Answering the Question: What Is Equivalent Protection to a 1/2-inch Gypsum Wallboard Membrane?

Background:

R501.3 (IRC-12) or R302.13 (IRC-15) states the following – “Floor assemblies….shall be provided with a 1/2-inch (12.7 mm) gypsum wallboard membrane…… or equivalent…….

Question:

What does “or equivalent” to a 1/2-inch (12.7 mm) gypsum wallboard membrane really mean?

Underwriters Laboratory (UL) provides objective perspective on page 65 of it’s report entitled, “Improving Fire Safety by Understanding the Performance of Engineered Floor Systems and Providing the Fire Service with Information for Tactical Decision Making (“UL Report”), they provide the following counsel with respect to the wording of equivalence (i.e. …..or equivalent on the underside of the floor framing member…..) as referenced above:

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What change does the UL Report recommend be made to R501.3 or R302.13?

To ensure that the statement “Floor assemblies….shall be provided with a 1/2-inch (12.7 mm) gypsum wallboard membrane…… or equivalent…….” is easy to understand and implement, UL’s counsel would be to change the first paragraph of R501.3 or R302.13 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 where equivalent is defined as fire endurance performance of 26 minutes using ASTM E119 standard fire endurance testing with a superimposed load simulating a maximum load condition (i.e. 100% design load) or as defined by the time assigned to wallboard membranes from IBC Table 722.6.2(1).

How does the UL Report’s recommended change affect R501.3 or R302.13 overall?

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 where equivalent is defined as fire endurance performance of 26 minutes using ASTM E119 standard fire endurance testing with a superimposed load simulating a maximum load condition (i.e. 100% design load) or as defined by the time assigned to wallboard membranes from IBC Table 722.6.2(1).

Exceptions: 

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.

4. 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.

What testing supports the elimination of “Exception 4” of R501.3 or R302.13?

All unprotected testing yields fire endurance performance that is far less than what is required in R501.3 -- “Floor assemblies….shall be provided with a 1/2-inch (12.7 mm) gypsum wallboard membrane…… or equivalent…….”. 26 minutes of fire endurance performance is a very long time in an ASTM E119 test as shown by the following table:

Testing behind the UL Report found unprotected 2x10 floor assembly performance was 7:04 minutes when tested under full design load ASTM E119 standardized conditions. It is important to note that UL followed the complete ASTM standard testing protocol. Page 24 of the UL Report provides details of the benchmark testing and comparisons made.

UL states definitively that it is important to protect “all types of flooring systems, including dimensional lumber.”

  • UL echoes the intent of the law on page 3 of their test report, stating, “The main objective of this study was to improve firefighter safety by increasing the level of knowledge on the response of residential flooring systems to fire. Several types (or series) of experiments were conducted and analyzed to expand the body of knowledge on the impact of fire on residential flooring systems.”
  • UL concludes on page 66 of their test report that basement floor assembly fires are a challenge to the fire service where, “This [the fire service response time scenario] assumes that the fire is witnessed, called into the fire department, the fire department is dispatched, the fire department arrives and the fire department begins their firefighting operation in 8 minutes. While possible, this is not the case for the majority of fires that occur across the United States. This emphasizes the importance of protecting all types of flooring systems, including dimensional lumber.” (emphasis added.)
  • UL states on page 67 of their test report, “There are little if any warning signs of collapse so it is very important to understand the hazards associated with a basement fire because the consequences of falling through a floor into a basement fire are pinnacle.”
  • UL concludes on page 69 of their test report, “This research study provides data to substantiate the need to protect dimensional lumber floor systems to improve firefighter safety.” (emphasis added.)

The Structural Building Components Association (SBCA) confirmed the UL testing results through testing at NGC Testing Services (NGC), an International Accreditation Service (ICC-IAS) accredited ISO/IEC 17025 ASTM E119 fire testing facility. SBCA chose to test at NGC versus UL so the SBCA ASTM E119 test procedure and resulting test data would be an independent assessment of floor assembly performance. SBCA testing found unprotected 2x10 floor assembly performance was 10:35 minutes. This result confirms the UL testing result. (see table above).

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