Roof Joists Width

There are several variables to consider when determining the proper rafter size.

Roof joists width.

Let s consider a basic gable wood roof framing design. A roof joist is always spaced no more than 16 inches apart from another roof joist. Decreasing the distance between rafters to 12 inches however increases the maximum span to 14 feet 4 inches. For example 2 by 6 rafters made from select structural grade douglas fir that are required to support a live load of 20 pounds per square inch can have a maximum horizontal span of 11 feet 4 inches.

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 calculator for wood joists and rafters also available for the. Ceiling joist spacing in inches 12 16 19 2 24 species and grade of lumber. You should check with your local building department for construction requirements in your area.

The range of joist sizes used in homes varies though between 2 by 4 inches and 2 by 12 inches. Spacing in exterior exposure. 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. Ceiling joist span use this table to determine the maximum lengths of ceiling joists based on species of lumber joist spacing and joist size.

The image below shows a cross section of our simple 12 x 13 house from the joist span tables section of this tutorial. Floor joist span use this table to determine the maximum lengths of floor joists based on species of lumber joist spacing and joist size. Here we have a wood framed gable roof. If the roof is not completely square you can decrease the space between joists but never increase the space.

Live load psf dead load psf span calculator for wood joists and rafters available for the iphone. Continuing on from part 3. Now in order to correctly size ceiling joists lets take a look at a few examples. Weather you re building a shed roof or adding a dormer to your second story it is important to choose the proper size rafter.

Standard size of joists though there is no standard joist size for the ceilings in all buildings most average homes use ceiling joists in a board size of 2 by 6 inches. Various lumber size options 2 4 2 6 2 8 2 10 the maximum ceiling joist span based on the lumber size species grade and spacing used. Joist span and spacing is set by your local building code.