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Fireblocking vs draftstopping: what it means on an inspection

Rafter Tie editorial teamUpdated 3 min read

Fireblocking is material that closes hidden spaces in walls, soffits and stairs so fire and hot gases cannot travel through them unchecked. Draftstopping divides large, open floor-ceiling or attic cavities into smaller areas so air and fire cannot run the whole length. Fireblocking closes small spaces, and draftstopping subdivides big ones.

Two drawings side by side: a stud wall with short blocks closing the stud cavities, labeled fireblocking, and a long floor-ceiling cavity divided by a vertical barrier, labeled draftstopping
Fireblocking closes a cavity. Draftstopping cuts a long one into smaller areas.
Use this diagram

How to tell which one you are looking at

  1. Look at the cavity. A narrow concealed space such as a stud bay, a soffit, a furred wall or the space beside a stair stringer calls for fireblocking. A wide open concealed space, such as the cavity between a floor and the ceiling below it in a large area, calls for draftstopping.
  2. Look at where fireblocking goes. Typical locations are the top and bottom of stud walls at ceiling and floor levels, at set intervals along tall walls, in soffits and drop ceilings, at the top and bottom of stair stringers, and around pipes, vents and ducts where they pass through floors and ceilings. The section lists them all; read it for your edition.
  3. Look at the material. The code lists the allowed fireblocking materials. Solid lumber of a minimum thickness is a familiar one, and the list also names sheet materials and others. Ordinary insulation is not automatically fireblocking; only the materials the code lists, installed the way it says, count.
  4. Look at where draftstopping goes. It divides floor-ceiling assemblies where there is usable space both above and below the cavity, and the section lists the other conditions and sets an area limit for each section of cavity.
  5. Check penetrations. A hole through a fireblock or draftstop for a pipe or wire must be sealed with an approved material. An open hole defeats the block.

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Public Safety and Special Construction

In a new bedroom, the only emergency escape window has a keyed sash lock, with the key hanging on a hook beside the window. What should the inspector do?

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Common mix-ups

  • Fireblocking versus firestopping. Firestopping is the sealing of a penetration through a fire-rated assembly with a listed system. Fireblocking is a general barrier in a concealed space. The words are close and the rules are separate.
  • Draftstopping versus fireblocking in a stud wall. In a stud wall the question is fireblocking. Draftstopping is about large horizontal cavities.
  • Both are not the same as a fire-resistance rating. Fire-rated walls and floors are a separate subject with their own assemblies.

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Fireblocking and draftstopping on the B1

Fireblocking is listed under wall construction, which is 27% of the B1, and the fire protection provisions are in Chapter 3. The two terms are easy to swap, so the exam favors questions that give a location and ask which one applies. Find both by name in your table of contents, tab them side by side and confirm the section numbers in your edition, since some Chapter 3 numbers changed in 2024.

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Train the lookup with the code navigation drill. Then read band joist and cripple wall, which both create concealed spaces at the floor line, and return to the IRC terms glossary for the next term.

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