Frequently Asked Questions

If you're wondering what happens when engineered wood products get wet on the job site, the short answer is that wood construction is durable and will normally be structurally sound after severe exposure to moisture. Structural plywood and OSB used in floors, walls and roofs are made with water-resistant adhesive and retain their strength following wetting events. Although the surface of the panels may be rough from water exposure, they generally remain structurally sound. However, panels saturated with water will feel less stiff than those in a dry condition. Until the panels dry, they should not be subjected to heavy loading, such as repeated heavy foot traffic or loaded drywall carts.

In cases of severe or unusually prolonged exposure, it may be necessary to retain the services of a qualified construction expert for panel evaluation.

For more information about engineered wood products that get wet on the job site, refer to APA’s FAQs: Questions About Wood Structural Panel Exposure to Excessive Moisture, Form X501.

If you're looking for APA-certified plywood, OSB or other engineered wood products near you, the APA Manufacturer Directory is the best place to start.

Visit the APA Manufacturer Directory to search for specific APA-trademarked engineered wood products produced by APA members across North America by country, state or province.

If you're using APA’s Wall Bracing Calculator to determine bracing requirements for your project, follow the basic steps below to create your wall lines and bracing segments.

To use the Wal Bracing Calculator:

• Click the input wall line information button

• Advanced to the wall line details and wall line segment details page of the calculator

• Create braced wall lines and bracing segments

Please note that APA’s Wall Bracing Calculator is intended for use by experienced designers that are familiar with wall bracing. Refer to the Wall Bracing Calculator Quick Start Guide, Form Q230, for basic instructions on using the calculator.

You can download APA Product Reports® for free on the Product Report section of the Technical Document Library on APA’s website.

APA Product Reports help building officials and design professionals determine a product's conformance with codes and national, international or industry-recognized standards. APA issues these reports to document the compliance of an engineered wood product that is manufactured under a quality program audited by APA. APA Product Reports signify the product's compliance with the relevant provisions in the model building codes.

Looking for APA Product Reports for use in Canada? These reports are denoted with a "C" at the end of the form number.

If you're looking for national standards for engineered wood products, APA publishes and maintains numerous standards covering manufacturing, testing, product performance and quality assurance. Learn more about APA’s involvement with standards publishing here or explore specific standards below.

Voluntary Product Standard PS 1-22, Structural Plywood, Form L870

Voluntary Product Standard PS 1-22 is the national standard for producing, marketing and specifying plywood for construction and industrial uses.

Voluntary Product Standard PS 2-18, Performance Standard for Wood Structural Panels, Form S350

Voluntary Product Standard PS 2-18 provides information on performance requirements, adhesive bond performance, panel construction and workmanship, dimensions and tolerances, marking, and moisture content of structural-use panels.

Performance Standards and Qualification Policy for Wood Structural Panels, Form E445

APA PRP-108 describes requirements and test methods for APA Performance Rated Panels.

ANSI/APA PRP 210-2024: Standard for Performance-Rated Engineered Wood Siding, ANSI/APA PRP 210-2024

This American National Standard provides requirements and test methods for qualification and quality assurance for performance-rated engineered wood siding, a veneer-based, structural-use product.

APA PRI-400 Performance Standard for Residential I-Joists, PRI-400

APA PRI-400 contains performance criteria, qualification requirements and quality assurance information for APA Performance Rated I-Joists used in residential floors.

APA PRI-400 Performance Standard for Residential I-Joists, Limit States Design for Canada, PRI-400 CA

APA PRI-400 CA contains performance criteria, qualification requirements and quality assurance information for APA Performance-Rated residential I-joists, limit states design, in accordance with the National Building Code of Canada.

APA PRI-405 Performance Standard for Commercial I-Joists, PRI-405

This standard provides requirements and design properties for APA Performance-Rated I-joists in sizes that are commonly used in nonresidential floor and roof construction.

ANSI/APA PRS 610.1: Standard for Performance-Rated Structural Insulated Panels in Wall Applications, PRS 610.1-2023

This Standard covers the manufacturing, qualification, quality assurance, design and installation requirements for performance-rated structural insulated panels (SIPs) used in wall applications.

ANSI/APA PRG 320-2025 Standard for Performance-Rated Cross-Laminated Timber, ANSI/APA PRG 320-2025

This Standard provides requirements and test methods for qualification and quality assurance for performance-rated CLT, which is manufactured from solid-sawn lumber or structural composite lumber.

