Need help sizing roof rafters, floor joists, or beams? In this section, I cover how to size floor joists, beams and roof rafters on three different levels. The first level is titled "General Guidelines" and is for those people that don’t want to have to make any calculations or look up numbers in lumber span tables. The second level is for individuals that want to size beams, roof rafters, or floor joists outside of the parameters of my General Guidelines. At the second level, I provide simplified tables and show you how to use lumber span tables. Finally, the third level is for the more studious type wherein I provide detailed, engineering calculations to help you get the size right for beams, floor joists, or roof rafters under various loading conditions.

Some of the interesting topics discussed in this section deal with the relationship between the length of floor joists and beam size. More specifically, you’ll see how to balance the length of floor joists, beam size, and pier spacing to come up with a workable combination for your soil type and overall deck size. Further discussion includes how to determine the load roof rafters place on wall headers/beams and how to size them accordingly. Along the way, you'll read an explanation on why lumber span tables, while being technically accurate, sometimes result in sizing floor joists that are too springy.

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