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Missing Fire Blocking

Many multi-level houses have small sections of floor that are balloon-framed into adjoining walls. The framing in Figure 3 is typical, and shows good support for the joists where they meet the tall stud wall.



Figure 3.

The missing fire blocking and edge blocking in this photo can easily be installed at the top and bottom of joists in the bays without ductwork (top illustration). Where ducts get in the way, install a metal collar, which will choke off a fire and prevent it from spreading into the wall. Where soffits above kitchen wall cabinets are framed before drywall is installed (lower illustration), the joint between the wall and ceiling also needs fire blocking. The problem, however, is that the fire blocking is missing where the horizontal floor meets the vertical wall. Without blocking, flames in the lower area can migrate to upper stories through the open bay where the joists meet the wall. Solid blocking is also necessary to provide lateral support when balloon-framed studs are taller than 10 feet. The solution in this case is complicated by the ductwork. It's easy enough to add fire blocking at the bottom of the joists, and to add blocking along the unsupported edge of the subfloor. There isn't enough room, however, to add blocking at the top of the joists in the bays that carry the ductwork. In this case, I asked the builder to fabricate a metal collar that would surround the ductwork. Even without sealants, this collar closes off the air flow enough to reduce the ability of a fire to sustain itself in these stud bays. Another common area where fire blocking is omitted is in soffits built above kitchen wall cabinets. If the ceiling and wall are drywalled before the soffit is framed, then the drywall serves as a firestop. When the soffit is framed first, however, you need to install solid blocking where the ceiling of the soffit meets the wall.