightly butt tongue and groove panel sides together and leave 1/8" (3 mm) gap at panel ends. Panel ends of single layer combination subfloor/underlayment should be lightly butted.

Use 2" (50 mm) or 6d deformed shank nails, 1-3/4" (45 mm) No. 10 screws or 2-1/2" (63 mm) or 8d common nails at 6" (150 mm) o.c. along panel edges keeping fasteners 3/8" (10 mm) away from panel edges. (Drywall screws are not recommended.) Space fasteners at 10" (250 mm) o.c. on intermediate supports for single layer floors and 12" (300 mm) o.c. for subfloors. (Special instructions for fastening glued and nailed subfloors are available from manufacturers or the Structural Board Association.)

In addition, OSB is required to maintain its strength and stiffness performance when exposed to weather during long construction delays. OSB panels intended for construction are marked Exposure 1 for durability in accordance with voluntary product standard PS 2-92 (or Exterior Bond if stamped to meet CSA 0325).

Remember to gap OSB panels to allow for possible expansion.

Sheathing grade OSB subfloors are well suited for most floors and are intended to have an additional layer of flooring material such as an OSB underlayment panel, wood strip flooring or concrete topping.

Single Floor grade panels are used as combination subfloor/underlayment do not require an additional layer. The edges of Sheathing or Single Floor panels must be supported with approved tongue and groove joints or solid blocking.

Performance of OSB floor systems can be enhanced, if in addition to nailing, sheathing is glued to the joists with elastomeric glue and the tongue and groove edges are glued together.

Use of thicker subfloors or reduced fastener spacing will also enhance the performance of OSB floors.