Floor Joist Sizing

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 sizing. Joist span and spacing is set by your local building code. The lengths and sizes of joists vary depending on the species and quality of the lumber used. Dead load weight of structure and fixed loads 10 lbs ft 2. Floor joists or beams provide the below surface support for the wood subfloor of a room.

Common joist spacings are 12 inches 304 8 mm 16 inches 406 4 mm and 24 inches 609 6 mm. 2x10 to 15 feet and 2x12 to 18 feet. 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. For example you can span a 1 grade no knots southern yellow pine a greater distance than a 2 grade with knots southern yellow pine.

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. Floor joist span tables for various sizes and species of wood. Joist span table use these tables to determine floor joist spans based on grade of lumber size of joist floor joist spacing and a live load of 30 lbs ft 2 or 40 lbs ft 2 these tables can also be used to determine deck joist span. The larger the deck the larger the joists.

Though joists may be any size that you desire using typical floor joist and beam specifications ensures that you can find hardware to fit the joists and that the floor provides adequate support for furniture and other items in a room. 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. 1 ft 0 3048 m. Live load is weight of furniture wind snow and more.

Surveyors and structural engineers use data from tables below to help calculate the size of timbers necessary to give adequate support to timber floors. See the image below for an example of joists spaced 16 on center 16 o c. These tables can help calculate whether floor joists are strong enough to support themselves and the load they carry without the help of any walls underneath. 1 psf lb f ft 2 47 88 n m 2.

A 2x8 up to 12 feet. The 1 grade material is more expensive than the 2 grade but if you can use fewer or smaller 1 grade joists or. Maximum floor joist span for no. True floor joist span calculations can only be made by a structural engineer or contractor.

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.