Joist

Definition

A joist is one of a group of light, closely spaced beams used to support a floor deck or flat roof. In wood frame construction, it is a piece of lumber, two or four inches thick and six or more inches wide, used horizontally as a support for a ceiling or floor.

Purpose

The primary purpose of a joist is to provide support for floors or ceilings, distributing the load to the walls or beams. Joists are essential components in building structures, ensuring stability and strength.

Examples of Use

1. Floor Construction: Joists are used to support the floorboards in residential and commercial buildings.
2. Roof Support: In flat roof constructions, joists provide the necessary support for the roof deck.
3. Ceiling Framework: Joists support the ceiling materials and fixtures in various building types.

Related Terms

• Beam: A larger horizontal structural element that supports joists and other loads.
• Rafter: A structural member used to support the roof, running from the ridge to the wall plate.
• Decking: The flat surface supported by joists, often forming the floor or roof.

Notes

Joists must be installed with proper spacing and securely fastened to ensure the structural integrity of the floor or ceiling. The size and spacing of joists depend on the load requirements and span length.