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Q.
We are putting in R-38 fiberglass batt insulation between engineered trusses in
a barn. Can we just put up wallboard when the insulation is up (paper on one
side, otherwise it is unwrapped) or do we need some type of vapor barrier?
A.
If the paper on the
insulation batts is just paper and does not have a plastic or tar component,
then you should add a vapor barrier. After all of the insulation is in place,
staple 4 mil or 6 mil plastic over the entire wall or ceiling. Where you have
electrical boxes, just cut an “x” in the plastic, corner to corner over the
box.
The vapor barrier is to keep the warm moist air that is on the inside of the
structure from migrating through the insulation to find colder surfaces. There
it would tend to condense and could cause mold to grow in the walls, or in
extreme conditions could cause rot.
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