Bar joists are structural components used for framing floors or roofs. They consist of parallel cords connected by intersecting supports and distribute weight to walls or foundation. Joists can be made of wood, steel, or composite materials. They are classified using an alphanumeric identification system and offer advantages such as prefabrication, precise construction, and reduced waste. However, they are more expensive than stick framing and require specific design criteria.
A bar joist is a structural component used to frame floors or roofs. The bar joist consists of a pair of parallel cords connected by a series of intersecting supports known as “cobwebs”. Bar joists feature a similar design to trusses, including the same triangular mesh pattern, but are generally smaller and lighter than most trusses. The design of these joists helps distribute the weight of a floor or roof structure to the walls or foundation at either end of the joist. A bar joist can be made of wood, steel or composite materials depending on the application and loads.
Each bar joist must be carefully selected based on the loads it will support. This includes the weight of building materials as well as people and furnishings. A structural engineer or architect can help installers select these joists using information such as required span, building design, and local building code requirements.
Many manufacturers and industry personnel use an alphanumeric identification system, such as 12K8, to classify different types of joists. The joist often contains a stamp or tag containing this code, which can help buyers and installers identify the joist. The code begins with a number, which represents the depth of the joist in inches. Each depth measurement is followed by a group of letters, representing the joist design. A “K” indicates a standard joist, while “CS” is used to identify joists designed to support point loads. Other special designations are used to identify very long, deep or oversized joists.
At the end of each code is a second set of numbers. This figure identifies the type of chords used in each joist. Each particular chord size and thickness corresponds to a corresponding number, which is constant across different joist materials.
Bar joists offer several advantages over traditional post or beam construction. Most joist systems are prefabricated in factories and arrive at job sites ready to assemble. This helps speed up the construction process and reduce labor costs. A prefabricated bar joist is also more precisely constructed than most structures that are field framed. This improves building safety and results in a more durable and stable structure. The joist construction also reduces overall waste, which helps reduce disposal and transportation costs.
One major drawback of bar-joist construction is the high cost of the joist compared to stick framing. While this cost is often offset by labor and disposal savings, stick framing is still cheaper in terms of initial cost. Since the joists must be prefabricated according to specific design criteria, there is also the risk of wasting design and engineering time.
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