What does joist mean?
A joist is a horizontal structural beam that supports a floor, ceiling, or roof. In a typical wood-framed building, joists run across a span and rest on walls, beams, or other supports, forming the framework to which flooring, ceiling boards, or roofing materials are attached. The word is used especially in construction, carpentry, architecture, and property inspection. Joists may be made from timber, engineered wood, metal, or other materials depending on the building and design. When describing a house, a phrase such as “exposed joists” often refers to beams deliberately left visible as part of the interior style, while “joist hangers” are metal connectors used to attach joists to supporting structures. Understanding the term is useful for reading building plans, discussing repairs, and identifying structural elements in a building.
nounA horizontal structural member that supports a ceiling, floor, or roof, especially in a building.
- A horizontal timber or other structural member spanning a space and supporting a floor, ceiling, or roof.
"The carpenter replaced the damaged joist beneath the upstairs floor."
"The inspection revealed termite damage in several floor joists."
"Insulation was installed between the roof joists before the attic was finished."
The plural is regular: one joist, two or more joists.
"Several joists were replaced during the renovation."
Joists are the hidden framework that gives a floor or ceiling its strength, even after the walls and finishes hide them.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does joist come from?
The word was borrowed into Middle English from Old French joiste. Its precise ultimate origin is uncertain, and older forms are recorded with several spellings. The modern form has remained a specialist term in building construction, with its sense centered on a beam that supports flooring, roofing, or ceiling material.
How joist is actually used
In British English, the term is especially associated with timber floor and ceiling construction; in American English it is also commonly used for roof framing.
Easily confused with joist
A joist is a structural beam, whereas a joint is a place where two parts meet or are connected.