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bluebird5 09-16-2013 07:26 PM

rafter sizing
Hello guys and gals. I am needing to size some rafters and have been using the american wood councel span calculator, but I have got a couple questions.

Does the dead load include the weight of the rafter itself along with the coverings or just the decking and shingles and insulation and drywall and such?

Also, how do I find the snow load for my area? I live in Nashville, Tn so it can either snow a lot or none at all.

I am spanning 24 ft on a 4:12 and was either gonna do 2x12x26 on 16's or 2x10x26 on 12's I'm leaning toward the 2x10's, but am not sure that I am calculating correctly yet.

Thank you

Mark Harvey 09-16-2013 07:57 PM

Bluebird, I can speak a little to my area. The rafter weight doesn't really matter as it is assumed the the structure will support total weight. The span is the big factor but 26 ft. isn't huge. Contact your local county or google a weather channel for your area, or even try "snow Load Nashville" and you should get some reasonable idea. Our snow can vary from light fluffy styuff to that heavy wet stuff, ... look at averages over a few years and make your decission. I'd go for over-kill rather that taking a chance for the sake of a few extra dollars. Keep in mind that any exrtas may also be a positive selling point whenever you might decde to sell.
Hope this helps.

Daniel Holzman 09-16-2013 08:09 PM

Dead load includes the weight of the rafter, which is typically pretty low. Dead load is always listed in the local building code, as is required live load and snow load. If you are unable to locate a copy of your building code, you can always talk to the building inspector, it is their job to know the code so they can certainly tell you what snow load to design for.

GBrackins 09-16-2013 09:23 PM

you'd have to check with your local building department to find out what you ground snow load is based upon your building code.

this link will provide you with rafter spans based upon your loads, hope it helps

good luck!

Clutchcargo 09-17-2013 04:52 PM

63 Attachment(s)
Aren't you into trusses once you have a span that big?

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