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Posted by Joe on February 4, 2007, 12:24 pm
> Few years back I looked in the attic and noticed that I'm getting
> frost on the roof decking above the shower in my bathroom. Only
> happens when its extremely cold out. Zero degrees, somewhere around
> there. Obviously what's happening is that moisture from the shower is
> rising, hitting the cold decking and collecting. The frost than melts
> and darkens the decking and trusses in this localized area above the
> shower.
>
> Originally, we were talking large patches of frost probably around the
> size of a standard shower stall. Heavy white. If you'd scratch it
> you would get snow. Figured that this couldn't be good
> so a couple years back hired a guy to take care of the problem. He
> installed these heavy-duty bathroom fans to suck out the moisture (and
> all the heat too). In addition, he put in a new light can in the
> shower stall that supposedly had a better seal. His theory had been
> that the moisture had been seeping through the fixture.
>
> Now I take a shower with the door to the bedroom open and we're moving
> the air so efficiently that the mirror fogs up at the top only and
> even then it's not bad. This helped my frost problem in the attic a
> little bit.
>
> The next year he installed ventilation in the attic to move the air up
> there. Unfortunately, don't know the correct lingo here. A small
> octagonal window at each end of the attic, and a heat register looking
> thing on the eaves. Again, helped a little bit.
>
> Last winter he suggested that we paint the shower ceiling with this
> special vapor barrier paint.
>
> Yesterday, Wisconsin was hit with frigid weather. Poked my head in
> the attic to see how we were doing. Sure enough, a faint swatch a
> foot by maybe two feet on the decking and a heavier one inch band
> following the upper edge of a truss all the way down to the eaves.
> This one is so white that you can not see the wood underneath. (Know
> these descriptions probably aren't helping much, but I do have digital
> pictures.)
>
> I guess my question is is it normal to have some heavy patches of
> frost on the roof decking above your shower in the dead of winter.
> Part of me says that no, I fear that over time the wood will rot and
> get punky and I definitely want to avoid a mold problem. But now
> another part of me is starting to wonder if this is normal to have
> frost above your shower stall in the dead of winter. I mean it's not
> like there's frost up there all winter long. Maybe a week. Maybe
> two. Don't think it's more than that. And this morning when I woke
> up there was frost on the windows and I think that's normal to a
> degree. And I'm getting so tired of throwing money at this thing. I
> can think of several other things I would like to purchase.
>
> If this isn't normal and must be fixed, now what? In addition to the
> work I mentioned above, I have been assured that I have a good vapor
> barrier between the bathroom and attic. The barrier is buried by
> something like a foot of those peanuts.
>
> Thank you for your time,
> Brian
Seems a shame to keep throwing all that nice warm moist air out into
your nasty Wisconsin weather. Just speculation, but could it instead
be recycled into the heating system via a small cold air return to the
furnace plenum? A competent HVAC engineer could help with pros and
cons on such an approach. This is being done with dryer vents these
days . HTH
Joe
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