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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 FLOOR112soffit / dropped ceiling3stair stringer445pipe/duct/ventREQUIRED LOCATIONS — §R302.111
Concealed stud walls at ceiling and floor levels (plate lines)
2
Concealed walls/furring at 10 ft max horizontal intervals
3
Connections between horizontal (soffit, drop ceiling, cove) and vertical concealed spaces
4
Concealed spaces between stair stringers, top and bottom of the run
5
Openings around vents, pipes, ducts, cables, wires at ceiling/floor level — approved material
ACCEPTED MATERIALS — §R302.11.12× nominal lumber · two layers of 1× lumber23/32" wood structural panel (joints backed)½" gypsum board · ¼" cement boardBatts/blankets of mineral or glass fiber, securedDRAFTSTOPPING (§R302.12):subdivide open floor assemblies > 1,000 sfNOTE · IRC 2021 §R302.11Fireblocking cuts off concealed draft openings — it is an inspection checklist item at frame stage (see the Single-Family Addition checklist)NOT TO SCALE
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.
Sections cite the 2021 International Residential Code and 2023 National Electrical Code as model standards. This is BuildSpec’s own summary — not ICC or NFPA text; read the authoritative language at codes.iccsafe.org. Your state may be on a different edition with amendments — check your jurisdiction page or get an Address Report.
Deck Footings →Deck Ledger →GFCI Protection →Egress Windows →Stairs →Handrails & Guards →