Structural Performance, Layer by Layer
Plywood is manufactured from thin layers of cross-laminated wood veneer bonded under heat and pressure to form a strong, stable structural panel. Trusted by builders and designers for more than a century, it remains one of the world’s most widely used and reliable construction materials.
Designers and builders choose plywood for its proven structural performance, construction efficiency, and long-term reliability across a wide range of building applications.
Key benefits include:
High Strength-to-Weight Ratio – Strong, efficient assemblies without unnecessary material weight
Dimensional Stability – Cross-laminated construction resists warping, cracking, splitting, and shrinkage
Excellent Fastener Holding – Consistent, reliable fastening performance
Strength in Both Directions – Simplifies design, layout and installation
Verified Performance & Quality Assurance – APA-trademarked panels carry clear ratings for span, exposure durability, and code compliance
Construction Efficiency – Installs quickly with standard tools and integrates easily with other building systems.
Plywood is one of the most versatile engineered wood products, supporting a wide range of structural, interior, exterior, and industrial construction needs.
APA-trademarked plywood is engineered for consistent performance and long-term reliability across critical building applications, including:
Subflooring
Single-layer floor systems
Wall sheathing
Roof sheathing
Ceiling and deck sheathing
Siding and soffits
Marine construction
Concrete formwork
Mezzanine floors and shelving
Furniture manufacturing
Industrial containers
Trailer liners
Recreational vehicle floors, roofs, and components
Materials-handling applications
Its broad performance range and predictable behavior make plywood a foundational material for designers, builders, and manufacturers across virtually every construction sector.
When selecting plywood for your project, several key attributes—identified in the APA trademark on each panel—determine which product best meets your needs.
For complete design capacities, engineering calculations, capacity tables, section properties, technical specifications and how to read APA trademark stamps, download D510 - Panel Design Specification.
D510 - Panel Design Specification
Understanding the APA trademark ensures you select plywood that meets the demands of your project.
View Plywood Trademark Examples
Standards – Plywood is manufactured to prescriptive standards (PS 1) or performance standards (PS 2, APA PRP-108). Panels carry Performance Category and decimal thickness designations for building code reference.
Veneer – Wood species are classified into five strength groups (Group 1 strongest), with over 70 species rated under PS 1. Veneer grades range from A (smooth, paintable) to D (utility grade), defining appearance and allowable repairs.
Panel & Appearance Grades – Grades indicate veneer quality on face and back (A-B, B-C) or intended use (Rated Sheathing, Rated Sturd-I-Floor). Surface finishes include unsanded, touch-sanded, fully sanded, or overlaid (HDO/MDO) depending on application.
Bond Classifications – Exterior panels withstand long-term weather exposure. Exposure 1 panels (including "CDX") resist construction moisture but aren't suitable for permanent outdoor exposure.
Span Ratings – Ratings show maximum recommended spacing between supports. Sheathing shows two numbers (32/16 for roof/subfloor), single floor shows one number, wall sheathing typically marked W24.
Code Provisions – Design values and recommendations align with U.S. building codes. For engineered applications, document D510, Panel Design Specification, provides detailed capacity tables, section properties, and adjustment factors.
Mechanical Properties – Plywood panels have distinct strength and stiffness properties based on their layered construction. Key properties include bending stiffness and strength, axial tension and compression, shear capacity, and bearing strength. These vary by panel thickness, span rating, and stress direction relative to the strength axis.
Load-span tables provide uniform load capacities (in pounds per square foot) for plywood panels used in various construction applications. These engineering design tools show maximum allowable loads based on specific span distances, deflection criteria, and support conditions. Unlike basic span ratings that provide general recommendations, load-span tables allow designers to calculate precise load capacities for conditions not covered in standard construction guides.
For complete load-span tables, adjustment factors, and design examples, download Q225 - Load-Span Tables for APA Wood Structural Panels.
Q225 - Load-Span Tables for APA Wood Structural Panels
Load-span tables calculate allowable loads based on deflection limits (L/360, L/240, L/180), bending strength, shear strength, and span conditions (one, two, or three supports). Tables provide values for various support spacings and strength axis orientations. The actual allowable load is the lowest value among deflection, bending, and shear calculations.
Tables are organized by panel type and grade:
Plywood Sheathing – Standard and Structural I grades
Plywood Sturd-I-Floor – Standard and Structural I single-floor panels
Sanded Plywood – Group 1 panels with adjustments for other species groups
Values assume dry conditions, normal load duration, and multi-span applications. Adjustment factors are provided for moisture exposure, load duration (snow, wind, earthquake), and single-span conditions.
