the epinasty conclusion

[Jean-Joseph Cote]

>Is anyone on the list a roofer?

Certainly not a professional roofer, though I've done a little bit. 
Those who haven't done any roofing should be aware that "felt" in this
context doesn't refer to the pressed wool stuff that you use to make
fedoras, hand puppets and yurts, but is rather the industry term for
something that would be colloquially called "tarpaper".  Typical roof
construction these days has plywood nailed to the rafters, followed by a
layer of roofing felt, with the strips (4' wide) overlapping and glued
together with roofing cement (aka roofing tar, aka sticky black glop). 
Then the shingles go on top of that.  When you redo the roof, you can
just nail a second layer of shingles on top of the old ones, and maybe
even a third, though some prefer to always strip back to the plywood when
putting on new shingles.  I've never seen anybody put felt on top of
shingles, under the second layer, but I'm no expert in these matters.

Jean-Joseph