What size wood are floor joists?
There are several different sizes and types of floor joists. The most common sizes are 2×8, 2×10, and 2×12.
What are joist sizes?
Joist Span Tables
| Yellow Pine, Douglas Fir | Western red cedar, Eastern white pine | |
|---|---|---|
| Joist Size | 16″ o.c. | 16″ o.c. |
| 2×8 | 12′ 8″ | 10′ 5″ |
| 2×10 | 16′ 0″ | 12′ 9″ |
| 2×12 | 18′ 6″ | 14′ 9″ |
What timber is used for floor joists?
Lumber Grade Lumber graded as #2 is the most common choice for floor joists and other framing lumber. It has more knots and defects than higher grades, but usually not enough to cause significant loss of bending strength.
How far can a floor joist span without support?
The maximum distance a 2×6 can span, according to the 2018 IRC, for a floor joist, is 12′-6”, ceiling joist 20′-8”, rafter 18′-0”, deck board 24”, deck joist 9′-11”, deck beam 8′-3”, and 6′-1” as for header. Always check the codes for determining factors or consult a Structural Engineer.
How do I work out my joist size?
For example, assume the clear span is 15 feet 6 inches. Round up to 16 and divide this span by 2, giving you 8. Next, add 2 to get the required joist depth. In this example, 8 + 2 = 10, so a 2×12 floor joist will be required (it’s important to use the actual lumber dimensions, not the nominal dimensions).
How do I choose the right size joist?
How big of a floor joist do I Need?
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). With a joist spacing of 24 inches (609.6 mm), the same 2 x 8 barely meets the minimum requirement for 8 foot (2.44 m) lengths. A better choice would be using a 2 x 10 (50.8 x 254 mm) joist size.
How big should a Douglas fir floor joist be?
Therefore given the above example, the minimum allowable joist size for douglas fir-larch #3 lumber spanning 10′-0″ is a 2×8 since it can span 10′-3″. A 2×6 member for example cannot be used since it can only span 8-1″.
Where do you find wood floor joists in IRC?
The design and construction of wood floor joists are found in Section R502 of the International Residential Code (IRC). Section R502 outlines the wood floor framing criteria which also includes prescriptive span tables.
What is the distance between two joists on a table?
The floor joist spacing is the distance between the centers of any two installed joists. See the image below for an example of joists spaced 16″ on center (16″ o.c.).