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jack b
Gone Fishing
Premium,MVM
join:2000-09-08
Cape Cod
kudos:1
reply to SuperNet9

Re: Condensation on Attic fan, normal??

Depending on the type of construction, and local codes may be different, at a minimum you should have 1 sq.ft of vent opening area for every 300 sq.ft of attic floor area. More is better.

If vents are inadequate or blocked, moisture vapor can't escape readily enough and can condense on cold surfaces.

One thing to look at is it's possible there is heated air leakage into the attic from the living space.

Check any plumbing vent or chimney pipe chases for a good seal. If you have pull down attic stairs, make sure it's properly weatherstripped.
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mattmag
Premium,ExMod 2000-03
join:2000-04-09
NW Illinois
kudos:3
said by jack b:

One thing to look at is it's possible there is heated air leakage into the attic from the living space.

OK, I'm gonna dive into this a little and ask--- When did this become such a hot-button problem? I realize the issue, just playing devil's advocate a bit, because for decades it was pretty much standard-fare for bathroom vent fans to simply dump into the attic space. Most "older" carpenters etc that you ask about it will agree, and most also say they never saw damaging effects from the old practice.

itguy05

join:2005-06-17
Carlisle, PA
said by mattmag:

said by jack b:

One thing to look at is it's possible there is heated air leakage into the attic from the living space.

OK, I'm gonna dive into this a little and ask--- When did this become such a hot-button problem? I realize the issue, just playing devil's advocate a bit, because for decades it was pretty much standard-fare for bathroom vent fans to simply dump into the attic space. Most "older" carpenters etc that you ask about it will agree, and most also say they never saw damaging effects from the old practice.

Same here. We moved into our previous house in 2000. The inspector noted the bathroom fan discharged right into the attic. Said we should fix it because of mold. In 2012 when we sold it, I fixed it and put the vent through the side of the house. Total attic mold - 0. Nothing, nada. Beams and insulation were fine.


Msradell
P.E.
Premium
join:2008-12-25
Louisville, KY
reply to mattmag
said by mattmag:

OK, I'm gonna dive into this a little and ask--- When did this become such a hot-button problem? I realize the issue, just playing devil's advocate a bit, because for decades it was pretty much standard-fare for bathroom vent fans to simply dump into the attic space. Most "older" carpenters etc that you ask about it will agree, and most also say they never saw damaging effects from the old practice.

I'm not sure where you are getting this information from. It's against most building codes and certainly a bad practice to have exhaust fans vent into the attic. They should vent directly to the outside.


Draiman
Let me see those devil horns in the sky

join:2012-06-01
Kill Devil Hills, NC
Reviews:
·Verizon FiOS
said by Msradell:

said by mattmag:

OK, I'm gonna dive into this a little and ask--- When did this become such a hot-button problem? I realize the issue, just playing devil's advocate a bit, because for decades it was pretty much standard-fare for bathroom vent fans to simply dump into the attic space. Most "older" carpenters etc that you ask about it will agree, and most also say they never saw damaging effects from the old practice.

I'm not sure where you are getting this information from. It's against most building codes and certainly a bad practice to have exhaust fans vent into the attic. They should vent directly to the outside.

You mean it's against CURRENT building codes? I'm sure at one point it was was well within code.
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Red_Menace
poking around since 1978

join:2001-11-03
Littleton, CO
reply to mattmag
Code and old standards aside, the question was about condensation. Moisture in warmer air leaked (or sent) into a cooler attic will condense on the colder parts (such as a metal fan housing) if it isn't vented properly, that is all.