APA member manufacturers produce plywood that meets rigorous, independently verified performance and quality requirements. Membership signifies a commitment to consistent manufacturing, third-party oversight, and products designed to perform in real-world structural applications.
Manufactured to recognized U.S. and Canadian standards
Subject to ongoing quality assurance and product testing
Produced by companies with proven expertise in engineered wood products
Supported by APA technical resources, evaluation, and industry oversight
Use the APA manufacturer directory to locate member manufacturers and explore the range of plywood and other engineered wood products they produce.
Space Sheathing Right to Reduce Callbacks
Learn how to prevent buckling with proper 1/8 inch spacing to reduce callbacks. Watch this 46-second video, or print or download the Builder Tip PDF in English or Spanish.
46 Seconds
Wood Structural Panels as an Air Barrier
56 minutes
Minimize Nail Pops
Nail pops occur when lumber shrinks after installation, causing nail heads to protrude. Repeated moisture changes can worsen the issue over time.
Proper Selection and Installation of APA Plywood Underlayment
This publication provides an overview of selection, handling, installation and fastening of APA plywood underlayment.
PDF, 3 pages
Standards - L870
This publication is the national standard for performance requirements and marking plywood for construction and industrial uses.
Product Guide - F405
This product guide describes performance standards, applications, trademark and performance category information for APA Performance Rated Panels
Excerpt - E30X-PSS
This publication is an excerpt from the APA Engineered Wood Construction Guide, providing product descriptions and specification recommendations for wood structural panels
Plywood manufacturing standards follow two main approaches:
Prescriptive standards – Specify the recipe for panel construction (veneer species, number of plies, thickness, orientation)
Performance standards – Define required performance levels for end uses rather than manufacturing details, allowing plywood to be rated alongside other wood structural panels like OSB
Standards can also be categorized as:
Consensus-based – Developed through committees with broad industry input following recognized procedures
Proprietary – Developed by individual companies or industry groups (may later become consensus standards, such as APA PRP-108 described below)
PS 1 – Structural Plywood – Voluntary Product Standard originating in 1966, combining earlier U.S. Commercial Standards. Originally prescriptive, but added performance-based provisions in 1983 for sheathing and single-floor grades. Recognized in all U.S. model and local building codes.
PS 2 – Performance Standard for Wood Structural Panels – Voluntary Product Standard that was the first consensus-based performance standard (1992), applying to plywood and other wood structural panels including OSB and composite panels. Covers sheathing and single-floor grades with performance criteria and test methods. Recognized in all U.S. building codes.
CSA O121 and CSA O151 – Canadian Plywood Standards – Consensus-based Canadian standards governing the manufacture and performance of Douglas Fir plywood (O121) and Canadian Softwood Plywood (O151). Plywood manufactured in Canada to these standards may also bear the APA trademark when produced by APA member mills under APA quality assurance programs.
APA PRP-108 – Performance Standards and Qualification Policy for Wood Structural Panels – Prototype proprietary performance standard (1980) that became the foundation for PS 2. Includes provisions for sheathing, single-floor, and siding grades. Allows faster adoption of technical developments than consensus standards.
ANSI Standards – ANSI/APA standards are nationally recognized, consensus-based standards developed by APA and approved by the American National Standards Institute. They establish performance requirements for engineered wood panel products, supporting consistent quality, structural performance, and appropriate use in construction.
ANSI/APA PRP 210 – Standard for Performance-Rated Engineered Wood Siding – establishes performance requirements for performance-rated engineered wood siding, including plywood siding products.
Since 2008, plywood panels are labeled with both:
Performance Category – Links to nominal thicknesses used in building codes (IBC, IRC)
Decimal thickness designation – Meets packaging/labeling regulations
The Performance Category serves as the "nominal panel thickness" in building codes and is the primary designation used throughout the industry.
Learn more about Performance Category and thickness labeling requirements in APA publication TT-054, Technical Topic: Panel Thickness Tolerances and Labeling.
Panel Thickness Tolerances and Labeling
For complete technical details, including recommended design capacities (ASD) and design methods for plywood panels manufactured under Voluntary Product Standards PS 1 and PS 2 and APA Performance Standard PRP-108, download publication D510 - Panel Design Specification.
Wood veneer is the core structural element of plywood. Veneer selection, grading, and arrangement directly influence panel strength, stiffness, appearance, and end-use suitability.
