Attaching lean-to roof to existing barn

This was originally posted in the garage/car port section but the discussion evolved into a roofing question. I want to add a lean-to shelter along the length of an existing barn. The best option, given the height involved, is to attach to the existing 12/12 barn roof. The barn is fairly new with laminated shingles.

The question I had was the procedure to shingle up the new lean-to and blend into the existing barn roof. I am guessing that I need to lift the shingles on the barn (without damaging them) and somehow make sure that my new shingling job terminates in exactly the right spot to go under the existing barn shingles. How would I accomplish this?

Thanks!

 

You have a challenge, but not impossible. The reveal on most shingles is around 5 inches. What is the reveal on your shingles?

Once you determine the exact reveal measurement, then the bottom edge of the first course on the new roof needs to be a multiple of that measurement from the bottom edge of the existing shingles.

You will need to remove the starter shingle on the existing roof so the last course of new shingles will lay flat.

The pros will follow.