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The Code Authority Q&A: Fireblocking

Fireblocking is an approved material used to protect against fire spread in combustible concealed spaces.

Flames on a black background

November 29, 2023

Questions and answers

Q: What is fireblocking?

A: It is a building material or a material approved by the code official or code authority that is required by the building code to protect against fire spread in combustible concealed spaces.

Q: Why is fireblocking required?

A: Section 718 of the 2021 edition of the International Building Code (IBC) and Section R302.11 of the 2021 International Residential Code (IRC) address requirements for concealed combustible spaces. Both codes require prescriptive fireblocking to ensure that concealed spaces are not continuous.

Q: Where is fireblocking required?

A: Fireblocking is required within concealed spaces of buildings that use wood frame construction to protect against fire spread in the following locations:

  • The intersections of a wall and floor or ceiling
  • Interconnections between concealed vertical and horizontal spaces such as occur at soffits, drop ceilings and cove ceilings
  • The top and bottom of a stair stringers, within the concealed space at the top and the bottom of the run
  • Openings around vents, pipes, ducts, cables and wires at ceiling and floor level, with an approved material to resist the free passage of flame and products of combustion 

Q: What if the wall has double or offset studs?

A: Walls constructed using parallel rows of studs or staggered studs are required to have fireblocking installed.

Q: What materials can be used for fireblocking?

A: The building code allows a wide variety of materials to be utilized as fireblocking. Among them are common building materials such as half-inch gypsum panels, lumber, cement board and both mineral wool and glass fiber insulation. The dimensions and properties of each of these are specified in the building code.  

Fireblocking materials  
2X Lumber 1 layer
1X Lumber 2 layers
Plywood 23/32 inch
Particleboard 3/4 inch
Cement millboard 1/4 inch
Batts and blankets Mineral wool
  Mineral fiber
  Unfaced fiberglass

Q: How is fireblocking installed?

A: Although the building code does not prescribe how to install these materials specifically, it does require that the integrity of the fireblock materials be maintained.

Q: Is fireblocking different from firestopping?

A: Fireblocking is different from firestopping. Fireblocking is the installation of additional approved building materials that help slow fire progression in combustible construction.

Firestopping is a listed (certified) system installed to protect penetrations into or through a fire-resistance-rated assembly. Firestopping requires testing in accordance with UL 1479, the Standard for Fire Tests of Penetration Firestops, or ASTM E814 to maintain the fire resistance rating of the assembly.


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