Whole-House Fire Blocking

DROP-IN TUBS

If the wall behind a drop-in bathtub is finished, no blocking is required. If the wall isn’t finished, install 2-by material between the studs, flush with the top of the tub. Insulation batting in the wall extending at least 16 in. above the tub is also sufficient.

BASEMENT WALLS

The gap behind a 2x4 wall has to be sealed off from the joist bays above the wall.

LANDING

Install blocking in stud cavities above a landing over an unfinished space.

SOFFIT WITH A FINISHED BACK

If the wall and ceiling were drywalled before the soffit was put in, no further fire blocking is needed.

SOFFITS

Soffits provide an easy path to floor and ceiling joist bays if they’re not fire blocked. Without a soffit, the top plate provides the fire blocking.

SOFFIT WITH AN UNFINISHED BACK

Block off the stud bays at the base of the soffit with 2-by material. Or install 2-by blocking or approved sheathing along the back of the soffit.

STRINGERS

Install 2-by blocking between stair stringers to prevent fire from entering the joist bays. Cover the underside of stair stringers with drywall.

STAIRS ABOVE UNFINISHED SPACE

Angle-cut 2-by fire blocking to fit between the studs on the outside of the stair stringers.

PLUMBING AND ELECTRICAL

Where plumbing pipes or electric cables pass through wall plates, fill any resulting gaps with an approved fire-blocking material.

CONCEALED SPACES

A dropped ceiling needs fire blocking where the joists meet the wall.

FLOOR JOISTS

If ceiling finish material is attached directly to the joists, no further draft stopping is necessary, as the joist bays are likely less than 1,000 sq. ft.

TRUSS-STYLE JOISTS

If ceiling finish material is applied to truss-style joists, apply draft-stopping material to cover only enough trusses to limit unfinished concealed spaces to less than 1,000 sq. ft.

DROPPED CEILING

Install draft-stopping material to limit unfinished concealed spaces to less than 1,000 sq. ft.`