Do you need vapor barrier with batt insulation?

Fiberglass batts, the insulation found in most houses in the U.S., are inexpensive and quick to install. Like other batt-type insulation, fiberglass has a predictable R-value if not compressed but is difficult to fit around obstacles without leaving gaps. In most climates, it needs a vapor barrier.

Do I really need a vapor barrier?

Vapor barriers protect against mold and rot inside structures by preventing condensation and moisture from building up and damaging building materials. If a home is being built in a very humid climate, a vapor barrier can be an essential source of protection from problems caused by excess moisture.

Are vapor barriers required by code?

The International Residential Code (IRC) requires either a Class I or II vapor retarder on the interior side of frame walls in climate zones: 5, 6, 7, 8 and marine 4 (see climate zone map).

Does closed cell spray foam act as a vapor barrier?

While both materials can be used as an air barrier (open cell at 3.75” thickness or greater and closed cell at 1” thickness or greater), only closed cell spray foam creates a fully sealed system that can be used as an air and vapor barrier (at 1.5” thickness or greater).

Do I need a vapor barrier behind drywall?

Normally interior walls do not require a vapor barrier, but there are some situations where it is highly recommended. A continuous plastic vapor barrier behind the drywall will protect the interior walls of these areas from water damage.

Does Rockwool insulation require a vapor barrier?

Mineral wool typically doesn’t require a vapor barrier. Its high-density level allows it to absorb moisture before it has a chance to penetrate the interior walls of the foundation.

Does drywall act as a vapor barrier?

Drywall is a decent air barrier but not a moisture barrier. In cold climates, vapor barriers (such as polyethylene) should be installed between the drywall and the insulation because the interior tends to be more humid than the outdoors. Plywood/OSB sheathing under the siding forms a decent air barrier, too.

Can rigid foam be used as a vapor barrier?

Rigid insulation has an R-value of up to 6.5 per inch, but it also can be an effective vapor retarder. Rigid foam board, especially foil-faced polyisocyanurate, creates a vapor-impermeable barrier, so the wall would have limited drying potential.