Where fireblocking goes
Under IBC 718.2.2, concealed wall spaces, including furred spaces and parallel or staggered stud rows, are fireblocked in two directions:
- Vertically at the ceiling and floor levels.
- Horizontally at intervals not exceeding 10 ft (3048 mm).
The horizontal figure is 10 ft. The 8 ft, 12 ft and 20 ft intervals are not the code figure.
Approved lumber
IBC 718.2.1 allows:
- 2 in nominal lumber, or
- two thicknesses of 1 in nominal lumber with broken lap joints.
A single layer of 1 in nominal lumber is a draftstopping material, not fireblocking. Two 1 in layers with aligned joints fail because the joints must be broken lap. A single 1½ in nominal layer is less than the 2 in nominal required.
Approved panels
IBC 718.2.1 lists one thickness of 0.719 in (23/32 in, 18.3 mm) wood structural panel with joints backed by 0.719 in panels. Both parts are required:
- A 23/32 in panel with unbacked joints misses the backing requirement, a listed common error.
- A 3/8 in panel is the draftstopping minimum. Mixing up 23/32 in and 3/8 in is a listed common error.
- A 1/2 in wood structural panel is thinner than the 0.719 in required. The 1/2 in figure belongs to gypsum board, which is an approved fireblocking material.
Fireblocking versus draftstopping
The trap in this area is swapping the two material lists. Fireblocking asks for the heavier material: 2 in lumber, not 1 in; 23/32 in panels with backed joints, not 3/8 in. When a figure looks like the smaller one, check whether it is the draftstopping minimum.