I have an old barn that I’d like to fix up for a workshop. I was planning to sheath the frame with plywood or SIPs, then reattach the old vertical board siding. However, I’m concerned that water might get in between the old siding and the new plywood or OSB, causing both to rot. (The siding is not at all waterproof, what with knot holes, cracks, and gaps between boards.) My understanding is that wood can get wet without rotting as long as it is allowed to dry out again later. The old siding has been exposed to air on both sides, and so has lasted 100 years. But now it will only be exposed on one side. I would hate to lose the boards that give this barn so much character. (I would also hate to lose the new plywood or OSB...)

Is it okay to just nail the old siding directly over the plywood? Would housewrap help to protect either the old siding or the new plywood? Should I use furring strips? If the furring strips were installed horizontally, it seems that they would form pockets to hold water. The strips could also be installed vertically, like a board-and-batten wall, with the battens on the inside. This would form little vertical air passages, which should allow air to circulate behind the siding. But this might also make little chimneys, which could cause a fire to spread quickly up the wall, if a fire were to ever start.

What’s your recommendation? Surely I’m not the first one to come across this problem. Any help that you could give me would be greatly appreciated.

Thank you very much.

--Bruce Brittain