When calculating the span of joists or rafters, use the horizontal distance between vertical supports. The number 1 grade material is more expensive than the #2 grade, but if you can use fewer or smaller number 1 grade joists or rafters in your design, you may actually save money.ĭepending on the availability and cost of various size framing materials, it may be more economical to use larger joists or rafters in your design because you can typically use fewer of them. For example, you can span a #1 grade (no knots) southern yellow pine joist a greater distance than a #2 grade of the same species (with knots). The lengths and sizes of joists vary depending on the species and quality of the lumber used. To calculate maximum spans of additional species of lumber, use the Span Calculator or the Span Tables for Joists and Rafters on the American Wood Council website.Ĭonsiderations when using the Rafter and Joist Span Tables ![]() ![]() Contact your local building code officials to determine the building code for your area. Weigh all of the elements when designing wood structures. Some areas have wind and seismic conditions. For example, some localities get large amounts of snow, whereas others get none. First world problems.Before determining the maximum spans for joists and rafters, you must know the load requirements for your region. There's a 6 foot easement on that side to the fence, so the building wall will be reasonably close to the fence. OTOH, the north side where it will actually go did have the advantage that it could be closer to the "effective" line because the actual property line is about 7 feet into the neighboring property because of what had to be done when subdividing it years ago. It would be "logistically" and visually a lot better if it was on the south side rather than the north side but because of the required 15' side setback, a very large and mature willow tree would have to be destroyed. SWMBO is to not have the structure require removing any live trees. Positioning my own building has been an exercise because a "prime directive" for both myself and Professor Dr. Every property has its upsides and downsides. I'm sure that what you put up will meet the immediate need and you've mentioned that you do have a plan to move on in a few years to larger quarters. ![]() No way that would pass code now, but it's been there for 100 years and is still pretty straight. The funny thing i that the house is also 16 feet wide and has rough cut 2x4 rafters on 16" centers and a 12/12 pitch. If anyone knows of a rafter span table that goes up as high as 90# I would be very grateful to hear of it. It seems to me on a back of the envelope basis that full size 2x10 should be about right, but I am not an engineer. I think there is some extra strength in the full size rafters, too. It looks on the 70# chart like that would be okay, but I would need to go bigger for 90# presumably. They will be at 6/12 pitch, 24" centers and the span will be 8'9". I had specified full size rough cut 2x8 rafters on 24" centers. I would be happy to use whatever size rafters she told me to, but since neither of us knows what is sufficient I seem to be stuck unless I hire a structural engineer, which I would rather avoid if possible. The inspector also doesn't seem to know what size rafters are wanted. I can find rafter span charts for up to 70 psf, but nothing higher. The building inspector says that the roof must be designed for a 90 pound snow load. ![]() I have run into an obstacle in getting my workshop design approved.
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