How AWC & NAHB Created a Competitive Advantage for 2x10s Through the Code

Originally published by: SBCRI-SBCA Investigative Report #2October 15, 2015

The following article was produced and published by the source linked to above, who is solely responsible for its content. SBC Magazine is publishing this story to raise awareness of information publicly available online and does not verify the accuracy of the author’s claims. As a consequence, SBC cannot vouch for the validity of any facts, claims or opinions made in the article.

Editor's Note: The following is an updated summary version of an SBC Industry News article that ran March 16, 2015 entitled “SBCA’s Views on Creating Fair Code Policy”. The role of AWC and NAHB in the creation and adoption of R501.3 (IRC-12) is defined in the article entitled, “How Floor Trusses Became an Endangered Species, the Politics of it All”.

SBC Industry News has shared a series of news items related to International Residential Code (IRC) R501.3 (adopted by Ohio as R502.14) that reflect on an IRC code change that effectively bans the use of trusses and I-joists from residential markets that have basements. This article provides information about the requirement for a ½" gypsum wallboard membrane to be applied to everything except 2x10 floor joists. This requirement became part of the 2012 and 2015 IRC and has been adopted into law by a few states. It is clear this code change has altered the free market to favor 2x10s and alternatives tested in a non-standardized manner. Other “normally used” structural floor members are now more expensive because of the application of a ½" gypsum wallboard membrane. This is important news from a public policy point of view, so we have included links to related news items.

SBCA believes the following observations are true and form the basis for a more fair and equitable code policy:

  • The structural framework of a building does not cause a fire.
  • The contents of a building catch fire and, in general, building contents differ from structure to structure. It is impossible for the fire service to know what the contents are in advance of a fire. As a consequence, all fires are different and all fire ground activities are challenging work environments that are unique in evolution and prosecution.
  • Working smoke detectors are the best way to save lives. Smoke detectors effectively alert and compel people to leave a building during a fire, thus mitigating the risk of life loss. SBCA believes a primary public policy should be to require hard-wired smoke detectors. The fire service is best protected if they do not have to go into a burning building to save a life. The fire ground decisions then focus on saving property, and no property is worth a firefighter death.
  • The next best way to save lives is by applying a 1/2-inch regular gypsum wallboard membrane to all unprotected structural members in locations where the building code currently allows this. In other words, change R501.3 to read as follows:

R501.3 Fire protection of floors. 

Floor assemblies, not required elsewhere in this code to be fire-resistance rated, shall be provided with a 1/2-inch (12.7 mm) gypsum wallboard membrane, 5/8-inch (16 mm) wood structural panel membrane, or equivalent on the underside of the floor framing member. 


  1. Floor assemblies located directly over a space protected by an automatic sprinkler system in accordance with Section P2904, NFPA13D, or other approved equivalent sprinkler system.
  2. Floor assemblies located directly over a crawl space not intended for storage or fuel-fired appliances.
  3. Portions of floor assemblies can be unprotected when complying with the following:

3.1. The aggregate area of the unprotected portions shall not exceed 80 square feet per story

3.2. Fire blocking in accordance with Section R302.11.1 shall be installed along the perimeter of the unprotected portion to separate the unprotected portion from the remainder of the floor assembly.

  1. Wood floor assemblies using dimension lumber or structural composite lumber equal to or greater than 2-inch by 10-inch (50.8 mm by 254 mm) nominal dimension, or other approved floor assemblies demonstrating equivalent fire performance.
  • Beyond a sound smoke detector or single-membrane policy, the next best way to save lives is automatic sprinklers. One way to ensure sprinkler applications are low cost and always functioning is to do as fire service educator Frank Brannigan suggested: Allow sprinkler systems to be installed by regular residential plumbers, integrated and serial with the plumbing of all toilets in the building. If the toilet is working the sprinklers are assured to be working and if there is a leak it will assuredly be fixed.

SBCA has consistently provided public policy and code change proposals based on a fair assessment of the facts available to us. As President John Adams said ('Argument in Defense of the Soldiers in the Boston Massacre Trials,' December 1770), “Facts are stubborn things; and whatever may be our wishes, our inclinations, or the dictates of our passion, they cannot alter the state of facts and evidence.”

Related Articles: