Band Joist

Definition

A band joist, also known as a rim joist, is a wooden joist that runs perpendicular to the direction of the floor joists. It is located at the outer edge of the floor platform and closes off the floor structure at the exterior face of the building.

Purpose

The primary purpose of a band joist is to provide structural closure to the ends of the floor joists, helping to distribute loads evenly and adding stability to the floor system. It also serves as an attachment point for the exterior walls, contributing to the overall integrity of the building's structure.

Examples of Use

1. Residential Construction: In residential buildings, band joists are used to frame the perimeter of the floor platform, supporting the exterior walls and distributing loads from above.
2. Deck Construction: In the construction of decks, band joists provide the necessary support at the outer edges, ensuring that the deck remains stable and secure.
3. Multi-Story Buildings: In multi-story buildings, band joists help to align and support the floors and walls, ensuring consistency and strength across different levels.
4. Additions and Extensions: When adding extensions to existing buildings, band joists are used to tie the new floor structure into the existing framework, providing continuity and support.

Related Terms

• Floor Joists: Horizontal structural members that support the floor loads and transfer them to the beams and foundation.
• Rim Joist: Another term for band joist, commonly used interchangeably.
• Sill Plate: The horizontal wood member placed on top of the foundation, onto which the floor joists and band joists are attached.
• Header Joist: A joist that runs perpendicular to the floor joists at the ends of a floor opening, such as for a stairwell or chimney, providing support for cut joists.

Notes

• Installation: Proper installation of band joists is crucial for maintaining the structural integrity of the floor system. This includes ensuring they are securely fastened to the ends of the floor joists and to the sill plate.
• Insulation: Band joists can be a source of heat loss, so it is important to ensure they are properly insulated to improve the energy efficiency of the building.
• Moisture Protection: Protecting band joists from moisture is essential to prevent rot and structural damage. This can be achieved through proper flashing, sealing, and ventilation.
• Connection Points: Band joists provide critical connection points for various building elements, including exterior walls, floor joists, and sometimes stair stringers, enhancing the overall stability of the structure.