Insulating a Roof
Q: For the last four years, my wife and I have been building a house. She decided on open beam ceilings in the living room, so we put up insulation. But, before we could put up the Sheetrock, winter came. From the heat and the cold mixing, we have condensation between the insulation and the roof. If I put the Sheetrock up, will that stop the dripping, or do I need roof vents?
—Sean, Corbett, Ore.
A: Tom Silva replies: When insulating any roof, you need an air space of at least two inches between the underside of the roof sheathing and the top of insulation. Proper vents can be stapled to the roof sheathing to create an uninterrupted airflow. The soffit and ridge should also have venting. Install a good vapor barrier under the insulation—on the warm side—making sure there are no holes. Any seams, if needed, should be overlapped by at least 16 inches. Foil taping or polyurethane caulking the seams won't hurt. The insulation should be R-30. (R-value refers to a material's ability to resist the transfer of heat. The higher the R-value, the more insulating power the material has. ) Make sure you don't compress the insulation, which makes it less effective, if it doesn't fit correctly in the space. Cut a new piece instead.