Plywood veneer species are classified into five species groups based on relative strength and stiffness
Group 1 contains the strongest species, with strength decreasing as group numbers increase
Species group identification appears in the APA trademark on non–span-rated panels, primarily sanded grades
When face and back veneers differ, the lower-strength group governs for structural purposes
See Table 1: Classification of Species on page 6 in D510 – Panel Design Specification for complete species group classifications
Veneer grades define appearance characteristics and allowable repairs
Grades range from A (highest appearance quality) through D
C-grade veneer is the minimum permitted for Exterior plywood
D-grade veneer is limited to panels intended for applications protected from long-term weather exposure
See Table 2: Veneer Grades in D510 – Panel Design Specification for detailed veneer grade descriptions
Veneers are assembled in cross-laminated layers with alternating grain directions
This construction:
Distributes strength and stiffness in both panel directions
Improves dimensional stability
Reduces shrinkage and swelling compared to solid wood
For complete veneer grade definitions, species group classifications, and their role in structural performance, see APA publication D510 – Panel Design Specification.
Plywood panels are identified by grade designations that reflect veneer appearance, surface finish, and intended end use. These grades help specifiers and builders select panels that balance appearance requirements with structural performance.
Panel grades are commonly identified by the veneer grades used on the face and back (e.g., A-B, B-C)
Some panels are identified by end-use designations rather than veneer grades, such as:
APA Rated Sheathing
APA Rated Sturd-I-Floor® (Single Floor)
Used where surface appearance is not critical, such as roof, wall, and subfloor applications
Classified by span rating, which governs structural performance
Design capacities are based on span ratings rather than veneer appearance
Lightly sanded to improve thickness uniformity
Common grades include:
Underlayment
Single floor
C-D Plugged and C-C Plugged
Panels intended for single-floor applications are typically tongue-and-groove and span rated
Panels with B-grade or better faces are sanded smooth during manufacture
Overlaid panels (MDO and HDO) are produced for applications requiring durable, uniform surfaces
Structural design capacities for these panels are based on Performance Category and assumed face veneer species group
For detailed panel grade definitions, surface classifications, and design assumptions, refer to D510 – Panel Design Specification. For a summary of panel grade designations, typical APA trademarks, and intended applications, see Table 3: Guide to APA Performance Rated Panels.
Bond classification describes the moisture resistance of the adhesive bond used in plywood panels. It is an indicator of exposure suitability—not a measure of structural strength or decay resistance.
Wood structural plywood is manufactured in two bond classifications:
Exterior
Designed to withstand repeated wetting and drying or long-term exposure to weather
Intended for applications subject to permanent exposure
Exposure 1
Suitable for uses not involving long-term exposure to weather
Designed to resist moisture effects during construction or in similarly limited exposure conditions
Uses the same exterior-type adhesives as Exterior panels, but other panel factors limit long-term exposure performance
Species group identification appears in the APA trademark on non–span-rated panels, primarily sanded grades
When face and back veneers differ, the lower-strength group governs for structural purposes
See Table 1: Classification of Species in D510 – Panel Design Specification for complete species group classifications
Bond classification does not affect strength, stiffness, or span rating when panels are used as intended
Bond classification does not provide resistance to fungal decay
Decay resistance depends on proper design, detailing, construction practices, and maintenance
Panels commonly referred to as “CDX” are Exposure 1, not Exterior, and should only be used where long-term weather exposure is not expected
For a summary of panel grades, typical APA trademarks, and permitted bond classifications, see Table 3: Guide to APA Performance Rated Panels in D510 – Panel Design Specification.
Span ratings identify the maximum recommended spacing of supports for plywood panels used in code-conforming construction. Span ratings appear in the APA trademark and are a primary factor in panel selection.
Span ratings apply when the strength axis (long panel dimension unless otherwise marked) is placed across supports
Ratings are expressed in inches on center
The rating applies to normal loading conditions consistent with building codes
Panel capacities and span ratings depend on load direction relative to the panel strength axis (see Figure 2: Panel Strength Axis of D510 – Panel Design Specification).
Sheathing span ratings are shown in the APA trademark stamp on the panel as two numbers separated by a slash (e.g., 32/16, 48/24)
First number – Maximum support spacing for roof sheathing
Second number – Maximum support spacing for subflooring
Example:
A 32/16 panel may be used over:
Roof supports up to 32 in. o.c.
Floor supports up to 16 in. o.c.
Some roof spans require panel edge support to achieve rated performance
Wall-only panels are identified as Wall-24 (W24)
The number indicates the maximum wall stud spacing
These panels may be installed with either panel axis across supports
Single Floor panels carry one span rating (e.g., 20 oc, 24 oc)
The rating reflects the maximum floor joist spacing
A floor span rating of “20” corresponds to an end-use span of 19.2 inches
For panel grade examples, typical APA trademarks, and common span ratings, see Table 3: Guide to APA Performance Rated Panels in D510 – Panel Design Specification.
