- Q.I am residing an old house
that is uninsulated. I plan to add foam exterior
sheathing and blown-in cellulose in the walls. Is a
vapor-retarding paint adequate to prevent moisture
problems in the wall?
A.Two coats of a latex
vapor-retarding paint or an oil-based enamel will
provide reasonable protection against moisture
diffusion into the wall. But diffusion is often not
the problem. The most important thing is to seal
the wall as much as possible to prevent interior
air from infiltrating the wall cavity. This will
involve sealing the baseboards to the floor and
wall and around electrical boxes, windows, doors,
and other penetrations.
If you add 1/2-inch foam, the inside surface of
the sheathing could get cold enough to reach the
dew point. The foam sheathing you add should be at
least 3/4 inch thick, and preferably, 1 inch thick.
This would provide enough insulation so that the
dew point in the wall section would be in the foam
and not closer inside where it might cause