"Jetmech" wrote in message
...
On Mar 16, 5:57 pm, "Bob F" wrote:
"Jetmech" wrote in message

...

I noticed paint bubbling in my kitchen ceiling. I went into the attic
andfound alotof water underneath the tar paper vapour barrier as well
as on top of the tar paper, which must have been soaked trough. The
insulation is opnlywet where it meets the vapourbarrier. What the
hell is going on here. I've about 50 sq feet of dammage plaster
celing.

My understanding is that tar paper is a moisture barrier, not a vapor
barrier -
that is, it allows vapor to pass through it. So, the vapor in your house
passes
through it, then condenses in the insulation. It is possible a vapor barrier
paint could help.
Otherwise, install a proper vapor barrier in the attic under the insulation,
or
install insulation with a built in vapor barrier.

Theres no venting from anything in the attic. The exhaust from the
Microwave is 6 inch galvanized insulated pipe. It's blowing into a
lot of snow and has melted a large patch. The damage area in the
attic is about 50 sq ft. It is also above the portion of the kitchen
where all the cooking is done. i.e the stove is there, kettles, etc.
I do have a humidified house that is automatically controlled. At -10
C I think I'm around 29% relatice humidity. Could this be as was
mentioned, moisture going through the tar paper? Would 6 mil plastic
be better? Does that much moisture actually travel through the
celing? Right now I'v removed the damaged insulation in the hopes of
the ceiling drying out.

According to
http://www.bpa.gov/energy/n/energy_T...porbarrier.cfm
that would work.

It doesn't take much moisture getting through to add up over time, as very
little evaporates in the cold temps.

Obviously, leakage has to be dealt with separately.