Expert: Dan Griffin - 7/21/2008

Question
We have added on to the side of our existing covered back porch.  We had a 6" concrete slab 16x24 poured that is tied into the side of the existing porch's concrete floor.  My question now is, what is correct way to tie the new roof of the 16x 24 addition into the existing roof. The pitch of the existing porch is 3/12 and we want to follow that same line.

One framer said he can just snap a line and remove shingles etc. and nail a 2x6x24 to existing roof and nail 2x6 rafters onto it and out the 16' to 2x12s.  Another says he needs to build a knee wall that is tied into main frame of back of house.  Both, of course, say they will have to cut off overhang.  
First guy says he is building a knee wall - it just doesn't tie into 2x12s on back wall of house. He says he will nail the 2x4s of his knee wall to sides of the 2x6 rafters and rest the bottom of the 2x4s on top of brick wall below.  Are they both correct/wrong?


Thanks very much.

Answer
Craig, how was the first porch roof done?  If it has worked, I would duplicate it.

I am a bit lost, though.  What is made of 2x12, what is made of 2x6?  I don't agree that 2x6 is strong enough to span 16 feet.  I am considering a 20 pound snow load and 10 pound dead load.  YOu never said where you live.  If the rafters are 2x12, you have a lot more snow than I do (very possible).

Both framers may be telling you the same thing.  The span is from your existing outside stud frame (not the brick) to the new outside wall/column line header or top plate.  It sounds like each of them intend to brace or pony wall down to the existing wall line.  Without seeing it or having a better explanation, I would suggest tieing the top end of the new rafters to the double plate and side nail to your existing house rafters or trusses.

If you are committed to the project, tear out enough of the end wall of the existing porch to see how the original was done, I think you have to tie into it anyway.