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What is a Timber Joist?

A. Leverkuhn
A. Leverkuhn

A timber joist is a wooden part of a construction that supports a load. Common types of joists include ceiling joists and floor joists. Joists in ceilings or in flooring are often set perpendicular to horizontal elements that make up a floor or ceiling.

In floor systems, joists are generally spaced evenly, and are covered with specificly sized boards that will run from one joist to another. Carpenters cut flooring pieces to run between a specific number of joists. This provides stability for a floor.

View of second story timber floor joists from below.
View of second story timber floor joists from below.

Although steel joists, or beams, made from other materials are common in commercial and public works construction, timber joists are among the most common elements of residential construction. Residential timber joists may be hidden, as in many conventional floors, or exposed in some types of ceilings and roof designs. When timber joists are exposed, they can provide a great decorative look for a space. Exposed joists can either make a room look rustic, or provide a kind of modern "transparent" design.

Floor joists on new construction.
Floor joists on new construction.

Among the different kinds of timber joist used in homes, a cantilever joist design is one that provides for specific aesthetic appeal. In a cantilever timber joist, one end of the joist is built into a ceiling or roof structure, and the other end extends into open space. Cantilever construction refers to beams that are supported on only one end. The load is physically distributed so that the open end of the beam can handle weight.

Homeowners and designers have come up with different uses for the cantilever timber joist. The open ends of a joist can be used to support an overhang that provides shelter for an outdoor area. They can also support hooks for flower pots or other decorative arrangements. Those who are designing exposed timber joist setups should always make sure the wooden joists are properly protected from precipitation, or are weatherized if exposed.

In the physical construction of a floor or ceiling, the timber joist provides much more than decoration. Modern building codes provide required spacing for timber joists and other joist types that will ensure solid load bearing capacity in a home or other building. Professional carpenters, architects and builders must be careful to complying with the requirements for joist configuration in order to facilitate safety in construction design, and to make sure that a building will stand the test of time. Knowing about some of the basic conventions for floor and ceiling joists can be helpful for anyone involved in crafting the construction of any home or building.

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    • View of second story timber floor joists from below.
      By: Howard Sandler
      View of second story timber floor joists from below.
    • Floor joists on new construction.
      By: Gord Webster
      Floor joists on new construction.