Choreboy wrote:

I was amazed to discover only wood under the shingles of my house, which
was redone about fifteen years ago.

Were they cedar shingles? The Cedar Shake and Shingle Bureau says felt
isn't usually used for shingles.

"Although not commonly used, a breather-type underlayment, such as
roofing felt, may be applied over either solid or spaced sheathing."