Are there drawbacks to using a second vapor retarder?
Matthew writes from Bernard, Maine: “I recently insulated my house walls with faced R21. There is an open kneewall behind one wall that is ventilated. I had to piece together a lot because of the variance in the walls. There is an area where I think there will be a draft. After reading the “can I add an extra vapor barrier question”, I wondered if that would be a good solution to reducing this draft. Are there drawbacks to using a second barrier? I don’t want to regret this in a couple of years.” Answer: Two vapor retarders can only be used when they are in direct contact with each other. Otherwise, you risk trapping vapor within the insulation pack at the second vapor retarder. Air infiltration can also be reduced using caulk at all construction seams and foam insulation in larger openings.
