2 years ago, I built a 18x22 workshop in my back yard in Colorado. It
basically goes unheated during the winter, except when I working in it
and I use a space heater. When I insulated the attic area, I placed
R-19 bats between the rafters directly on top of the ceiling boards.
My question is in regards to a vapor barrier. I don't know if its
necessary in this situation. If I remember correctly, the bats had a
paper backing and I did put that side down onto the ceiling boards.
If a vapor barrier is needed, what would be the best way to resolve
Building codes say that 6 mil PE should be stapled to the joists
before ceiling material is installed. Since that may not be possible,
coating the ceiling with an oil based primer and paint might work best
plus whatever caulking is needed. It could slow down the vapor
transmission enough to avoid problems in the attic/roof area like
condensation fueled mold development. Roof and soffit vents are
desirable, if possible. The simple paint barrier might be all you need
for the present.
Thanks for the advice. It would be a pain to staple PE to the joist
now. The ceiling and walls are OSB with 2" slats covering the
joints. I put three coats of latex paint on all surface. I may go
back and caulk everything. The attic has dormer vents on both ends
I would question the value of that procedure in this situation. The
point of that placement is to assure that moisture inside condenses
below the barrier, to keep the insulation dry. However:
-- in rlz's situation, occasional use as a workshop, I doubt there's
going to be much moisture inside to condense, unless he uses a
humidifier, or if his space heater is an unvented gas one.
-- any condensation in this location would get into the ceiling
material. Obviously you'd much rather have it in the ceiling than in
the insulation, but it's still a consideration.
Rob/rlz didn't mention whether he A/C-s the workshop in the summer.
Even Colorado can get damp in the summer, and A/C would cause outside
humidity to condense on top of the barrier--where the insulation is.
So I would say examine the attic under worst conditions, and if the
insulation feels damp, consider an additional barrier. Worst
conditions would be:
-- Cold outside with high relative humidity, using the workshop for a
long period of time with several people, a humidifier, or an unvented
gas heater inside.
-- Hot and moist outside, running A/C inside.
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