When installing skylights in our living room in Atlanta, Ga., we discovered some rot that led to us having to demo and reframe around our fireplace. I’m happy to say we passed our framing inspection. For the future insulation inspection, the inspector told us that he wants to see a vapor barrier on the mineral wool we used in the chimney chase. There was no insulation in the chase before, and we decided to go with mineral wool over fiberglass-batt insulation (which can come with its own integrated vapor barrier). My question is, what should we use for the vapor barrier inside the chimney chase?
—ANNA via email
Green Building Advisor editor Martin Holladay responds: Your inspector is wrong. There is no code requirement in your climate zone (zone 3) for walls to have an interior vapor retarder, much less an interior vapor barrier. Building codes sometimes require an interior vapor retarder, but only in zones 5 and colder.
While there is no need for a vapor barrier, you certainly need an air barrier in this location. The best air-barrier material in this case would be 1⁄2-in. drywall with taped seams. For more information on the need for air barriers behind metal fireplaces, visit this useful web page from the U.S. Department of Energy: basc.pnnl.gov/resourceguides/walls-behind-fireplaces.
From Fine Homebuilding #285