I just got back from a week in Martha’s Vineyard replacing 720s.f. of a 1240s.f. barn roof and doing some misc. repair work. Wood plank and beam, shingles. I had to rip off the old shingles, felt, and replace some of the OSB on the top layer of the stress-skin panels underneath, fascia boards, etc. Everything had water damage and rot because the previous contractor never installed any space for airflow between the shingles and roof deck.