Timber Roof Joists

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Timber roof joists. Let s consider a basic gable wood roof framing design. Floor beam span tables of residential structural design we will now look at roof rafter and beam design. Usually 400 450 or 600mm but any value can be used up to 610mm max usually 400 450 or 600mm but any value can be used up to 610mm max 1 2 timber strength class and joist size. These span tables apply only to flat roof and roof with a slope of up to 10 degrees.

This is the distance between joist centres. They are nominally 2 inches thick actual width usually 1 1 2 inches and come in a variety of widths from 8 to 12 inches. Timber to be covered these span tables do not apply to timber which is fully exposed to the elements. The image below shows a cross section of our simple 12 x 13 house from the joist span tables section of this tutorial.

Here we have a wood framed gable roof. Notches are not to exceed 0 125 of the depth of the joist and are to be located between 0 07 and 0 25 of the span from the support. Joists are traditionally made from timber.