Floor Joist Size In Residential Construction

You should also check your local building codes before starting construction and consult a structural engineer in unusual or extreme situations.

Floor joist size in residential construction.

Choosing the correct floor joist size depends on your building application joist spacing and several other factors these include the length of the span as well as the type and grade of the lumber being used. This sample table gives minimum floor joist sizes for joists spaced at 16 inches and 24 inches on center o c for 2 grade lumber with 10 pounds per square foot of dead load and 40 pounds of live load which is typical of normal residential construction. Floor joist span tables for surveyors floor construction surveyors and structural engineers use data from tables below to help calculate the size of timbers necessary to give adequate support to timber floors. Additional support for the floor joists is achieved by nailing the ends of the joists into headers.

While most residential construction uses 2x8 joists with 16 inch spacing there are many other factors you need to consider when determining the proper joist span length. 2x10 to 15 feet and 2x12 to 18 feet. The larger the deck the larger the joists. Joist span and spacing is set by your local building code.

Putting all these factors together gives the minimum size joists needed for various types of wood grades of lumber sizes of boards spacing of joists and the load that will be placed on the floor. Solid lumber is generally the most economical choice for joists though price will vary based on wood species board size and lumber grade. True floor joist span calculations can only be made by a structural engineer or contractor. In typical deck construction with a ledger on one side of the joist and beam on the other the size of the joists is driven by the size of the deck and based on the general maximum spans mentioned above.

Joists must exhibit the strength to support the anticipated load over a long period of time. The following table gives details of allowable spans and spacing between joists for the most common timber sizes used in floor construction. All the figures are based on normal domestic floor loadings where the floor construction is typically 18 25mm floor boards sheets with up to 12 5mm thick plasterboard and skim underneath. When building a house or even a deck it is important to confirm you have the correct joist sizes spans and spacing before you get started.

Common joist spacings are 12 inches 304 8 mm 16 inches 406 4 mm and 24 inches 609 6 mm. Solid lumber joists were once the only option but modern building materials and construction technologies have rendered them less common in new homes. Considering the cross section of a typical joist the overall depth of the joist is critical in establishing a safe and stable floor or ceiling system.