We are building a new house and are getting ready to install the drywall on the ceilings. We have installed a 6 mil plastic barrier on the underside of the rafters to act as an air & moisture barrier. The barrier will be sandwiched between the drywall and the rafters and under the blow-in insulation. I talked with another insulation guy that said he thinks it might trap moisture in the house and cause problems with the ceilings. He thinks we should tear out the plastic before we install the drywall ceilings.
Does anyone know if the plastic barrier will help or hurt us?
Best Answer
It depends on your local climate.
For climates that are higher humidity inside than outside in summer (a dry climate) plastic on the interior is OK. For climates that are higher humidity outside during the summer (a humid climate) plastic on the interior could be a serious mistake.
Here is a link to a good brief discussion titled, "What happens when you put a plastic vapor barrier in your wall?":
http://www.energyvanguard.com/blog-building-science-HERS-BPI/bid/75130/What-Happens-When-You-Put-a-Plastic-Vapor-Barrier-in-Your-Wall
If you have very cold winters in your area without very high summer humidity, then a vapor barrier near the inside will help keep your insulation dry when it is cold outside and your house is relatively warm and humid, otherwise take the plastic out.