ANSI / APA PRR 410-2021: Standard for Performance-Rated Engineered Wood Rim Boards, PRR 410

This Standard provides requirements and test methods for qualification and quality assurance for performance-rated engineered wood rim boards.

ANSI 117-2025: Standard Specification for Structural Glued Laminated Timber of Softwood Species, ANSI 117-2025

The Standard contains general information on structural glued laminated timber members that may be useful to the manufacturer and designer.

ANSI A190.1-2022 Product Standard for Structural Glued Laminated Timber, ANSI A190.1

This Standard contains requirements for the manufacture and quality control of structural glued laminated timber.

ANSI 405-2023: Standard for Adhesives for Use in Structural Glued Laminated Timber, ANSI 405-2023

This Standard provides minimum requirements to evaluate adhesives for use in structural glued laminated timber.

Yes, CARB regulations, H.U.D., and TSCA all explicitly exempt structural plywood specified to PS 1, structural panels specified to PS 2, OSB specified to PS 2, structural composite lumber specified to ASTM D5456, structural glued laminated timber specified to ANSI A190, and prefabricated wood I-joists specified to ASTM D5055. These exemptions apply to products trademarked or audited by APA under the APA quality assurance program, regardless of whether the product is used in a construction or industrial (manufacturing) application. Note that although CLT is not listed as an exempted product, CLT certified to ANSI/APA PRG 320 is made with moisture-resistant adhesives and has a low formaldehyde emission.

Find additional guidance in APA's publication Formaldehyde and Engineered Wood Products, Form J330, which addresses concerns related to engineered wood products and explains why they have such low emission levels that they are exempt from the leading formaldehyde emission standards and regulations.

Energy efficiency policies and building energy codes continue to evolve rapidly at the federal, state, and local levels, directly impacting residential and commercial construction practices. The International Energy Conservation Code (IECC) serves as the foundation for many state and local energy codes and influences construction practices, including wall assemblies, insulation requirements, air sealing, continuous insulation, and overall building envelope performance. APA supports practical, cost-effective energy solutions that maintain design flexibility, affordability, constructability, and durability for builders and designers. Engineered wood products play a critical role in high-performance wall, floor, and roof systems by supporting durable assemblies, advanced framing techniques, and efficient insulation strategies. Learn more about engineered wood’s important role in Energy Efficiency and how APA advocates on behalf of building professionals for flexible compliance approaches that allow builders to meet energy goals using a variety of compliant and proven engineered wood assemblies.

From a structural or durability point of view it doesn’t make any difference which side of a plywood wood structural sheathing panel is placed "up" or out."

The comments listed are strictly serviceability related and traditionally understood to be outside of the scope of building code governance.

The stamped side of roof sheathing panels often goes down so the inspector can more easily access the grade stamp with the panels in place.

Many manufacturers provide a "this side up" stamp to indicate the appropriate face. This kind of stamp also finds its way on panels with asymmetrical tongue and groove edges. In this case, all of the stamps should face up or down so the T&G joints fit flush. Traditionally, the grade stamp goes on the bottom to prevent the possibility of ink bleed through from discoloring vinyl flooring and to allow the inspector to access the grade stamp after the finished flooring is in place. As with sheathing, there is no structural or exposure durability consideration for placing either side of a panel up or down.

The same is true for wall sheathing applications; there is no structural or durability reason for either side of the panel to be in or out. However, roof sheathing framers often place the stamped side facing in to facilitate framing inspection.

If you're concerned about formaldehyde in OSB, APA-trademarked plywood and OSB are not manufactured using urea formaldehyde adhesives.

APA-trademarked plywood or OSB (APA Rated Sheathing and APA Rated Sturd-I-Floor®) conforming to US Standards PS 2 or APA Standard PRP-108 are produced with phenolic adhesives. Some OSB conforming to PS 2 and PRP-108 are also produced with polymeric methylene diphenyl diisocyanate (pMDI) adhesive exclusively, or with phenolic adhesive in the face and back layers and pMDI in the core layer. APA Rated Sheathing and APA Rated Sturd-I-Floor panels are NOT produced using urea formaldehyde adhesive because it is not sufficiently water resistant for wood structural panel applications.

For additional information, refer to item 3 under “U.S. and Canadian Formaldehyde Regulations Applicable to Engineered Wood Products” in APA publication J330, Technical Note: Formaldehyde and Engineered Wood Products.

