![]() for a rafter without an attached ceiling (deflection L/180) to span 20' using #2 grade spruce-pine-fir (SPF) lumber (typical for my area) I would be allowed to span 21'-5" at 16" o.c. See Table R301.7 for Deflection Limits.įor example in my area our ground snow load is 30 psf. Also the type of ceiling to be attached, if any. You will need to know what species and grade of lumber you will use for the rafters, and again your ground snow load. This link will provide you with the Prescriptive Rafter Spans from the 2009 International Residential Code. Typically at a minimum live load is 20 pounds per square foot, unless your ground snow load exceeds it.Īlso, should you plan on using the "flat roof" as an elevated deck you would need to account for the live loads associated with this use. Live loads are based upon loads that may change, such as snow and people. This would require a call to your local building department to determine what your ground snow load requirements are, whether you need a building permit, and what drawings you would need to submit.ĭepending on your roofing materials a typical low-slope membrane and framing will be around 10 pounds per square foot for dead load. I just want something that will last and won't collapse if we get a foot of snow (which happens every couple of years).Īs tony.g said you have to know what your loads are. ![]() The roof will be treated like a deck - I plan on fiberglassing it and maybe have the odd BBQ on it with 5 people.ĭoes this sound ok? The inspectors in our city seem to let anything go through in respect to sheds and garages. I'll run two rows of blocking to keep twisting down and glue and screw t&g 3/4 plywood on the roof. There will be a slight pitch to the roof as I plan on having an extra 2 or 3 top plates on one supporting wall, to make it around 5" taller than the other. ![]() I've been reading (googling) about spans and from what I can tell, I should be able to run No 2 Douglas Fir 2x12 "joists" the full 20 feet span of the ceiling without any problems, preferrably spaced at 12" oc. I want to build a relatively flat roof for simplicity's sake and to keep the overall building height low. I have the walls up - 2圆 8' studs spaced 16" oc. I'm a long time reader, first time poster.
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