Fire Ratings for CMU

Fire Ratings for CMU

The fire resistance of concrete block can be determined in one of three ways: Full scale testing, Rating services such as “UL” or Calculation. The calculation method is the most practical and most commonly used. The calculation method conforms to the parameters established in ACI 216.1-97 / TMS 0216.1-97 and is included in the International Building Code (IBC) as a reference standard.
The calculation method utilized in the Masonry Code, determines fire resistance ratings based on the equivalent thickness of the concrete masonry unit and the aggregate type used in the manufacturing process.

Filling the core of the blocks with non-combustible materials such as sand, Vermiculite or grout can increase the rating values. Ratings can also be increased by adding plaster or gypsum wallboard to the wall face.

Typical Equivalent Thickness for Block: (Based on NCMA TEK #7-1A)

4” hollow	2.7"
4” Solid -	3.6"
6” hollow -	3.1"
8” hollow	4.0"
10” hollow	5.0"
12” hollow	5.7"

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For a complete review of the information available on fire resistance for concrete masonry, go to ncma.org, click on the TEK Note button, select Missouri, and choose from either Midwest Block & Brick or Kirchner Block & Brick.