"But Ive never seen them in a modern chimney with a clay or metal flu."


As a former mason, I would have to say that the inside of a flu liner is pretty slick, but it depends on who layed the flu as to wether bats can perch on the inside. Some dont clean the inside joints as good as others. Must have something to do with watching over their shoulder for immigration authorities. Also sometimes it is necessary to "rack" a flu one way or another, to miss floor joists, trusses etc.. You cant see it from the outside, if done properly it will create a bunch of tiny ledges, sometimes a couple of big ledges if not so proper. Flashing a chimney to prevent water, bugs, and bats is an art form and requires a masonry saw, patience, and very little caulk.

The underlayment is some sort of titanium film from what I've been told. No way a bat can get past it. lol I still be they left a gap somewhere.

I'm working on two different houses with steel "shake" roofing. Following the evidence(guano) I removed the peak cap and found the peak vent completely open. Plenty of room under the cap and plenty of evidence of bat activity there. Bats only needed to find a way under the steel and they were in the building.

interwrap udl.............

Vinke, that's probably the stuff. I don't see it being installed good enough to keep bats out though.

In my experience, bats can't climb or hold onto flue tile (by the way, "flu" is a respiratory disease. A flue is part of a chimney). Can't fly up and down a chimney either, unless it's HUGE.