My house has a separate building in the back with plywood T1 siding on it. Most of the siding is in ok condition. Some of the siding is rotten where the deck, now removed, used to be attached. The bottom part (below where the deck used to be) doesn't have any siding, and what's left of the sheathing under it is in bad shape.
It looks like this:
I'm planning to shingle the building so it matches the main house.
What I'm thinking: put new sheathing up everywhere, then paper and shingles.
My question: do I need to remove all the existing siding first, or can I attach the new sheathing to it? Of course I'll remove the rotten siding, but some of it is in good shape, and because of the way the wall is build, having the extra thickness of siding would actually help.