how to attach porch to roof?

[rsc98584]

I’m planning to cover my deck with a light weight porch (deck roof) using clear corrugated plastic roofing material. This is not an enclosed porch, but one that would keep the rain off the deck and allow us to us it in the winter. In order to support the porch roof, I would like to go up about 18 inches on my existing roof and run 2 x 6 beams from the roof to the front “wall” of the porch. I would rather do this than attach the beams to the fascia. The fascia has a gutter attached to catch rain water anyway and I don’t particularly want to interfere with that. The roof has an angle of about 30 degrees. I’ve got everything figured out except this: How do I attach the beams to the roof and allow the water to run underneath to the gutters? I don’t really want to remove any of the composition roof. Instead, I want to attach the beams to the roof (on top of the shingles), but am not sure of the best method.

I hope this makes sense. If not, let me know. Thanks so much.



Randy Cox

Washington State

[Rich]

Randy,

First off, are you going to do a dormer (gable) type roof over the porch or just a shed style roof?
From what I've gathered it seems like a shed style roof would be easiest in your situation. I am a little confused where you say "How do I attach the beams to the roof and allow the water to run underneath to the gutters?"
In my opinion this will only cause problems down the road where the beams you install on the roof will be in contact with the elements and will probably rot pretty quickly. The best way to handle this is to cut holes in the roof and run the new rafters right beside the existing rafters. Then you can sheath the roof like normal and tie the shingles back in.
I may be way off base here but trying to understand your post more fully. Answer this or set me straight and I may be able to do a quick drawing for you.

[rsc98584]

Thanks for the reply. Yes, it will be a shed type roof. And yes, I too am concerned about the deck rafters resting on the roof and coming in contact with the elements and rotting. Is there a way to rest the deck rafters on a raised piece of metal or hard plastic? And then put a screw through the end of the rafter (and metal of plastic piece) directly into the roof and then waterproof the screw hole it some way?
I was trying to avoid any major construction or cutting into the roof, but maybe if you could explain that a little further I will have a better understanding of exactly what you mean by “cutting a hole through the roof” and attaching to the roof rafters.
Thanks very much for your help.
Randy

[Rich]

Well here's what I came up. It's nothing special but will give you an idea.

http://www.construction-resource.com/images/temp/shedrafter.jpg

[rsc98584]

Thanks for the diagram. I see now what you were describing. Thanks.

[harryc]

It sounds to me like you want to install the ledge board (terminology?) on some sort of "standoff", so you don't have to cut into the roof. Maybe like a peice of pipe or small block of wood attached to the roof, every 2 feet, then attach the ledger board to them so it "hovers" about 2 or 3 inches over the existing roof. The rafters then attach to it. You would almost defininately need to cut the shingles away where the standoffs attach, and install flashing to keep the water out. It sounds like it would work, but it does create alot of holes (potential leaks) in the roof.

An alternative to consider if adaptable to your configuration might be to build the patio roof as a freestanding structure with support posts along the outboard edge of the patio and also along the house edge. It could still be a shed style roof, the overhang on the house side could extend the 18 inches over your existing roof. If your existing house has a roof overhang that forces the inboard posts away from the house wall, you could incorporate them into plant hangers, shelves, benches etc., to make it look intentional.