Minimum Width Of Floor Joists

In the past 2x4s or 2x6s were sometimes used as floor joists.

Minimum width of floor joists. A structure with a 10 foot 3 05 m length and joists set 12 inches 304 8 mm apart would require using a floor joist size of 2 x 8 50 8 x 203 mm. Dead load weight of structure and fixed loads 10 lbs ft 2. Yellow pine douglas fir redwood hemlock spruce western red cedar eastern white pine. Common sense tells you that large floor joists can carry more load and spacing joists closer together also increases the load bearing capacity of a floor.

So the minimum is 18 for floor joists and 12 for wood beams within the building foundation according to the internaitonal residential code irc and the residential edition of the florida building code fbc r317 1 1 unless the wood is preservative treated or naturally durable. 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. The extra two inches of vertical distance when a floor is framed with 2 x 10 joists rather than 2 x 12s can be quite important for example.

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. Maximum floor joist span for no. In buildings with basements the first level of floor joists serves the same purpose. However when running spf 2 6 floor joists into the floor joist calculator referenced above you get a maximum span of 9 feet 8 inches with a minimum bearing length of 3 inches at each end on 12 centers.

Where continuous joist members are used the interior bearing supports shall be located within 2 feet 610 mm of midspan of the cold formed steel joists and the individual spans shall not exceed the spans in table r505 3 2. Floor joists installed on second or third or higher levels double as ceiling joists for the level below. If the joist spacing will be 16 inches 406 4 mm a joist size of 2 x 8 should be used even if the length is only 8 feet 2 44 m. Joist size 16 o c.

Floor joist size and thickness shall be determined in accordance with the limits set forth in table r505 3 2 for single or continuous spans. Below is a table giving the minimum size floor joists needed for 16 and 24 on center o c spacing when using 2 lumber with 10 pounds per square foot of dead load and 40 pounds of live load. 1 psf lb f ft 2 47 88 n m 2. But larger is not always better when builders are constructing a home or adding a room addition.

2 grade of douglas fir are indicated below. This a rough guideline.