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Home / Code Guides / Fireblocking

Fireblocking Code — Where It Goes and What Materials Qualify

Fireblocking is the cheapest fire protection in the house and the most commonly missed inspection item. The concept: cut every concealed channel that would let fire travel between floors or across a ceiling.

FIREBLOCKING LOCATIONS — WALL SECTIOND262ND FLOOR1ST FLOOR11210 ft MAXintervalsoffit / dropped ceiling3stair stringer445pipe, duct or ventREQUIRED LOCATIONS — §R302.111Concealed stud walls and partitions, verticallyat the ceiling and floor levels2Concealed stud walls and partitions,horizontally at intervals not exceeding 10 ft3Connections between concealed vertical andhorizontal spaces: soffits, drop ceilings andcove ceilings4Concealed spaces between stair stringers, at thetop and bottom of the run5Openings around vents, pipes, ducts, cables andwires at ceiling and floor level, with anapproved materialACCEPTED MATERIALS — §R302.11.12" nominal lumberTwo thicknesses of 1" nominal lumber, broken lap joints23/32" wood structural panel, joints backed3/4" particleboard, joints backed½" gypsum board¼" cement-based millboardBatts or blankets of mineral wool or glass fiberCellulose insulation, installed as testedNot to scale. The 10 ft limit is a maximum spacing.Fireblocking cuts off concealed draft openings and forms a barrier between stories and between the top story and the roofspace (§R302.11).FIREBLOCKING · IRC 2021 §R302.11 · §R302.11.1
Fireblocking locations and materials — IRC 2021 R302.11.Open full diagram →
RequirementModel Code StandardSection
Wall spacesConcealed stud walls and furred spaces blocked at ceiling and floor levels, and at 10 ft intervals horizontallyIRC R302.11
Vertical-to-horizontal connectionsBlocked at interconnections between vertical wall cavities and horizontal spaces — soffits, drop ceilings, cove ceilingsIRC R302.11
StairsBlocked in concealed spaces between stair stringers at the top and bottom of the runIRC R302.11
PenetrationsOpenings around vents, pipes, ducts, cables and wires at ceiling and floor level sealed with an approved material resisting fire and combustion productsIRC R302.11
Approved materials2x nominal lumber, 23/32 in. wood structural panel, 1/2 in. gypsum board, mineral wool or fiberglass batts securely retained, and unfaced fiberglass at least 16 in. high for 10-ft blockingIRC R302.11.1
Chimneys & fireplacesSpaces between chimneys and floors/ceilings blocked with noncombustible materialIRC R1003.19

Worth knowing

  • Fireblocking is not draftstopping — draftstopping subdivides big concealed floor spaces (R302.12); fireblocking cuts the channels. Inspectors check both.
  • Canned spray foam qualifies only if it is a listed fireblock foam — ordinary gap-and-crack foam is not an approved fireblocking material.
  • The basement remodel classics: open stud bays behind a new furred wall, and the soffit over the kitchen cabinets connecting to a wall cavity.
  • Take photos before drywall. Fireblocking is invisible at final and re-opening walls is the expensive way to prove it.

Common questions

What does the code say about wall spaces for Fireblocking?

Concealed stud walls and furred spaces blocked at ceiling and floor levels, and at 10 ft intervals horizontally. (IRC R302.11)

What does the code say about vertical-to-horizontal connections for Fireblocking?

Blocked at interconnections between vertical wall cavities and horizontal spaces — soffits, drop ceilings, cove ceilings. (IRC R302.11)

What does the code say about stairs for Fireblocking?

Blocked in concealed spaces between stair stringers at the top and bottom of the run. (IRC R302.11)

Adopted edition by state

Base-code year from BuildSpec’s adoption records. States often amend the base code, and your city or county may differ, so confirm with your building department.

Related sections and guides

This guide is BuildSpec’s own summary, not code text. It cites the 2021 International Residential Code and the 2023 National Electrical Code as model standards. The IRC 2021 text itself is in the Code Library for signed-in members; BuildSpec publishes no NEC text, which is at nfpa.org.Neither is an adoption record: your state may be on a different edition with amendments — check your jurisdiction page or get an Address Report.
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