Fireblocking

Purpose and locationsR302.11#

Fireblocking is required to cut off concealed draft openings (vertical and horizontal) and form an effective barrier between stories and between a top story and the roof space.

• In concealed stud wall spaces at the ceiling and floor levels, and at 10 foot intervals vertically and horizontally
• At interconnections between concealed vertical and horizontal spaces such as soffits, drop ceilings, and cove ceilings
• In stair stringers at the top and bottom of each run
• At openings around vents, pipes, ducts, cables, and wires at ceiling and floor levels
• At the top and bottom of a chimney chase and around fireplaces

Acceptable materialsR302.11.1#

Fireblocking materials must resist the free passage of flame and products of combustion. Typical accepted materials include 2 inch nominal lumber, two layers of 1 inch nominal lumber with broken lap joints, 23/32 inch wood structural panels with joints backed by the same, 3/4 inch particleboard with backed joints, 1/2 inch gypsum board, 1/4 inch cement-based millboard, batts or blankets of mineral wool or fiberglass secured in place, and cellulose insulation installed as tested.

PenetrationsR302.11.2#

Openings around vents, pipes, ducts, cables, and wires that penetrate a ceiling or floor assembly must be sealed with an approved material to resist the free passage of flame and products of combustion. Unfaced batt insulation stuffed into a pipe penetration is not a substitute for an approved sealant or fireblock.

Unfaced fiberglass as fireblockingR302.11.1#

Loose-fill or batt fiberglass is acceptable as fireblocking only when used to fill the entire cross section of the stud or joist bay and secured so that it cannot be pulled or blown out. A partial stuff at the top plate does not meet the requirement.

Common inspection flags#

Typical fireblocking failures flagged at rough-in and insulation inspection:

• Soffit above kitchen cabinets open to the stud bay behind
• Plumbing chase from basement to attic with no blocking at the floor plate
• Stair stringer pockets left open under the landing
• Recessed light housings and bath fan boots with gaps left unsealed at the top plate
• Dropped ceiling in a laundry with no vertical-to-horizontal cutoff at the wall