Attic Joist Size

Uninhabitable attics without storage are those where the clear height between joists and rafters is less than 42 inches.

Attic joist size. You also need to ensure that the joist spacing is adequate. 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. You need 3 4 inch plywood. Attic joists that are made from 2x8s may be acceptable for building your attic floor but because every room is variable there are no absolutes.

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. Builders can adjust their choice of lumber size and spacing depending on circumstances. Although you can construct a garage using thicker stronger joists 2 inch by 6 inch joists are sufficient for most garages even if you intend to build an attic storage area above your garage. But you can still double the capacity of the existing 2x6s in the attic floor so first let s make sure that s enough for your situation.

Joist dimensions are only part of the equation. 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. Building code trainer 2020 therefore if you have an attic space according to this scenario the ceiling joists can be designed for a live load of 10 pounds per square foot psf by using table r802 4 1. 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.

My calculations tell me assuming 2 southern yellow pine joists which are common in my area that 2x6s 16 inches on center will span 9 feet 9 inches with allowable deflection being the governing factor. The dimensions of the joist depend on the span as well as the load it s intended to bear.