Can You Make a Brace Between Floor Joists?

Types of Joists

• The term joist typically refers to any horizontal framing that supports a structure's interior floor or a flat roof. Builders use several materials as joists, including solid lumber, floor trusses and engineered I-joists. Solid lumber joists are the most common type of joist to receive bracing for structural purposes. Under special circumstances, floor trusses and engineered I-joists might receive bracing to fill gaps, provide support for special building features, or a nailing surface for plumbing, electrical or HVAC components.

Types of Joist Bracing

• Bridging and headers are common joist bracing techniques. The term bridging refers to installing blocks of wood perpendicular between adjacent joists. Although not always required by code, carpenters often install bridging to brace joists from twisting. Alternatively, carpenters might install blocks to provide a nailing surface for partition walls in the room above the joists. As with window and door openings, headers between joists support loads over a wide span. Where joist spacing deviates from the standard pattern, such as at a staircase opening in a floor, carpenters install a perpendicular header between adjacent joists. Headers are not optional; they compensate for missing joist support and safely transfer structural loads to surrounding joists.

Bracing for Fixtures and Appliances

• Ceiling-mounted appliances and heavy interior fixtures might require additional support or nailing surfaces in the form of joist bracing. For example, a recessed bathroom fan might not fit exactly between ceiling joists. Thus, the fan installer must fasten bridging or blocking between the joists to provide an installation surface for the fan. Alternatively, heavy appliances or plumbing fixtures, such as porcelain tubs, can exceed the recommended loads for a floor with small joists. To increase joist strength for heavy loads, builders might install additional joists or bracing beneath the fixture's installation area.

Suitable Materials

• Builders generally use solid, dimensional lumber to create braces between floor joists, such as 2-by-4 lumber. If you're bracing solid lumber joists to prevent twisting, use solid lumber of the same dimensions as the joists. Builders also use solid dimensional lumber to create blocking, support surfaces, or as nailing surfaces between engineered joists or floor trusses.