Floor Joist Standards

True floor joist span calculations can only be made by a structural engineer or contractor.

Floor joist standards. This extra surface area provides more support beneath the floor and also serves decorative purposes. The floor joist spacing is the distance between the centers of any two installed joists. Also available for the android os. A floor s framework is made up mostly of wooden joists that run parallel to one another at regular intervals.

Apa performance rated i joists pris are manufactured in accordance with pri 400 performance standard for apa ews i joists form x720 this performance standard provides an easy to use table of allowable spans for applications in residential floor construction allowing designers and builders to select and use i joists from various member manufacturers using just one set of span. In the past 2x4s or 2x6s were sometimes used as floor joists. 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 term beam generally refers to pieces of wood that run thicker than standard joists.

Ceiling joists are usually 2 by 6s or sometimes 2 by 4s if it is an older home. Instead of having a 2 inch surface area on which to place flooring beams may be 4 inches 6 inches or even wider. In buildings with basements the first level of floor joists serves the same purpose. Some newer homes have manufactured i beam shaped joists.

Joist span and spacing is set by your local building code. 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. Most decks use 16 on center spacing for joists. Some builders reduce joist spacing to 12 on center to strengthen the deck frame or to increase maximum.

See the image below for an example of joists spaced 16 on center 16 o c. Span calculator for wood joists and rafters also available for the android os. Floor joists installed on second or third or higher levels double as ceiling joists for the level below. Floor joists are typically 2 by 8s 2 by 10s or 2 by 12s.

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. The layout term for joists is on center which is the center to center measurement from one joist to the next.