In combustible construction, fireblocking shall be provided to cut off both vertical and horizontal concealed draft openings and to form an effective fire barrier between stories, and between a top story and the roof space.
Fireblocking shall be provided in wood-framed construction in the following locations:
In concealed spaces of stud walls and partitions, including furred spaces and parallel rows of studs or staggered studs, as follows:
- 1.1. Vertically at the ceiling and floor levels.
- 1.2. Horizontally at intervals not exceeding 10 feet (3048 mm).
- At interconnections between concealed vertical and horizontal spaces such as occur at soffits, drop ceilings and cove ceilings.
- In concealed spaces between stair stringers at the top and bottom of the run. Enclosed spaces under stairs shall comply with Section R302.7.
- At openings around vents, pipes, ducts, cables and wires at ceiling and floor level, with an approved material to resist the free passage of flame and products of combustion. The material filling this annular space shall not be required to meet the ASTM E136 requirements.
- For the fireblocking of chimneys and fireplaces, see Section R1003.19.
- Fireblocking of cornices of a two-family dwelling is required at the line of dwelling unit separation.
Except as provided in Section R302.11, Item 4, fireblocking shall consist of the following materials.
- Two-inch (51 mm) nominal lumber.
- Two thicknesses of 1-inch (25.4 mm) nominal lumber with broken lap joints.
- One thickness of 23/32-inch (18.3 mm) wood structural panels with joints backed by 23/32-inch (18.3 mm) wood structural panels.
- One thickness of 3/4-inch (19.1 mm) particleboard with joints backed by 3/4-inch (19.1 mm) particleboard.
- One-half-inch (12.7 mm) gypsum board.
- One-quarter-inch (6.4 mm) cement-based millboard.
- Batts or blankets of mineral wool or glass fiber or other approved materials installed in such a manner as to be securely retained in place.
- Cellulose insulation installed as tested in accordance with ASTM E119 or UL 263, for the specific application.
Batts or blankets of mineral or glass fiber or other approved nonrigid materials shall be permitted for compliance with the 10-foot (3048 mm) horizontal fireblocking in walls constructed using parallel rows of studs or staggered studs.
Unfaced fiberglass batt insulation used as fireblocking shall fill the entire cross section of the wall cavity to a height of not less than 16 inches (406 mm) measured vertically. Where piping, conduit or similar obstructions are encountered, the insulation shall be packed tightly around the obstruction.
Loose-fill insulation material shall not be used as a fireblock unless specifically tested in the form and manner intended for use to demonstrate its ability to remain in place and to retard the spread of fire and hot gases.
The integrity of fireblocks shall be maintained.