Blocking refers to short pieces of lumber installed between studs, joists, or rafters to provide additional structural stiffness, create nailing surfaces for finishes, or interrupt open cavities for fire safety purposes, serving several distinct but related functions depending on where and why it’s installed.
Because blocking serves multiple purposes across different parts of a structure, the specific type and placement varies considerably depending on the particular need being addressed.
A single framed wall or floor might include several different types of blocking, each addressing a distinct structural or safety consideration within the same overall assembly.
What Types of Blocking Are There?
- Fire blocking, interrupting concealed cavities
- Blocking between floor joists for stiffness
- Backing blocks providing nailing surfaces for fixtures
- Blocking at wall intersections for drywall support
Why Is Blocking Important?
Beyond its structural stiffening role, blocking often serves a critical fire safety function, breaking up open cavities that would otherwise allow fire and smoke to spread quickly through hidden spaces within walls and floors. This safety consideration is why building codes specifically require fire blocking at particular locations regardless of whether structural blocking is also needed there.
Blocking also frequently provides the solid backing needed to securely mount fixtures like grab bars, cabinets, or heavy wall-mounted televisions, details that are much easier to plan for during framing than to retrofit later into finished walls. Planning for these needs during framing, rather than as an afterthought, saves considerable effort during later finishing stages. This forward planning saves both time and cost later in the project. This planning saves time down the road.
Blocking vs. Fire Blocking
Blocking is the general term covering multiple purposes, including stiffness and nailing surfaces. Fire blocking is one specific application of blocking, required by code at particular locations specifically to interrupt fire and smoke spread through concealed cavities.