A band joist is a horizontal framing member that caps floor joists and helps support exterior walls in wood-frame construction.

A band joist, also known as a rim joist, is a horizontal framing member installed around the perimeter of a floor system. It closes off the ends of the floor joists and ties them together, providing structural stability and a nailing surface for exterior wall framing.

In residential and light commercial construction, the band joist plays a key role in transferring loads from exterior walls to the floor system. It also helps resist lateral movement of the joists and maintains the overall rigidity of the structure. Band joists are typically made from dimensional lumber, engineered wood, or structural composite materials.

Beyond its structural function, the band joist is an important area for energy efficiency and moisture control. Because it sits at the junction between floors and exterior walls, it is a common source of air leakage if not properly sealed and insulated. Proper detailing, including insulation, air sealing, and moisture protection, is critical to long-term building performance.

Because band joists sit at a structural transition point, they’re one of the most common locations where energy auditors find air leaks during building inspections.

• Ceiling Joist
• Deck Joist
• Floor Joist