Standard Attic Joist Spacing

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.

Standard attic joist spacing.

In order to determine if an attic is considered an attic with limited storage the code describes it as the following. Builders can adjust their choice of lumber size and spacing depending on circumstances. This will support a room ceiling that is 10 feet long on one side as in 10 foot by 15 foot or 10 foot by 17 foot rooms which is a standard dimension for many rooms in residential construction. Now if the space is large enough to provide adequate space for storage the attic space shall be considered an attic space with limited storage.

Uninhabitable attics with limited storage are those where the clear height between joists and rafters is 42 inches or greater. It is safe to say though that 2x6 ceiling joists spaced every 24 inches on center a typical arrangement found in attics will not support live loads for a bedroom office or bathroom. You should check with your local building department for construction requirements in your area. Joist span and spacing is set by your local building code.

Sixteen inch oc spacing of ceiling joists made from 2 southern pine allows for a maximum 13 inch span length. Large room joist spacing. Span calculations for attic floors the best way to get your span calculations correct is to hire a structural engineer or contractor to run the numbers for you. Joist spacing and attic use the joist spacing in some attics is 24 inches and 1 2 inch sheets will sag and possibly break when spanning that distance.

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. Standard joist spacing for the installation of attic flooring materials is 16 inches on center oc meaning the distance from the center of one joist to the center of the next joist is 16 inches. Common spacing for trusses on this type of building is often between 2 and 4 feet but trusses built with advanced designs may allow spacing as great as 8 or 12 feet. So the space between rafters can be greater without reducing the maximum span.

Normally floor joists are spaced 16 inches apart on center. This means from the center of one upright joist to the center of the next. With some structures floor joists are required to be 12 or 24 inches apart on center. Given that 2x8s are actually 1 inches wide it works out to be 14 inches between each joist.