Ceiling Joist Size Requirements

Size length of ceiling joists standard size of joists.

Ceiling joist size requirements. Although 2 x 4 s are included in the official table they are not listed because it is never advised to use them. This ceiling joist span table is based on the 2012 irc for uninhabitable attics with limited storage. A better choice would be using a 2 x 10 50 8 x 254 mm joist size.

For example the highlighted cell below shows that a 2 x 6 southern yellow pine joist with a grade of 2 and spaced 24 apart can have a maximum span of 10 feet 0 inches 10 0 if you are designing your structure to support a plaster ceiling. Span exceeds 26 feet in length. 2 x 12 s are not listed because you can span pretty much whatever you want.

1 inch 25 4 mm 1 foot 304 8 mm 1 pound per square foot 0 0479kpa. 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. Therefore given the above example the minimum allowable joist size for douglas fir larch 3 lumber spanning 15 0 is a 2 10 since it can span 15 5.

For a joist to have the most strength it should stretch all the way across a room from the top of one. A 2 8 member for example cannot be used since it can only span 12 7. Builders can adjust their choice of lumber size and spacing depending on circumstances.

Plain ceilings are sized at 10 lb loads while the ceilings with storage are sized for 20 lb loads. 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. Using grade 1 lumber will provide more structural support with a smaller joist size.

Ceiling joist spans for common lumber species uninhabitable attics without storage live load 10 psf l δ 240 check sources for availability of lumber in lengths greater than 20 feet. It covers 2 common lumber species and sizes at 20 pounds per square foot load. 2 x 6 ceiling joists 2 x 8 ceiling joists.