Ok, this is about as basic as it gets, but I still have to ask. I have 1/2" sheathing, 15 lb felt, and comp shingles. The shortest roofing nails I can find are 1". Won't this poke through the sheathing? None of the existing nails poke through. Thanks.
Yes the nails will, and should, poke through the sheathing. In fact, they should come through about 1/4" this is what stops them from backing out. I always use 1-1/4" just because I find them easier to drive with less hitting of the fingers.
What type of roofing was on there originally? It's possible the previous roofer used 3/4" nails, they are available, but even with these you should be able to see the points on the inside. Read the shingle package, some manufacturers require the nails to come through 1/4"