Floor Joist Sizing

The larger the deck the larger the joists.

Floor joist sizing. 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. 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. Since the example house we are designing for is 12 feet wide we need to find in the floor joist span table a joist size and centering that can span 12 or wider. Floor joist span tables for various sizes and species of wood.

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. Dead load weight of structure and fixed loads 10 lbs ft 2. The 1 grade material is more expensive than the 2 grade but if you can use fewer or smaller 1 grade joists or.

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. 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. The floor joist spacing is the distance between the centers of any two installed joists. Joist span and spacing is set by your local building code.

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. A 2x8 up to 12 feet. 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. 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.

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. The lengths and sizes of joists vary depending on the species and quality of the lumber used. Floor joists or beams provide the below surface support for the wood subfloor of a room. 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.

1 psf lb f ft 2 47 88 n m 2. Live load is weight of furniture wind snow and more. Maximum floor joist span for no. 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.