Floor Joist Size In Residential Construction

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.

Floor joist size in residential construction.

In many countries the fabrication and installation of all framing members including joists must meet building code standards. 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. Joists must exhibit the strength to support the anticipated load over a long period of time. 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.

Solid lumber is generally the most economical choice for joists though price will vary based on wood species board size and lumber grade. 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. 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. The following table gives details of allowable spans and spacing between joists for the most common timber sizes used in floor construction.

2x10 to 15 feet and 2x12 to 18 feet. Section r502 10 of the international residential code states that header joists can be the same size as the floor joists when the header joist span isn t greater than 4 feet but if the header joist span is more than 4 feet you ll need to double the header joist and ensure that it s capable of. 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. 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.

Common joist spacings are 12 inches 304 8 mm 16 inches 406 4 mm and 24 inches 609 6 mm. True floor joist span calculations can only be made by a structural engineer or contractor. Joist span and spacing is set by your local building code. 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.

Solid lumber joists were once the only option but modern building materials and construction technologies have rendered them less common in new homes. You should also check your local building codes before starting construction and consult a structural engineer in unusual or extreme situations. A 2x8 up to 12 feet.