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. :-)
Check out your Home Center, in the heating and ventilating department, you
will find a number of different types of roof vents. Or check the web site
of the company that makes the fans, e.g.: Broan, and you will see what they
make in different sizes, shapes and types.
They are kind of hard to describe, but basically what you want is a
galvanized roof cap for a bathroom fan. There is a picture of one here
In my experience, go to a small hardware store, home depot only has
one or two kinds, and the small hardware may have several different
kinds that willl suit your application. Another option is to use a pvc
pipe and plumbing vent stack flashing, but the pvc pipe will need a
trap, or a J bend at the top to prevent water from coming back into the
The others have told you want you want.
Give some thought as to where on the roof to place it. Generally speaking,
the HIGHER on the roof you make the holes the less likely water is to leak
in. And if you have it high on the roof if often doesn't make much
difference which side of the ridge it's on. If you don't care which side
then put it opposite the side the BIG WINDS come.
Once you decide what you want, I suggest you buy it yourself and make it a
part of the contract for the roofer to install it. It usually isn't a big
deal to install it after the fact but you have guys on the roof anyway so
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.
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.
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.
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