Building Fire-Rated Systems

In many cases, ordinary wood-frame construction with wood structural panel sheathing provides ample fire resistance and is acceptable. When unusual circumstances require additional protection, the following options may be used:

• Protected construction: This includes any standard wood-frame assembly (floor, ceiling or wall) with a fire-resistive material such as gypsum wallboard, plaster or acoustical tile added to protect the wood members from flame passage and temperature rise.

• Heavy Timber Construction (Type IV-HT): Large wood members char slowly during a fire, acting as insulation and allowing the word beneath to continue supporting its load.

• Mass Timber Construction (Types IV-A, IV-B, IV-C): This method uses structural elements like cross-laminated timber (CLT) that meet minimum cross-section dimensions defined by the International Building Code (IBC), with noncombustible protection applied directly to the mass timber to achieve required fire-resistance ratings.

• Fire-Retardant-Treated (FRT) Wood: FRT wood reduces surface flame spread and can qualify for use in place of noncombustible materials in certain applications. However, it does not increase fire resistance. Fire-retardant treatments may affect span ratings and load capacities for APA-trademarked plywood. Consult the treating company for structural performance data.

• Fire-Retardant (FR) Paints: Proprietary coatings can reduce the flame-spread rating of plywood for nonstructural interior-finish applications such as wall and ceiling paneling. Some formulations are also available for exterior use.

• Sprinkler Systems: Installing an automatic sprinkler system can allow code requirements for flame spread and fire-resistance ratings to be relaxed, may enable additional building stories or increased floor area, and typically results in lower insurance premiums that offset installation costs within a few years.

For complete guidance on all protection methods, download APA’s Fire-Rated Systems Design and Construction Guide, Form W305.

Wood-frame wall systems can achieve one- and two-hour fire-resistance ratings through protected construction — combining standard stud framing and APA-Certified wood structural panels with fire-resistive materials such as gypsum wallboard and mineral wool insulation.

• One-Hour Load-Bearing Exterior and Interior Wall Assemblies: Multiple one-hour rated assemblies are available for both exterior and interior load-bearing walls using APA-Certified wood structural panels with gypsum wallboard, insulation and standard stud framing.

• Two-Hour Load-Bearing Wall Assemblies: Two-hour rated interior wall assemblies are achievable with 2x6 studs, mineral wool insulation and two layers of 5/8" Type X gypsum wallboard.

For complete guidance on building fire-protected wall systems, download APA’s Fire-Rated Systems Design and Construction Guide, Form W305.

Code accepted roof and floor systems that provide maximum strength and economy include numerous constructions with wood structural panels over a variety of support systems.

Refer to APA’s Fire-Rated Systems Design and Construction Guide, Form W305 and Engineered Wood Construction Guide, Form E30 for specific assembly details, UL design numbers, specifications and complete design guidance.

• Glulam performs exceptionally well in fire. Wood chars at a rate of only 1-1/2 inches per hour and the char itself protects the wood beneath, allowing properly designed glulam members to continue supporting loads without fire-retardant treatment. This is true even at temperatures exceeding 1,650°F, where unprotected steel members typically buckle and collapse.

• When fire-resistance ratings are required, glulam beams and columns can be designed and manufactured to achieve one- or two-hour ratings by adjusting member dimensions and lamination layup. Specifications should always be verified by a professional designer for compliance with local codes.

• After a fire, glulam members can often be salvaged. Depending on fire severity and following structural re-analysis by a qualified professional, it may be possible to remove the damaged material and refinish the surface.

• APA does not currently recommend fire-retardant-treated glulam, as treatment may cause checking or affect strength and stiffness. Designers considering FRT glulam should request a code report for approval.

Refer to APA’s Technical Note: Calculating Fire Resistance of Glulam Beams and Columns, Form Y245 for detailed information on calculating fire resistance of glulam beams and columns.