Bruce writes from Pine Plains, New York: "I purchased R38 $500.00 of faced insulation from Lowe's in Kingston New York, the contractor tech in the store advised me it was OK to use the faced insulation on top of the beams and insulation that was there already. This did not seam correct but he stated that was OK to do. After I started this project I felt this was wrong! I search for information and found in Owens Corning energy saving paper work it states…. (USE UNFACED OVER ADDING TO EXISTING INSULATION IN THE ATTIC). What do I do NOW?????"

Answer: As you accurately noted, when insulating on top of existing insulation we recommend using unfaced insulation so no vapor retarder will be on top of the original insulation. However, insulation with a vapor retarder can be placed up to one-third of the total thermal resistance in the assembly starting from the warm side. If the insulation you are adding has at least twice the R-value of the insulation already in place, then it should work. The other options are to remove the vapor retarder from the new insulation you will be placing on top of the existing insulation (messy and not really recommended) or freely slashing the new vapor retarder with a utility knife.