Rafter Spacing for Flat Roofed Carport?
I am considering building an 18ft by 20ft, flat roofed carport with a 2:12 slope. I live in Washington, DC, I understand the design snow load is 30 psi. I am trying to get an idea for rafter size an spacing. The span would need to be 18ft. I plan on having 6, 6×6 posts set in concrete. Roofing material will be sheet metal. What size lumber will I need for rafters and beams, what spacing will I need, should I have noggins?
First you must understand the dead load. This is the total weight of the materials you use to build the roof.
Now the live load is when you add lbs. per sq. foot for projected snow,wind,rain loads.
To span 18′ and have it just support itself (dead load) without sagging I would use 2" x8"s on 16" centers. To make a nice job and a lasting job I would use 2" x10" s on 16" centers.A 2"X 6" roof would be a joke on an 18′ span. It would be dangerouse to install the roofing on this undersized framing.
Don’t risk a shoddy, saggy roof to save a few bucks- it would look terrible and a heavy snow would drop it like a rock.
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I assume you mean a shed roof? Higher on one end than the other. Is it free standing? For that distance I would look at having some metal truss’ made. Were around $2 foot prob around $4-6 now. Then you could space them 8′ apart and you place 2 x 4′s across in cleats to install the tin on. You would come out with less expense.
References :
Here is a table with all the spans and spacing through SouthernPine…Should be pretty much standard.. It even gives snow load… http://newstore.southernpine.com/images/ref202.pdf
In the end, it must be able to pass a building inspection. To be certain that you will be able to meet / exceed your local code, contact your local building officials. They will be able tell you what you will need to do to build a carport that will stand up to your wind and snow loads. Then you will have the info to draw your plans for your building permit.
References :
First you must understand the dead load. This is the total weight of the materials you use to build the roof.
Now the live load is when you add lbs. per sq. foot for projected snow,wind,rain loads.
To span 18′ and have it just support itself (dead load) without sagging I would use 2" x8"s on 16" centers. To make a nice job and a lasting job I would use 2" x10" s on 16" centers.A 2"X 6" roof would be a joke on an 18′ span. It would be dangerouse to install the roofing on this undersized framing.
Don’t risk a shoddy, saggy roof to save a few bucks- it would look terrible and a heavy snow would drop it like a rock.
References :
G.C.