How Floor Trusses Became an Endangered Species, the Politics of it All

Editor’s Note: SBC Industry News has recently shared a series of firefighter-related news items that has made us reflect on the IRC code change proposal effectively altering the competitive landscape with respect to the use of trusses and I-joists in residential markets where basements are standard. The news items contained in this SBC Industry News-Special Edition! provide a retrospective on the facts surrounding the need for a ½ inch gypsum wallboard membrane to be applied to everything but 2x10 floor joists that became part of the 2012 International Rsidential Code (IRC). It is clear this code change has altered the free market to favor 2x10s, where all other structural floor member alternatives now have to add a gypsum ceiling and are therefore more expensive. This is important news from a public policy point of view so we have included hyperlinks to other recent, related news items, which can be found at the bottom of the page.

Here’s a quick history lesson. In reviewing public documents surrounding the 2010 Final Action Hearing of the ICC with regard to proposals RB31-9/10 and RB87-9/10, one would gather the following information:

The American Wood Council (AWC) on behalf of solid wood and wood structural panel products; APA-The Engineered Wood Association (APA) on behalf of wood structural panel products, I-joists and composite structural lumber; and, the National Association of Homebuilders (NAHB) on behalf of builders, have submitted many building code proposals throughout the years advocating for their best interests.

By May 2010, AWC (a subsidiary of the American Forest & Paper Association (AF&PA)) and NAHB were in negotiations to advocate their interests. The original code change proposal was AWC’s RB31-9/10; the negotiated code change proposal was RB87-9/10. Their collaborative proposal amended Section R501.3 of the 2012 IRC/IBC (see box at right) to mandate the application of ½ inch gypsum to floor assemblies, unless a sprinkler system is installed or the joists are made from solid-sawn lumber.

Damaging Code Provision

It’s important to note that SBCA was not part of this group, nor was SBCA privy to the private discussions regarding this proposal that were said to be facilitated by AWC at NAHB’s headquarters. A quick look at the membership and mission of AWC (AF&PA) and NAHB gives insight into the agenda of each of these organizations:

  • NAHB does not want sprinklers to be mandated in homes due to the increased cost in time and materials it adds to the construction of a house. By excluding 2x10 solid sawn joists from the gypsum ceiling membrane requirement, builders retain a low-cost option for unprotected floors.
  • The AWC had nothing to lose through this proposal; in fact, its membership was effectively provided a code-mandated floor joist sales advantage in any region of the country that previously allowed unprotected floors, such as floors over basements.
  • The fire service was being asked to participate in a negotiated victory, which was essential for successful IRC passage. It had struggled for years in its push for mandatory sprinklers, fighting the political clout of NAHB and local Home Builder Associations (HBAs). This proposal was a perfect foot in the door toward greater firefighter safety, while having the full support of the homebuilders.

SBCA has continually advocated throughout the code change process that ½ inch regular gypsum (which is equivalent to a 15-minute fire protection membrane rating per IBC Section 722.6.2) should be used across all light-frame floor systems, including 2x10 applications. This is because the directly comparable 100 percent design load fire testing indicated that 2x10s perform similarly to open-web floor trusses (see ASTM E119 table below). Furthermore, if the goal is to truly provide better protection for the fire service during a fire event, protecting everything makes the most sense.

