Q. When insulating an old New England farmhouse, it was not practical to install a vapor varrier onto the ceiling below and attic. We filled the joist spaces with loose fiber-glass insulation and rolled down unfaced batting above that -- about 16 inches in all. Although the attic is well ventilated, I am concerned about moisture getting trapped in the insulation and timbers, thereby cutting down the effectiveness of the insulation and possibly causing damage to the wood. The oil- base ceiling paint has started to flake off the old plaster. My paint supplier thinks this might be attributed to a residue of calcimine in the plaster. What paint will make the ceiling plaster vaporproof? John Mckee Brunswick, Maine
A. A veteran insulation contractor believes that if the attic indeed is well insulated, the lack of a vapor barrier below the insulation is of no particular consequence.
Be sure, therefore, that mechanical or natural attic cross-ventilation occurs in all seasons. Eliminate any roof leaks that might drop moisture into the insulation from above.
Our painting consultant believes there may be little logic in attempting to stop moisture migration through the ceiling from below by putting on a coat of paint on the under part of the ceiling plaster. Some specialists do reccommend such a practice, however.
As noted above, moisture should be prevented from getting into the insulation from above; that is, in the attic.
To determine the cause and cure of the chipping-paint problem, send samples of the peeling paint to a paint manufacturer to see whether moisture or calcimine is the problem.
Generally, an oil-base paint is used on exteriors to prevent vapor from migrating through the outside walls.