Builders choose I-joists because they help reduce callbacks by eliminating squeaks and vibration. They are readily available and easy to install, especially for long spans, including continuous spans over intermediate supports. Plus, builders have many options when it comes to constructing code-compliant I-joist floor assemblies.
Some states and jurisdictions have updated their requirements related to floor systems. Both the 2012 and 2015 versions of the International Residential Code (IRC) include provisions to enhance the fire performance of floor systems when residential sprinklers are not used. For example, the IRC requires that the bottom of all residential floor assemblies, with a few exceptions, be covered with drywall or have some other means of fire protection. There are several alternative ways to meet these IRC provisions. APA’s System Report SR-405 details seven assemblies that can be used in jurisdictions where 2012 IRC Section R501.3 or 2015 IRC Section R302.13 have been adopted.
Easy, Cost-Effective Options for I-Joist Floor Assemblies
While all seven assemblies in APA System Report SR-405 meet code requirements, APA encourages builders to consider the newly introduced Options 6 and 7 which combine efficient fire protection with quick, easy installation:
- SR-405 Option 6: 1/2-inch gypsum board installed on top of the bottom flange (used with a maximum joist spacing of 19.2 inches or less on center)
- SR-405 Option 7: 5/8-inch gypsum board installed on top of the bottom flange (this is the same configuration as Option 6, with slightly thicker gypsum when the I-joist spacing is up to 24 inches)
Both assemblies allow builders to take advantage of all of the performance benefits of I-joist floor assemblies, including improved fire protection. Gypsum panels are simple to install and easy to temporarily remove when necessary to reach wiring, plumbing and mechanical systems. No fasteners or glues are required, which allows quick installation and access to the space above the panels. The systems also hide plumbing, wiring and ductwork in the floor cavity, creating a finished ceiling appearance.
Download APA System Report SR-405.
APA System Report SR-405: Fire Protection of Wood I-Joist Floors
Expanded in November 2015, APA System Report SR-405 provides several practical systems for design and construction of fire-resistant floor assemblies built with prefabricated wood I-joists that satisfy the requirements of IRC Section R501.3. APA System Report SR-405: Fire Protection of Floors Constructed with Prefabricated Wood I-Joists for Compliance with the International Residential Code was developed on the basis of the results of fire tests that met the stringent criteria established by the International Code Council Evaluation Service (ICC-ES) Acceptance Criteria for Prefabricated Wood I-Joists, AC14.
The report was developed to inform interested parties of the multiple options for fire-resistant I-joist floor systems under the IRC. "System Report SR-405 can be used by the authority having jurisdiction, designers, specifiers, and builders, in the design, construction, and approval of wood I-joist fire-protective floor systems that are compliant with Section R501.3 requirements," said Dr. Borjen Yeh, P.E., technical services director for APA. "SR-405 provides easy-to-apply solutions for code compliance, while affording additional fire protection to occupants and firefighters, as required by some local jurisdictions in this country."
Free PDF Download: APA System Report SR-405: Fire Protection of Floors Constructed with Prefabricated Wood I-Joists for Compliance with the International Residential Code.
Webinar: Fire Protective Membranes for Lightweight Floors
Both the 2012 and 2015 versions of the International Residential Code (IRC) include fire protective membrane requirements to enhance the fire performance of residential floor systems. This previously recorded webinar discusses several options that satisfy fire-protective membrane requirements of the IRC related to I-joist floor systems.
APA is a preferred provider for ICC, and 0.10 credits are available for those who view the webinar through the ICC under course name Fire Protective Membranes for Lightweight Floors, ICC course number 2316. Click the "Get Credit" button that appears beneath the video playback screen at the conclusion of the webinar for submitting and obtaining ICC credits and downloading a Certificate of Completion.
The webinar covers options including:
- Gypsum board ceiling membranes
- Gypsum board applied directly to I-joist flanges and webs
- Ceramic fiber blanket
- Mineral wool insulation
- Fire protective coatings
Originally presented on March 10, 2015. Running time approximately 26 minutes.
Webinar Participant Questions and Answers
In the case of field-applied fire protective paints, the same requirements for field-applied fire coatings apply, including the ASTM E119 fire test demonstrating equivalence to 2x10 dimension lumber or structural composite lumber.