  1. 4-1.4 Report: ASTM E119-73: Fire Endurance Test on a Floor Assembly (Design FC-209) Consisting of 2 x 10 Wood Joists with a 23/32 in. Plywood Deck and Vinyl Tile Flooring. Authors: Factory Mutual Research Sponsor: National Forest Products Association Date: June 20, 1974
  2. 4-1.5 Report: ASTM E119 Fire Endurance Test of a Floor Assembly (Design FC-212) Consisting of 2 x 10 Wood Joists with a 23/32 in. Plywood Deck and Nylon Carpet Flooring. Authors: Factory Mutual Research Sponsor: National Forest Products Association Date: July 17, 1974
  3. 4-1.6 Report: Fire Endurance Test of Unprotected Wood Floor Constructions For Single-Family Residences, NBS 421346. Author: B.C. Son Sponsor: United States Department of Housing and Urban Development Date: May 10, 1971. In two tests, numbers 2 and 4, the 2 x 10 joists were Douglas fir, which was assumed to have a stress level of 1050 psi in bending. The average temperature inside the furnace was measured by 12 protected thermocouples, and followed the ASTM E119-69 time/temperature curve by automatic control of the gas flow to the burners.
  4. 4-1.7 Report: Replicate Fire Endurance Tests on Unprotected Wood Joist Floor Assembly Authors: R.H. White, E.L. Schaffer, and F.E. Woeste Sponsor: Forest Products Laboratory Date: March, 1983 Nominal 2 x 10 Douglas fir dimension lumber, 14 ft. long, was used in the tests. The testing consisted of eleven 14 x 18 ft. unsheathed joist floors. Five floors supported a maximum floor load of 79.2 psf (100% of maximum design load based on fiber bending stress, per the test report). The standard ASTM E119 time/temperature curve was followed for each floor. Gas burners within the furnace provided the standard fire exposure to the test specimen.
  5. 4-1.8 Report: A Floor-Ceiling Assembly Consisting of Wood Trusses with a Plywood Floor. (Design FC-250) Author: Factory Mutual Research Sponsor: Truss Plate Institute Date: May 10, 1977. The floor assembly consisted of 12 in. deep floor trusses, made with nominal 2 x 4 wood chords and webs, spaced 24 in. on center. The trusses were exposed from below. The assembly was subjected to a uniformly distributed live load of 55.1 psf, which resulted in a combined live and dead load of 60 psf. The test was conducted in accordance with ASTM E119-76.
  6. 4-1.9 Report: Floor Assembly Consisting of 7.25 in. Deep Steel Joists with 23/32 in Plywood Deck and Vinyl Tile Flooring. (Design FC-208) Authors: Factory Mutual Research Sponsor: National Forest Products Association Date: June 19, 1974 This test construction consisted of 7.25 in. deep channel-shaped steel joists made of 16 gauge steel spaced 24 in. on center. The tests followed the ASTM E119 standard time/temperature curve as measured by 16 thermocouples, placed 12 in. below the lower flange of the joists.

Winners & Losers through Politics

Given this, why would the building code adopt the provision forwarded by NAHB and AWC?  The simple answer is politics. The general public assumes model building code development is based on serving the public’s best interest by applying the best science available to create the best possible products for safe use in construction, all while meeting the building code’s mission which states:

101.3 Intent. The purpose of this code is to establish the minimum requirements to safeguard the public health, safety and general welfare through structural strength, means of egress facilities, stability, sanitation, adequate light and ventilation, energy conservation, and safety to life and property from fire and other hazards attributed to the built environment and to provide safety to fire fighters and emergency responders during emergency operations.

However, the building code is not a technical document serving this intent; it is actually a political document. We ended up with the R501.3 proposal (see Figure 1) being approved and adopted into the 2012 IRC/IBC because of the strong political relationships that AWC and NAHB have within the ICC, enabling them to convince the committee that light-weight construction is all that needs protection if sprinklers were not used.

SBCA and its members strongly believe in a key engineering and building code principle, which is to provide structural building component solutions that safeguard the public, while also serving the public’s desire to create structures that are affordable and environmentally responsible. As the building code states, this also includes providing “safety to fire fighters during emergency operations.”

However, in the case of this code provision, the fourth exception appears to intentionally make solid-sawn floor joists the clear economic winner against all its engineered product substitutes in the market, steel joists, engineered wood I-joists and floor trusses being the primary products currently used. The mantra appeared to be that while lightweight construction is bad, 2x10s are better. Yet, in looking at the ASTM E119 table, one can see that the actual fire performance of solid-sawn versus floor trusses is very similar (between 6-13 minutes). New ASTM E119 test data affirms that this testing is accurate.

The key problem with the ICC’s code development environment is that the time constraint allows for political (relational) factors to trump other factors. Proponents and opponents of a proposal have only two minutes to explain highly complicated and technical subjects to a committee or an assembly that generally cannot possibly have a deep level of technical expertise on all the topics that make up the building code. It would be unreasonable to expect everyone to know everything. Consequently, the code development process relies upon two minute sound bites from experts like AWC and NAHB. The question remains, are groups like AWC and NAHB experts that serve the best interests of code development, or are they advocates for a given agenda?

In this case, SBCA’s arguments for a sound-science-based code provision that also met the goal, “to provide safety to fire fighters during emergency operations,” were not successful in convincing the committee members to favor our proposal over the AWC/NAHB proposal.

Two Approaches

As local jurisdictions begin to adopt the 2012 IBC/IRC, SBCA has been working with component manufacturers across the country to convince the state/local authorities to take one of the following actions:

  • If fire fighter safety is the core issue, amend the code to require the application of a ½ inch gypsum wallboard membrane onto all unprotected floors assemblies; or,
  • Based on science and fairness, remove exception 4 of Section R501.3, or remove the entire section.

While SBCA believes that adding a 15-minute fire protection membrane to the underside of all unprotected floor joists is the best and fairest approach to providing safety to fire fighters, the added cost of doing so generally becomes problematic as the jurisdiction confronts the local political clout of HBAs.

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