Where is the best place to get info on what size rafters to use for a 12′ span. Want to build a shed roof on a 12′ x 24′ attachment to an existing 24′ x 24′ garage? Will be in RI and need to account for heavy snow.
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Go here http://www.cwc.ca/design/tools/calcs/SpanCalc_2002/
I have used this a lot to check designs.
In your case, you'll need to know what your snow load is. The calculator goes to 50 psf snow load, which is probably more than you'll need for your location.
If you are just winging this and don't have to show engineered plans to a building inspector, just use the 50 psf snow to be safe, and go with what the program says.
And remember, your spans have only to do with the horizontal clear run between end supports or bearings. Pitch doesn't come into play.
Edited 11/20/2005 10:20 am ET by Stinger
A quick call to your local building inspector would do. This isn't an issue for guess work. In my area snow loads range from 60 to 200 psf within a 20 mile radius.
Scott.
Edited 11/21/2005 7:46 pm ET by Scott