View Panel Design Specification
Span ratings establish support spacing, while load-span tables provide recommended uniform load capacities
APA Technical Note Q225 – Load-Span Tables for APA Wood Structural Panels includes:
Uniform load limits for plywood panels by span rating
Loads governed by deflection, bending, and shear
Tables derived from design capacities in D510 – Panel Design Specification
These tables support engineering-based evaluation when loading conditions require additional analysis
Plywood manufactured and trademarked in accordance with applicable standards is recognized for structural use in building codes. Code provisions reference plywood through product standards, performance requirements, and installation assumptions.
Plywood manufactured under Voluntary Product Standards PS 1 and PS 2 are recognized in:
International Building Code® (IBC)
International Residential Code® (IRC)
Codes reference plywood by:
Panel grade
Span rating
Performance Category (used as nominal panel thickness)
Code provisions assume installation consistent with:
Strength axis orientation
Support spacing
Fastening and edge support requirements
Plywood manufactured to applicable Canadian CSA standards is recognized in the National Building Code of Canada (NBCC)
APA-trademarked panels manufactured in Canada may reference CSA standards as part of the panel mark
Canadian codes similarly rely on span ratings, panel grades, and intended end use
Code recognition is based on panels being specified, installed, and detailed properly
Deviations from recommended span, fastening, or exposure conditions may require additional engineering evaluation
For project-specific requirements, refer to the applicable building code, along with APA publication D510, Panel Design Specification for panel rating conventions, span assumptions, and design conditions.
Mechanical properties describe how plywood resists loads and deforms in service. These properties form the basis for structural design values published in D510 – Panel Design Specification.
View Panel Design Specification
D510 provides design information derived from plywood’s key mechanical properties, including:
Bending strength and bending stiffness
In-plane shear strength
Shear through the panel thickness
Deflection under uniform load
Mechanical properties are expressed as tabulated design capacities, not raw material test values
Values are organized by:
Panel grade and span rating
Performance Category
Direction of loading relative to the panel strength axis
Published capacities represent conservative, code-consistent minimums applicable to permitted panel constructions
D510 includes:
Adjustment factors for load duration, moisture, and creep
Guidance for evaluating both strength and deflection
Design examples showing application of mechanical property–based capacities
For complete mechanical property–based capacities and supporting design guidance, refer to APA publication D510 – Panel Design Specification.
The APA trademark stamp is a quality and performance mark that verifies an engineered wood product meets recognized industry standards. On plywood, the stamp identifies the applicable product standard, intended structural application, and key performance characteristics needed for proper specification and use.
For a comprehensive collection of APA plywood trademark stamp examples, including performance-rated panels and application variations, refer to Specification Guide E30 Excerpt: Panel Selection and Specification. The guide provides detailed illustrations and explanations to support proper identification and specification.
When plywood is performance-rated, it is manufactured to meet official U.S. standards and verified for structural performance — including load-carrying capacity for specific end uses.
Learn More About Performance Ratings How to Read an APA Trademark Stamp
Refer to APA publications F505 & X501 for information related to wood structural panels and exposure to moisture.
Form F505, FAQs: Questions About Structural Plywood and OSB Performance – Answers questions about panel performance, grade, growth or natural characteristics.
Form X501, FAQs: Questions About Wood Structural Panel Exposure to Excessive Moisture – This document provides guidance about the serviceability of wood structural panels (plywood and oriented strand board [OSB]) after exposure to high levels of moisture.
For availability, check out your local lumber yard or retailers in your area, or browse APA-certified plywood manufacturers.
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.
APA-trademarked plywood (APA Rated Sheathing and APA Rated Sturd-I-Floor) conforming to US Standards PS 1 or APA Standard PRP-108 are produced with phenolic adhesives. 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.
To read and use APA span/load tables for floor or roof joists, consult the APA Engineered Wood Construction Guide, Form E30. For guidance on selecting the appropriate panel based on spans and loads, refer to the Panel Selection section of that guide. Once you've identified the right panel, the Roofs and Floors section contains the detailed span and load tables you'll need for both applications.
SIZED FOR SPACING is a notation often found in APA Rated Sheathing, APA Rated Sturd-I-Floor, and APA Rated Siding trademarks, indicating that the manufacturer has produced the panel to a size slightly less than the traditional nominal 48 inches by 96 inches. This is done to facilitate proper panel spacing during construction. The use of the notation is not required when a panel is so manufactured, but some manufacturers use the notation as a courtesy to the customer. Find additional information in APA publication TT-055, Technical Topics: Sized for Spacing.