Joist

Joist
A roof made with a concrete slab with concrete joists

A joist, in architecture and engineering, is one of the horizontal supporting members that run from wall to wall, wall to beam, or beam to beam to support a ceiling, roof, or floor. It may be made of wood, steel, or concrete. Typically, a beam is bigger than, and is thus distinguished from, a joist. Joists are often supported by beams and are usually repetitive.

The wider the span between the supporting structures, the deeper the joist will need to be if it is not to deflect under load. Lateral support also increases its strength. There are approved formulas for calculating the depth required and reducing the depth as needed; however, a rule of thumb for calculating the depth of a wooden floor joist for a residential property is half the span in feet plus two inches; for example, the joist depth required for a 14-foot span is 9 inches. Many steel joist manufacturers supply load tables in order to allow designers to select the proper joist sizes for their projects.

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Engineered wood products such as I-joists gain strength from the depth of the floor or the height of each joist. A common saying in the industry is that deeper is cheaper, referring to the lower quality but often more cost effective joists designed for joist depths of 14 inches or more.

Bandsill is another term for joist used by construction workers and home inspectors in the southeastern United States.

See also


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  • Joist — (joist), n. [OE. giste, OF. giste, F. g[^i]te, fr. gesir to lie, F. g[ e]sir. See {Gist}.] (Arch.) A piece of timber laid horizontally, or nearly so, to which the planks of the floor, or the laths or furring strips of a ceiling, are nailed;… …   The Collaborative International Dictionary of English

  • Joist — Joist, v. t. [imp. & p. p. {Joisted}; p. pr. & vb. n. {Joisting}.] To fit or furnish with joists. Johnson. [1913 Webster] …   The Collaborative International Dictionary of English

  • joist — [joist] n. [ME giste < OFr, a bed, couch, beam < gesir, to lie < L jacere, to lie, throw: see JET1] any of the parallel planks or beams that hold up the planks of a floor or the laths of a ceiling: see FRAME vt. to provide with joists …   English World dictionary

  • joist — [dʒɔıst] n [Date: 1300 1400; : Old French; Origin: giste, from Latin jacere to lie ] one of the beams that support a floor or ceiling …   Dictionary of contemporary English

  • joist — [ dʒɔıst ] noun count a long piece of wood or metal put below a floor or ceiling to support it …   Usage of the words and phrases in modern English

  • joist — (n.) early 14c. (late 13c. in Anglo Latin), from O.Fr. giste beam supporting a bridge (Mod.Fr. gîte), noun use of fem. pp. of gesir to lie, from L. iacere to lie, rest, related to iacere to throw (see JET (Cf. jet) (v.)). Notion is of wooden beam …   Etymology dictionary

  • joist — ► NOUN ▪ a length of timber or steel supporting part of the structure of a building. DERIVATIVES joisted adjective. ORIGIN Old French giste beam supporting a bridge , from Latin jacere lie down …   English terms dictionary

  • joist — 1. noun A piece of timber laid horizontally, or nearly so, to which the planks of the floor, or the laths or furring strips of a ceiling, are nailed; called, according to its position or use, binding joist, bridging joist, ceiling joist, trimming …   Wiktionary

  • Joist — Recorded in England in a wide range of spellings including Jest, Jeste, Joce, Jose, Joist, Jost, Joust and Joost, this is a surname of Germanic, Dutch, Breton and Norman Franch origins. It is a cognate of the surname Joyce , itself deriving from… …   Surnames reference

  • joist — [14] Etymologically, a joist is a wooden beam on which boards ‘lie’ down. The word’s ultimate ancestor is the Latin verb jacēre ‘lie down’ (from which English also gets adjacent). Its neuter past participle jacitum was taken into Old French as a… …   The Hutchinson dictionary of word origins

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