Frost on roof decking above shower
 

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

Frost on roof decking above shower
 

Frost on roof decking above shower
 

On Feb 4, 8:03 am, " wrote:
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

Frost on roof decking above shower
 

Should have mentioned that the exhaust fans that were installed
(expensive top-of-the line I'm told) are jetting the moisture not into
the attic but rather through a ribbed hose that goes directly
outside.

Frost on roof decking above shower