Sizing Floor Joist Beams

Joist span and spacing is set by your local building code.

Sizing floor joist beams. See the image below for an example of joists spaced 16 on center 16 o c. 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. Floor joists or beams provide the below surface support for the wood subfloor of a room. I asked my local building official how he checks a deck plan to make sure the joist size and spacing combination will meet requirements of the building code he goes to the 40 lb.

Live load is weight of furniture wind snow and more. 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. Maximum floor joist span for no. 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.

A structure with a 10 foot 3 05 m length and joists set 12 inches 304 8 mm apart would require using a floor joist size of 2 x 8 50 8 x 203 mm. 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. Our floor joist beam can span a maximum of 13. 2 grade of douglas fir are indicated below.

So we now have adequately sized floor joists and an adequately sized floor joist beam for our 24 x 13 house. 1 ft 0 3048 m. In the table above the widest floor beam span for 12 of supported floor joists is 14 7 if using a 5 ply 2 x 12. True floor joist span calculations can only be made by a structural engineer or contractor.

Live load floor joist span tables in chapter 7 of the state residential code based on the 2012 international residential code. 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. 2x10 to 15 feet and 2x12 to 18 feet. Bc calc performs engineering analysis to help our customers size beams joists columns studs and tall walls for their building projects.

It is simple to use yet flexible enough to analyze a variety of common applications. 1 psf lb f ft 2 47 88 n m 2. The floor joist spacing is the distance between the centers of any two installed joists. A 2x8 up to 12 feet.

Dead load weight of structure and fixed loads 10 lbs ft 2. 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.