What Is Floor Joist Span

Floor joist span tables for various sizes and species of wood.

What is floor joist span.

You should check with your local building department for construction requirements in your area. 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. Floor joists on new construction. For example a 10 foot 3 05 m joist resting on a 6 inch 15 24 cm wall at either end has a design span of 9 feet 2 743 m.

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. Floor joist spacing is the distance a floor joist board can be separated from an adjacent floor joist. True floor joist span calculations can only be made by a structural engineer or contractor. Live load 30 lbs ft 2 1436 n m 2.

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. Additional support for the floor joists is achieved by nailing the ends of the joists into headers. Joists are often made from wood or steel.

1 psf lb f ft 2 47 88 n m 2. The heaviest joist along with the above factors will span a maximum of 23 feet 8 inches. The joists span across a room or other area are supported on their ends and sometimes in their middles by load bearing walls or beams. 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.

This length has a maximum safety capacity that is based on the width and material used to make the floor joist. See the image below for an example of joists spaced 16 on center 16 o c. With these factors the lightest joist will have a maximum span of 17 feet 8 inches. Joist span and spacing is set by your local building 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. Floor joists are horizontal framing members that make up the skeleton of a floor frame. Dead load weight of structure and fixed loads 10 lbs ft 2. 2 grade of douglas fir are indicated below.

Live load is weight of furniture wind snow and more. These tables can also be used to determine deck joist span. Maximum floor joist span for no. 1 in 25 4 mm.

The design span is the length of the joist measured from the face of the supports at either end. 1 ft 0 3048 m.