Hi, planning a 400 sq ft addition to my hip roofed home. I will be attaching the ridge board to the existing roof, then laying a flat board against the existing roof, creating the "valley" of the old and new roofs intersecting. Do I have to remove the shingles in that area? Specifically under that flat board the the jack rafters will be nailed to? Thans!
You don't have to but it is best to. If you aren't planning on reroofing at the same time you are going to have to remove existing shingles in order to tie in the new roof in the valleys anyways so you may as well.
About 2' above where the valleys will be is about what you want to remove, any more and its that much more material and labor you will need to tie everything back together. Any less and your butt ends are too close to the valley for my liking.