If you're wondering how much moisture exposure I-joists can tolerate, they are intended for dry-service applications and should not be permanently exposed to weather or elevated moisture levels.

I-joists must not be used in applications where they will be permanently exposed to weather or reach a moisture content of 16% or greater. I-joist can withstand normal exposure, but excessive exposure during distribution, storage or construction may lead to cupping, bowing or expansion beyond manufacturing tolerances. Find additional guidance in the APA publications below.

• APA Performance Rated I-Joists Storage, Handling & Safety Recommendations

• Proper Storage and Handling of I-Joists and LVL

The racking resistance of APA plywood or OSB wall bracing panels and the lateral load capacity of a shear wall for wind and seismic loading is not affected by the orientation of the sheathing panels. Panels may be installed with the long, or strength, axis either horizontal or vertical. However, all panel edges of shear wall sheathing must be attached to framing or blocked unless designed as an unblocked shear wall.

The IRC requires blocking horizontal panel joints of wood structural panel sheathing for wall segments counted as bracing; however, blocking may be omitted where bracing length is at least twice the minimum required. For this reason, many designers and builders prefer to install sheathing with the long axis vertical, thus avoiding the need for additional horizontal blocking.

If you're wondering whether the rough or smooth side of an OSB wood structural sheathing panel should face "up" or "out," it generally makes no structural or durability difference.

The comments listed are strictly serviceability related and traditionally understood to be outside of the scope of building code governance.

The stamped side of roof sheathing panels often goes down, so the inspector can more easily access the grade stamp with the panels in place. Note that many OSB producers make their sheathing panels with one rough and one smooth side. On steep roofs, the rough side goes up to provide a more secure working surface.

Many OSB Sturd-I-Floor® manufacturers provide a “this side up” stamp to indicate the appropriate face. This kind of stamp also finds its way on panels with asymmetrical tongue-and-groove edges. In this case, all of the stamps should face up or down so the T&G joints fit flush.

Traditionally, the grade stamp goes on the bottom to prevent the possibility of ink bleed through from discoloring vinyl flooring and to allow the inspector to access the grade stamp after the finished flooring is in place.

The same is true for wall sheathing applications; there is no structural or durability reason for either side of the panel to be in or out. However, roof sheathing framers often place the stamped side facing in to facilitate framing inspection.

If you're trying to determine which fire protection method is acceptable for your I-joists, start by identifying your specific product and reviewing APA System Report 405. APA System Report 405 describes a number of assemblies listed as FP-01 through FP-12.

You can also refer to APA Product Reports^® for I-joist products. These reports describe fire protection assemblies, including which FP description can be used on their various I-joist products.

If you're planning a moisture-resistant foundation, the design and construction practices below can help manage water and reduce moisture-related problems.

• Determine frost depth and protection requirements

• Identify and design for expansive soils

• Identify the presence of hydrostatic pressure

• Site layout

• Install a footing drain

For detailed information, refer to APA’s Build a Better Home: Moisture-Resistant Foundation Construction, Form A520.

Holes are allowed in engineered wood beams, I-joists and APA Rim Board when properly located. It is important to understand that field notches and holes reduce the published design value of the member, but when located in accordance with APA or manufacturer published literature, they are permitted. Hole sizes and/or locations that fall outside the scope of published tables may also be acceptable, based on analysis of actual hole size, span, spacing and loading conditions. The effects of any field notching on the edges of beams and I-joists is more severe and should be verified by the beam manufacturer or checked by the designer.

For more information, refer to APA publications:

• Technical Note: Field Notching and Drilling of Glued Laminated Timber Beams, Form S560

• Technical Note: Effect of Large Diameter Horizontal Holes on the Bending and Shear Properties of Structural Glued Laminated Timber (Glulam), Form V700

• Technical Note: Field Notching and Drilling of Laminated Veneer Lumber, Form G535

• Technical Note: Effect of Large Diameter Horizontal Holes on the Bending and Shear Properties of Laminated Veneer Lumber (LVL), Form V900

• Performance Rated I-Joists Design and Construction Guide, Form Z725

If your jobsite gets wet during construction, the effects on engineered wood products depend on the severity and duration of the moisture exposure. Wood naturally contains some moisture within its cellular structure. The moisture content of wood products, both during construction and in-service, depends on variables including exposure to direct wetting, accumulated moisture, temperature, relative humidity and the drying potential of the system in which the wood is contained.

