I was wondering if someone could enlighten me. In all that I've read about
bathroom exhausts, most of the time it talks about using the soffit to
exhaust the vapour.
However, I talked to a friend and he said to avoid that, because it builds
moisture under the endge of the roof. I'd be better off with a roof vent.
Could someone please give me some feedback on this?
I just replaced mine from a 50 cfm to 130 cfm vented it to the soffit where
there was a vent, however before I did this I started to notice roofs in the
neighborhood looking for roof vents, can't say that I seen any. Thats not
saying that the soffit is the best.If the roof vent is best, there not that
expensive, why are there not more of them out there.
When I re-roof I'll look where mine is vented to see if there is any mold or
It is good practice to hide vents by putting them on roof at the back of the
house, where they are more or less invisible from the street. This may (or
may not) be why you can't see vents from the street.
Do you have existing roof vents? If so you can route your vent
hose to the edge of an existing vent and staple it in place. This
allows most of the exhaust to escape and still allows the roof vent
to function as originally designed.
I assume this method is not to code but, I have used this method for
more five years now without any moisture damage to any part of the
vent area or the roof.
First never exhaust a bath vent to the soffit area. The natural air
flow will keep it from going out the soffit and you will just build up
moisture in your attic. Not good
I suggest you avoid venting it through the soffit. In this case since
the natural flow of air is from the soffit to the higher roof vents it will
tend to get sucked into the nearest soffit vent and cause the same problem,
but to a lesser degree.
If your neighborhood is like mine, most of the houses were built by the same
developer around the same time. As such they all share certain details. In
my case most single story houses vent through the roof as well as second
story baths but first story baths vent through the wall. Some baths with
windows have no vent at all.
I think the preferred method it to do whatever is easiest and still satisfy
code which says the vent must be a certain distance from any window or door
openings (this may also include soffit vent openings but I am not sure) and
a certain distance from property line. (sorry I don't recall that distance).
I believe back draft prevention device is also required (a flap)
Regardless of location, install vent pipe all the way to the outside.
Natual air flow??? What kind of air flow do you think you have coming
from the soffits to the roof line? Wind tunner perhaps? Not.
Soffit vents are generally (I am saying generally from the ones I have
seen) are a few feet apart. They are suppose to help with heat
in the summer and keeping the roof cold in the winter so water doesnt
prematurely melt and create an ice backup. (ice dam)
That being said, putting a 6" hole in the soffit isnt going to disrupt
The forced air from the fan will blow the exhaust right out the vent.
or less a few feet away. The 'Natural Flow" of the soffit doesnt even
come close to making a measureable vacume effect that would suck in the
exhaust from the vent in the soffit.
One thing that can also bit people in the butt is that when venting
warm air vertically, you increase the chance of condensation flowing
in from the vent. Lots of insulation would be advisable. (not sure if
a warm climate or cold)
Horizon. runs you can pitch so that the flow wont come back.
Just a thought...
P.S.... I personally HATE putting holes in the room. More holes, more
water coming in. Over the years, the moisture from the showers and
from the vent cause some crappy looking roofs too (stains)
Here's one other possibility that I did: Our second floor bathroom
happens to be directly under an attic dormer. I ran the fan exhaust a
couple feet to the side to be directly under the dormer wall, and then
up a few feet into the dormer wall. It vents out the side of the
dormer wall. Seems to be the best combination to me, that the vent
pipe rises continuously, and then vents out the wall with no roof
AND out the ridge vents, which you must have for all the reasons mentioned.
In winter especially the relative humidity of the vented air drops
dramatically. Even in summer with humid outside air, if it isn't
raining in your attic, the fan exhause won't start it.
Lots of insulation would be advisable. (not sure
I disagree. Insulation does not add heat. It is a barrier that
prevents heat flow. Your insulation layer is what divides "inside" from
"outside". Your attic should be outside so the insulation must be
on/under the attic floor. That insulation will not affect far exhaust
into the attic.
And in-between it will leave moisture in the attic. Not good!
We are talking about a bathroom fan.
I believe you snipped a little too much and lost the context.
"One thing that can also bit people in the butt is that when venting
moist warm air vertically, you increase the chance of condensation flowing
back in from the vent. Lots of insulation would be advisable."
So it appears Bocestb was suggesting insulation around the duct to keep
it warm (not add heat as it would already be warm) to reduce condensation.
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