Attic Joist Spans

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.

Attic joist spans.

Span exceeds 26 feet in length. Live load is weight of furniture wind snow and more. For example a joist made from doubled 2 x 6s can span a distance about 25 percent more than a single 2 x 6 but a 2 x 12 can span about 80 percent more than a 2 x 6 even though it has the same amount of wood as a doubled 2 x 6. Section r502 10 of the international residential code states that header joists can be the same size as the floor joists when the header joist span isn t greater than 4 feet but if the header joist span is more than 4 feet you ll need to double the header joist and ensure that it s capable of supporting the floor joist framing.

Live load 30 lbs ft2 1436 n m2 maximum span ft in nominal size. Dead load weight of structure and fixed loads 10 lbs ft2. Span length is different for every room. Now lets take a look at those tables.

The width is considerably more important than the thickness of a board. Trus joist tji ceiling span roof systems library builder i joists faqs roof truss design of timber structures garage attic ion the journal boardceiling joist and rafter spans home owners. 1 psf lbf ft2 47 88 n m2. 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.

So span length and width between the spans can be determined only by calculations. 1 in 25 4 mm. 1 inch 25 4 mm 1 foot 304 8 mm 1 pound per square foot 0 0479kpa. Joist span and spacing is set by your local building code.

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. For uninhabitable attics without storage we will use table r802 4 1 and for uninhabitable attic with limited storage we will use table r802 4 2. 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.