We live in a semiattached house with a cinderblock firewall separating
the homes. The roof is sheathed normally except for about 2 feet on
either side of the wall. There they used what looks like deep blue
papered sheetrock, not cementboard, to sheath the area directly over
the top of the
cinderblock wall with it essentially resting directly on the top of
the wall and then extended about 2 feet on either side of it.
They did a double layer of this material and then topped
that with sheathing and then of course roofing paper and shingles. As
I understand it this blue material is a firebreak to prevent a fire in
one side from traveling to the other.
When we had the roof replaced about 5 years ago they replaced the
original material which was destroyed by moisture and literally caving
in and it was assumed that was caused by a leaky roof. Not long after
the new roof went on we noticed water stains appearing along the edge
of the new material where it first meets the cinderblock wall along
practically the entire length of the wall. We called the roofer back
in to look it and he said it was caused by condensation traveling up
the cinderblock wall from the ground. I do see what appear to be
on side of quite a bit of the wall. He said little could be done about
it but sprayed expandable foam in the seam along the top edge of the
wall along the entire length of the wall on both our side and the
neighbors side. After that, for quite a while, I had not noticed any
new moisture so
we assumed it was fine.
Now 4 years later I am again seeing signs of new moisture.along this
same area. Not sure what to do from here. He claims the foam was
really the only thing he could do. My feeling is that if it is
condensation coming up the wall then to block it, it would mean
tearing the roof off the entire length of the firewall including the
blue board material and capping the cinderblock wall with some sort of
barrier before relaying new blue board and reroofing the area. Any
ideas if the condensation scenario is the plausible cause and/or
what is the best way to handle this problem?
Thanks in advance,
There are two key things to prevent condensation - prevent the surface
from getting below the dew point and remove the source of moisture.
have you noticed if this is a winter or summer situation?
is there any exposure from the house up to the attic that would allow
air to travel to where you're seeing the damage? This could be small
cracks or a space between the block wall and the sheet rock in your
Are your bathroom fans properly vented outside?
I had a situation in a rental property where the pipes kept freezing.
They ran through interior walls and seemed well protected from the
elements. We found that in the attic, there was an air gap between the
firewall between units and the inside walls. This allowed the cold air
to flow down the interior walls, into floor cavities and freeze pipes.
Something similar could be happening to you. The warm, moist air from
the house could be escaping through cracks and travelling up the
firewall and condensing on the cold underside of the roof and the fire
Another real possibility is the bathroom fans. Seems every unit I look
at has the fans vented into the attic spaces. Obviously, this will
just pump warm, moist air up into the attic, which will condense on
any cold surface. This is a big problem.
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