A High-Performance Advantage

I-Joist Basics

I-joists are strong, lightweight, "I" shaped engineered wood structural members that meet demanding performance standards. I-joists are comprised of top and bottom flanges, which resist bending, united with webs, which provide outstanding shear resistance. The flange material is typically laminated veneer lumber (LVL) or solid sawn lumber, and the web is made with plywood or OSB. The robust combination of structural characteristics results in a versatile, economical framing member that is easy to install in residential and light commercial projects.

Common I-Joist Applications

I-joists are used extensively in residential floor and roof framing. They are ideal for long spans, including continuous spans over intermediate supports. Because I-joists are straight and true, it's easier for builders to avoid crowning and maintain a level framing surface. In addition, wood I-joists are typically stocked and readily available in depths that meet the needs of residential framing.

Common Depths

9-1/2", 11-7/8", 14", 16". Flange widths vary from 1-1/2" to 3-1/2"; long lengths are readily available.

Common Uses

I-joists are popular for floor and roof framing. Many APA member-manufacturers have software design tools; contact the manufacturer (at right) for more information. 


APA Performance Rated I-joists (PRIs) are manufactured in accordance with APA PRI-400, Performance Standard for Residential I-joists. This Performance Standard provides an easy-to-use table of allowable spans for applications in residential floor construction, allowing designers and builders to select and use I-joists from various member manufacturers using just one set of span tables. APA PRIs are recognized through ICC-ES ESR-1405.

The APA Mark of Quality

APA trademarks appear only on products manufactured by APA member mills. The mark signifies that product quality is subject to verification through APA audit—a procedure designed to assure manufacture in conformance with APA performance standards or the standard shown in the mark.

I-Joist Publications

APA Performance Rated I-Joists

Includes information on span ratings, installation details, cantilever designs, architectural specifications and engineering design properties for APA Performance Rated I-Joists.

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Resource Library

Access a complete list of APA publications about I-joists in APA's Resource Library.

Fire Protective Assemblies for Wood I-Joist Floors

Learn about several options that enhance the fire performance of I-joist floor systems and comply with the International Residential Code (IRC) by visiting the I-Joist Fire Assemblies page.

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Technical Topics TT-015: Wood I-Joist Floors, Firefighters and Fire

A discussion of the durability and safety of wood I-joist floor assemblies in structure fires. Includes APA’s recommendation to increase the fire endurance of all floor-joist assemblies based on the International Building Code.

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Technical Topics TT-126: Applicability Of APA Trademarks On Engineered Wood Products Surface-Coated With Fire Protective Coatings

Contains Q&A concerning fire protective coatings. Certification and inspection of products treated with fire-protective coatings are outside the scope of APA.

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White Paper: Basis of IRC Membrane Protection Provisions

APA, AWC and WIJMA jointly developed this paper that describes the history, background and intent of the IRC provisions for fire protection of floors as well as the methods used for establishing equivalence and compliance with these fire protection requirements.

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White Paper: Code Requirements for Prefabricated Wood I-Joists

APA, AWC and WIJMA jointly developed this paper that describes the basic code recognition for prefabricated wood I-joists and the need for product certification in compliance with the codes.

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White Paper: Fire Protection of I-Joist Floors with Factory-Applied Solutions

APA developed this paper that describes the basic fire protection requirements for prefabricated wood I-joists with factory-applied fire protection solutions for compliance with the codes.

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