"JoeSpareBedroom" wrote
The previous owners of my home routed the flex duct from the bathroom fan
right to the underside of a normal roof vent and sort of wired it in
place. I'm about to re-roof the house, and although I'm tending away from
this idea, an acquaintance comes highly recommended for this kind of
work. Three person crew, all permanent people. But, while looking at the
roof with him today, he gave me a blank stare when I mentioned a vent
specifically for fans. Can anyone describe what these things look like?

Yes, I have two estimates from "real", insured companies. :-)

There is a "special" type vent for kitchen/baths, it has a flap to
open/close. The part I'm not sold on is, I feel a bath exhaust does not put
enough pressure to push open all the time. Another thought crossed my mind
about them is, hornets/wasps love to build nests where it is warm (any
roofer will tell you about the nests found in vents torn off). Anyways, if
wasps or whatever builds a nest at the flap, it would be possible the flap
will never open. Here is a link some what similar to what I installed
(once). Although I know I didn't pay anywhere near what this place wants.
http://tinyurl.com/g86rm

A long time ago I seen a set up which I thought was pretty slick, and used
it when I used to be in contracting. I had run across the set up numerous
times throughout the years during tear-offs.

A normal roofing vent is used, pick your choice for sloped back/square etc.
http://tinyurl.com/z8pdf
A 3" hole is cut in the sheathing, before any felt paper/shingles are laid
(can be done afterwards, I just found it easier to do if had power to
replace sheathing etc), a 18-24" piece of galvanized duct work is
installed, the roofer cuts 3 slots in one end of the duct, approx 3" down
the length, then fold these outwards, drop the remaining of duct into the
hole, then fasten the fins to sheathing. From there, run flexible duct to
the exhaust fan. You _MUST_ have the flex pipe form a trap, especially if
you live in cold weather areas. Otherwise you will get condensation run
back into your exhaust fan. Do _not_ use all galvanized rigid duct back to
your fan, you will get a fan that drips condensation.

*NOTE* Make sure if the roofers cut a hole before they felt/shingle, they
don't cover up the hole up with roofing material, otherwise as you know,
you'll have an exhaust that leads to sheathing failure.

Sorry for being so winded.