Mineral wool insulation is commonly available in most metropolitan areas. Contact material suppliers or distributors that handle the product for costs.
I-joist web holes should be cut prior to the installation of the ceramic blanket. Then the blanket can be cut at the web hole location with a utility knife. Either of these steps can be done before or after the I-joists are installed.
Yes, because a fire is unlikely to reach a joist from only one side.
No, the gypsum membrane covering I-joists is not required to be finished with tape and joint compound for equivalent performance to nominal 2 x 10 lumber floors. In the same way, joints between 5/8-inch wood structural panel membranes are not required to be taped and finished.
If the suspended ceiling system is fire-rated as equivalent to the fire performance of 1/2-inch gypsum on the underside of the I-joist framing, it is considered an alternative to the fire protection requirements in accordance with the first paragraph in the 2015 IRC Section R302.13 and 2012 IRC Section R501.3.
No, APA does not work with any manufacturers of field-applied coatings. However, individual I-joist manufacturers themselves may have such relationships. I-joists coated with an approved field-applied coating are required to demonstrate the same equivalency to 2 x 10 dimension lumber or structural composite lumber as the fire protective membrane methods published in APA System Report SR-405, in addition to several other requirements, such as the effects, if any, of the coating on the structural properties of the I-joists. APA suggests contacting both the coating manufacturer and the I-joist manufacturers that recommend such applications for product approvals.
This question has been addressed by the International Code Council (ICC) and some states. The ICC issued a written interpretation indicating that:
Exception 4 permits floor framing of sawn lumber or structural composite lumber equal to or greater than 2 x 10 nominal dimension to be exempted from the application of the protective membrane to the underside of the floor framing members. The basis for this exception is that tests conducted on floor framing constructed of 2 x 10 lumber and loaded to 50 percent of full design load showed that the assemblies provided adequate time for occupants’ self-evacuation and safety for firefighters performing search and rescue. Floor assemblies using wood trusses may be approved for exemption if the floor assembly demonstrates equivalent fire performance.
Therefore, in order to apply this exemption to floor trusses, the trusses must be tested and evaluated for equivalency to the fire performance of nominal 2 x 10 lumber. This interpretation is consistent with the ruling by several states, such as the Ohio Board of Building Standards (BBS) and Massachusetts Board of Building Regulations and Standards (BBRS). Those rulings are available from the states' respective web sites.
As reported by the American Wood Council (AWC), fire testing with an 80-square-foot unprotected area showed that, for a fire occurring under a protected area, fire blocking provides a minimal level of performance of the membrane system. The 80-square-foot allowance in the 2015 IRC Section R302.13 and 2012 IRC Section R501.3 is intended for passage of multiple HVAC or plumbing through floor penetrations, provided the aggregate area of the penetrations does not exceed 80 square feet per story and fire blocking is installed in accordance with Section R302.11.1 along the perimeter of the unprotected portion, separating the unprotected portion from the remainder of the floor assembly.
See Table R702.3.5 of the 2015 or 2012 IRC.
Based on an engineering analysis in accordance with the 2015 IRC Section 702.3.5, 1 x 4 (nominal) wood furring strips can be installed perpendicular to the bottom flange of I-joists at 16 inches on center, provided that the gypsum boards are directly attached to the furring strips using 1-1/4-inch (32 mm) Type W drywall screws at 12 inches (305 mm) on center. This provides the same number of fasteners with the same fastener penetration depth into the framing as gypsum directly attached to the I-joist flange, and is in compliance with the 2015 IRC Table R702.3.5.
Yes, but FP-02 requires only the I-joist web to be protected.
Refer to APA System Report SR-405 for specific requirements and exceptions.
Yes. In a March 2015 E-Memo released by the Massachusetts Department of Public Safety, the I-joist fire protective membrane methods published in APA System Report SR-405 are specifically recognized as compliant with the BBRS Official Interpretation (No. 2014_03) when used in conjunction with an APA Product Report or ICC-ES Evaluation Report to signify compliance with the Massachusetts code.
This comment gets to the intent of the IRC code requirement. These requirements are intended to increase the fire safety for occupants and firefighters in lightweight residential floors. Yes, the solutions add costs to varying degrees, but they also add benefits—the primary benefit being the increased fire performance of the floor assembly.