Shed roof attached to existing home

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Old 02-22-12, 08:32 AM
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Shed roof attached to existing home

I'm building a 2/12 shed roof over a deck attached to a 6/12 existing roof on the home.

My rafters will go from a beam on post across a knee wall on an existing outside wall of the house, and then connect to the existing roof of the home.

Because of the length, I'll run a 2x6x14 from the outside deck wall to the knee wall, and attach a 2x6x8 to the 2x6x14 to continue onto the existing roof. These will connect at the knee wall.

I'll attach a drawing to show my measurements.

Can I attach the knee wall directly onto the existing shingles, or do I need to peel away the shingles and attach to the plywood sheathing?

And is a knee wall made out of 2x4's adequate or do I need 2x6's. I'll attach a photo/drawing to show my measurements.

Can you give me a link regarding how to construct the knee wall?

Also, where the rafters attach to the existing roof, do I need to nail a 2x6 to the existing roof and attach the rafters to/over the 2x6, or just nail the rafters on top of the sheathing where the house rafters are joined to the sheathing? I'm not yet sure if my added rafters will match exactly to the existing rafters, but I'm sure I can make that work if necessary.

Thanks for your help.

Keith

 
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Old 02-22-12, 03:15 PM
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The support wall can't sit on the roof. It must be carried down to the structural members of the house or banded as you suggested across the tails of your existing roof. Next, a 2x6 can't span 14', so you will have to beef up the size of your lumber, or construct support such as a truss system. In most instances it is best to remove the shingles and decking, to attach your rafters to your existing rafters. I question this, because if you leave the decking in place, at least you won't have a hole in your roof when and if the shallow roof is blown off via a hurricane or strong winds. Without solid walls and windows, basically you have a parachute sticking out from your house.
 
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Old 02-24-12, 01:10 PM
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Chandler...thanks for your response.

If I've calculated correctly, my 2x6's rafters would only span 12 feet between supports, with a 1' overextension on the outside wall. I had planned on using 2x6x16 at 16" O.C. and letting the overage on the house/roof side extend over the knee wall, and then attaching more 2x6x8's to continue on to where it intersects the house. Using a 2x6x8 to extend approximately 6 feet would leave me about 2' from each rafter to join together at the knee wall. I'm not sure if I'm explaining that properly.

Would that work or not?
 
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Old 02-24-12, 03:45 PM
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Depending on the lumber you are using for the rafters. Southern Pine will span 12' 9", so you are good, there. SPF (spruce, pine, fir) will only span 11'5". What type wood are you planning on using?
 
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Old 02-24-12, 04:58 PM
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Southern Pine is probably the cheapest, and my likely choice.
 
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Old 02-25-12, 05:00 AM
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Your overlapping of the rafters is find, just remember you are changing the center marks of your decking by 1 1/2", so take that into consideration, that is unless you sister the 2x6's their full 6' length. Otherwise, that part of the roof is supportable. You have addressed how the 2x6's will rest on the tail end, I am sure.....birds mouth on proper plate, hurricane straps, etc.
 
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Old 02-25-12, 06:23 AM
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I only plan to sister the shorter 2x6's on the ends, for cosmetic reasons.

Should I use bird's mouth cuts and hurricane straps on both ends? Or just on the outside wall ends, farthest from the house? And just toe nail the 2x6's into the knee wall?

Thanks for your input.
 
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Old 02-25-12, 12:03 PM
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Chandler...I've measured for my knee wall and will be just under the 12'9" span for the 2x6 rafters.

However, I have another question regarding attaching the knee wall to the existing roof. My roof does not have architechural shingles, and are rather flat against the house. By pulling up one layer of shingles, I'll have a flat surface to attach the knee wall.

My plan was to use a 2x6 for the base plate of the knee wall, with 2x4(16" O.C.) supports capped with a double 2x4 plate on top. All made in one piece(almost 14' wide). It would be much easier to mount the knee wall on the roof, if I first attached a 2x6 base plate to the roof, and then mounted my knee wall onto the base plate. By doing that I could be sure that my base plate against the deck will be attached directly to the rafters of the house. Also, it'll be much easier to square up on 2x6 instead of wrestling with the knee wall on top of the house, trying to square it up.

Does that sound feasible?
 
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Old 02-25-12, 03:54 PM
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Rock and roll!!! Let us know if you get stumped or need more help. Others may chime in here afterwards, so keep checking back.
 
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