Floor Joist Standards

Some newer homes have manufactured i beam shaped joists.

Floor joist standards.

Most decks use 16 on center spacing for joists. The term beam generally refers to pieces of wood that run thicker than standard joists. Floor joists installed on second or third or higher levels double as ceiling joists for the level below. Also available for the android os.

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. A floor s framework is made up mostly of wooden joists that run parallel to one another at regular intervals. Instead of having a 2 inch surface area on which to place flooring beams may be 4 inches 6 inches or even wider. The layout term for joists is on center which is the center to center measurement from one joist to the next.

True floor joist span calculations can only be made by a structural engineer or contractor. 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. Ceiling joists are usually 2 by 6s or sometimes 2 by 4s if it is an older home. Joist span and spacing is set by your local building code.

Floor joists are typically 2 by 8s 2 by 10s or 2 by 12s. Most decking is not strong enough to support longer spans than 16. 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. This size is no longer acceptable when framing a structure.

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. See the image below for an example of joists spaced 16 on center 16 o c. This extra surface area provides more support beneath the floor and also serves decorative purposes. Span calculator for wood joists and rafters also available for the android os.

The floor joist spacing is the distance between the centers of any two installed joists. In the past 2x4s or 2x6s were sometimes used as floor joists.