roofing

I'm trying to put a roof over my deck so I can screen it in.I am unable to come off of my overhang,so I need to come from my existing roof which is a 4 -12 pitch.How do I find the angle to cut my rafter coming from the roof.The roof edge is 98" above my deck and my deckcomes out 11'.At the edge of the deck I want to come up 80".Please advise.TonyZimmer

 

Normally, I just put the new rafters next to (sistered) the existing rafters from the house. The only cuts are at the two rakes of the roof. I lay the new rafter next to the last one on the house and make a line where the two meet....the perfect angle. Use a sawsall to cut the rectangular holes through the old roof and deck and slide the new rafters in and nail. The weight is supported by the same wall that supports the existing tursses or rafters. If you dont want the old overhang there, just cut it out with the sawsall, using the bottoms of the new rafters as a guide. Remember, your new roof deck will only have a slope of about 1 1/2:12, well below the minimum 3:12) required for shingles or other "shedding" roof systems. You'll probably need to go to single ply or BUR to be legal.

I hope i understand the situation correctly.