I have a 960 square foot un-insulated hobby shop that was originally a flat
roofed foundry constructed of cinder block. Years ago I put a regular
peaked roof on the building rather than repair the flat roof. We have just
started framing in and insulating the inside of the shop with moisture
resistant Fibre Batt insulation and plastic vapor barrier and the plastic
vapor barrier is glued to every beam with beads of caulking compound to
insure a good seal.
It's been very humid here for the last week and my problem is we now have
moisture dripping down the inside of the vapor barrier. I'm getting all
kinds of different and conflicting advise including the option of applying
tar paper on the block wall before framing and insulating the wall. I also
know that the residential building code in my area requires venting that
runs from the wall cavity up to the attic but in this case trying to cut and
run vents up through the flat roof of this old building into the roof cavity
would be a massive undertaking. The way I look at it if the building still
had a flat roof and venting was not possible there must be an accepable and
code legal way of eliminating all the moisture build up.
Any help will be appreciated
Thanks in advance
Our local code doesn't require venting from wall cavity to the attic (don't
know what I was thinking) I was thinking about the plastic vents we
installed in the attic to allow air flow up from the soffet and facia.
Well, running a dehumidifier will work, until you come up with
a better idea, but if the indoor temperature is cooler than
the outdoor temperature, and it's humid out, then any air coming
in is going to drop water SOMEWHERE. Best I can think of
is to limit air infiltration, and try to control where
vapor barrier is only a good idea in areas that have A/C or a dehumidifier,
otherwise vapor barrier no good
either house has to breathe, or else be dehumidified some way
or else, you could always just move to Arizona
I stand to be corrected but if the moisture is behind the sealed vapor
barrier it has to be coming through the block walls of my shop. A
dehumidifier only removes moisture from inside the building not water on the
inside of a wall covered with vapor barrier and drywall. As far as not
installing a vapor barrier that's not an option because those of us living
in the North know that a vapor barrier is a must if you want to cut heating
bills and protect your building from rot and fungus.
If I understand you correctly, the condensation is on the outdoor side of
the vapor barrier, and only on the walls.
It seems like there must be a higher than normal moisture content in the
block walls, because I can't believe
that enough airborne humidity can go thru the block wall and insulation and
still hit a dewpoint on the barrier.
My first guess, especially if the problem is not all that uniform along the
walls, is that relatively large amounts of water are making their way into
the interior of the block wall, and subsequently soaking the cement. In
effect, you would be storing water in the hollows of the blocks. Any chance
their is a leak somewhere into the old flat roof parapets, scuppers, etc?
Are parts of the walls below grade?
The building is sitting on a poured concrete pad and none of brick is below
grade. The new peaked roof over hangs the old flat roof and all the
eavestrough are in good shape but one of the down spouts is very close to
the foundation of the building. You have got me wondering if the slab is
picking up a lot of water and that water is being drawn up into the block
wall. If thats not one of the causes does anyone think the fact that we
have had about 6 days where the relative humidity has been around 85% to
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