There are many factors that affect the durability of wood structural panels and each situation is unique. Therefore, it is impractical to define an acceptable moisture exposure due to construction delays under all circumstances. Factors such as geographical location, seasonal weather patterns and local weather history should be considered. Likewise, construction conditions that cause accumulation or dissipation of moisture will influence the effects on the panels. The longer panels are exposed and the more severe the exposure, the greater the effect on the panel performance. Although it is a function of both time and severity of moisture exposure, panels that are exposed to long construction delays may be unaesthetic yet remain structurally sound.

Once a structure is complete, wood normally stabilizes to an in-service moisture content between 6 and 14%. At these low levels, moisture content has negligible impact on the strength, stiffness or durability of wood products. However, accumulated moisture can lead to decay and mold growth if moisture content remains high (approximately 20 to 25% or higher) for a prolonged period.

Oriented strand board (OSB) and plywood panels exposed to moisture conditions for extended periods may exhibit a rough, uneven surface, some lifting or flaking of surface strands on OSB or thickness swelling. Tests show, however, that swelling and flaking does not result in a loss of panel structural capacity after the panel dries to in-service moisture conditions. Exposure 1 and Exterior panels are subject to reductions in design values when in-service moisture will be 16% or greater.

For more information, refer to APA publications:

• FAQs: Questions About Wood Structural Panel Exposure to Excessive Moisture, Form X501

• FAQs: Questions About Structural Plywood and OSB Performance, Form F505

• Technical Topics: Wood Moisture Content and the Importance of Drying in Wood Building Systems, Form TT-111

• Technical Topics: Moisture Exposure Recommendations for Wood Structural Panels, Form TT-002

• Build A Better Home: Controlling Mold and Mildew, Form A525

• Decay of Engineered Wood Products, Form W505

• Technical Note: Controlling Decay in Wood Construction, Form R495

• Technical Note: Prevent Callbacks in Wood Flooring Installation, Form T350

If you're looking for advanced framing details, APA’s Advanced Framing Construction Guide, Form M400, provides construction details that may be used to save money and energy, as long as they do not negate the prescriptive requirements of local and regional structural code provisions.

If you're wondering how the APA product evaluation process works, the process follows a structured series of reviews, testing and quality verification steps to document compliance with applicable codes and standards.

The process begins with an initial review of your product and production process to define an evaluation plan and quality program. Next, products are sampled by APA and subsequently evaluated against applicable building codes, recognized standards, or third-party criteria. APA also verifies that your manufacturing processes meet established in-plant quality control requirements.

Following evaluation, APA issues an APA Product Report^®, along with a certification document and lab report to document compliance. Certain products may require ongoing inspection and periodic verification. Final product evaluation reports are published online, giving building officials and design professionals free, convenient access to your product documentation.

View APA Product Evaluation Reports

You can download APA Product Reports® for free on the Product Report section of the Technical Document Library on APA’s website.

APA Product Reports help building officials and design professionals determine a product's conformance with codes and national, international or industry-recognized standards. APA issues these reports to document the compliance of an engineered wood product that is manufactured under a quality program audited by APA. APA Product Reports signify the product's compliance with the relevant provisions in the model building codes.

Looking for APA Product Reports for use in Canada? These reports are denoted with a "C" at the end of the form number.

A performance-rated product is evaluated based on how it performs in structural applications rather than solely by wood species or prescriptive construction methods. APA performance ratings are developed through testing, engineering analysis, manufacturing qualification, and ongoing quality verification to help support consistent performance and code compliance.

An ANSI-approved standard is developed through a formal consensus process approved by the American National Standards Institute (ANSI) and follows the Due Process Requirement for American National Standards. That process is designed to ensure standards are created openly and fairly, with balanced participation from manufacturers, engineers, testing agencies, regulators, code officials, and other stakeholders.

ANSI approval does not mean ANSI writes the standard itself. Instead, it confirms that the standards developer—in this case APA—follows established procedures for transparency, consensus, appeals, and technical review.

For manufacturers and specifiers, ANSI-approved standard provides confidence that the standard represents broadly accepted industry requirements rather than the interests of a single organization or company.

APA maintains accreditations from organizations including ANSI National Accreditation Board (ANAB), Standards Council of Canada (SCC), Florida Department of Business and Professional Regulation (DBPR), City of Los Angeles, and Japan's Ministry of Agriculture, Forestry and Fisheries (MAFF).