David writes from Normalville, Pennsylvania: "Our cathedral ceilings rafters are constructed with 2X6's we have installed the rafter-mate ventilation product and insulated with Kraft faced insulation (R-19 Compressed) facing the living space. The ceilings will be covered with 3/4" Red Oak v-joint wood. Would it be better to install a vapor barrier over the Kraft facing or do you think the fan fold product would act an additional vapor barrier and add more R-value to the ceilings?"

Answer: Kraft paper is a vapor retarder and we do not recommend an additional vapor retarder in the application you describe. Fan Fold insulation will not act a vapor retarder but will help with air infiltration and add little additional R-value.