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Old 02-15-2011, 09:09 AM   #1
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Roof Over Deck


I have a 16' wide by 12' foot deep deck off my house. I am in the south and only get 6" of snow a year. The existing deck is built on eight 6x6 posts and is 2.5 feet off the ground. I wanted to cover my deck, so I obtained a permit to do so. Because it would go into my setback, I was not allowed to attach to the house, only to the existing deck.

I have completed the frame Using 4x4 posts, I built the frame of the deck cover, with 2x6 joists on 24" centers. On the far side of the deck, the furthest side from the house, I have four 4x4 posts. I have no posts in the middle, and 2 posts closest to the house. What this means is, I have a 15' 2" span that the back 2x6 (one closest to the house) travels before hitting the other 4x4. Is this too far for 2x6 ceiling band? If so can I sister another 2x6 and be OK?

Next question, my pitch is 1ft 5in drop over 12 ft. It is the most pitch I could get without sacrificing too much headroom at the far end. I know shingling is not the best method for this pitch, but since it is just a cover over a deck, what are some methods I should follow to make it the best I can? I would like to keep it shingles so it looks like the rest of the roof. Thanks

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Old 02-16-2011, 12:51 PM   #2
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Roof Over Deck


Any ideas?

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Old 02-16-2011, 02:02 PM   #3
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Roof Over Deck


Metal is a lot lighter than shingles, especially since you don't need decking.

It sounds like you're saying you want to support half the weight of the roof over a 15'-2 span with a single 2x6.

The biggest span I can find for a 2x6 is 12 feet. Without knowing the grade of your lumber, you can support 375 to 800 lbs. If you double it up, you can double the weight capacity.

You probably have 200 lbs of rafters. If you put up 1/2 inch decking then you have 360 lbs of that. Singles are some 200 lbs per square -- say, 400 lbs. So if you shingle you have about 1000 lbs. To calculate the snow load you need to know the greatest ever, not the typical. Your typical snowfall implies a load of 2000 or so lbs. Plus you need to allow for wind. Half the load goes to each end.

Now if you put a post in the middle of the span (on the deck) then you only have an 8 foot span, and a single no.3 2x6 will support 567 lbs. You are now dividing the 1500 lbs in half -- you need two 2x6, or 3 to be safe. If you can't put a post in the middle I don't have a table with values, but I'd guess you'd need more than double -- five or six.

I'm far from an expert at this kind of thing, so don't build it that way on my advice. You can find the tables I used here: http://www.awc.org/

EDIT: I found the span tables for longer spans. For a 15'-0 span they don't give values for a 2x6, but a 4x6 supports 700 lbs. A 6x6 supports 1100 (assuming no. 3 lumber). Three 2x6 is not the same as 6x6! Going back to our 8'-0 span, a 2x6 supports 567#, but a 4x6 supports 1323#. So a double 2x6 is only 85% the strength of a 4x6 (at an 8' span)

Last edited by pyper; 02-16-2011 at 02:11 PM.
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Old 02-16-2011, 02:06 PM   #4
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Roof Over Deck


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Originally Posted by pyper View Post
It sounds like you're saying you want to support half the weight of the roof over a 15'-2 span with a single 2x6.
I actually have 3 cross beams. So would it be a 1/3 of the weight?

Last edited by Bob Haskett; 02-16-2011 at 02:19 PM.
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Old 02-16-2011, 02:47 PM   #5
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Roof Over Deck


Since you have a center beam, it supports half the load; each end gets 1/4.

The diagonal bracing will help some too.
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Old 02-16-2011, 02:54 PM   #6
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Roof Over Deck


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Originally Posted by pyper View Post
Since you have a center beam, it supports half the load; each end gets 1/4.

The diagonal bracing will help some too.
So knowing I have a center beam, should I even bother sistering another 2x6? Or leave it as is? By the way, the product I have decided on is Mule-Hide SA-SBS roofing. Should be lighter than shingles, but not as light as metal.

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