What does a vapor retarder do?

What does a vapor retarder do?

A vapor retarder is a material that reduces the rate at which water vapor can move through a material. The older term “vapor barrier” is still used even though “vapor retarder” is more accurate. The ability of a material to retard the diffusion of water vapor is measured in units known as “perms” or permeability.

What is vapor diffusion retarder?

A vapor barrier or vapor diffusion retarder is a material that reduces the rate at which water vapor can move through a material. The older term “vapor barrier” is still used even though “vapor diffusion retarder” is more accurate.

What is a good vapor retarder?

To be considered a vapor retarder, the material should have a permeance or “perm” rating less than 1.0 as tested in accordance with ASTM E-96. The lower the perm rating, the better the ability of the material to control the diffusion of water vapor.

What materials are considered Vapour retarder?

Materials used as vapor retarders:

  • Elastomeric coatings can provide a vapor barrier and water proofing with permeability ratings of .
  • Aluminum foil, 0.05 US perm (2.9 SI perm).
  • Paper-backed aluminum.
  • Asphalt or coal tar pitch, typically hot-applied to concrete roof decks along with reinforcement felts.

Should you put plastic between insulation and 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.

What is a good perm rating?

A perm rating of less than 0.1 is considered a Class I impermeable vapor retarder (which is also considered a vapor barrier); perm rating between 0.1 and 1 is considered a Class II semi-permeable vapor retarder; a perm rating between 1 and 10 is a Class III permeable vapor retarder; and a perm rating greater than 10 is …

What is concrete vapor retarder?

Vapor retarders are materials that will minimize the transmission of water vapor from the sub-slab support system into a concrete slab. Vapor retarders are typically specified according to ASTM E 1745 and have a permeance of less than 0.3 US perms (0.2 metric perms), when tested by ASTM E 96.

What is a vapor retarder in insulation?

A vapor retarder is defined as a material or system that adequately retards the transmission of water vapor under specific conditions. The kraft facing on insulation is a vapor retarder. It can reduce moisture movement through your walls, floors, and ceilings.

Is drywall a vapor retarder?

The permeance of unpainted drywall is very high, generally between 20 and 90, so it’s not a vapor retarder at all. Meanwhile, air leakage through a 1 square inch hole in a sheet of drywall allows 30 quarts of water vapor to pass through the drywall under the same conditions.

Is plywood a vapor retarder?

A kraft faced fiberglass batt is a Class II vapor retarder. Latex painted gypsum board (one coat of latex paint) is a Class III vapor retarder. Plywood sheathing and oriented strand board (OSB) have perm values of greater than 1 perm when using the wet cup test.

Is plywood vapor permeable?

OSB sheathing and plywood sheathing covered with a building paper or housewrap and vinyl siding are classed as vapor semi-permeable.

How do you attach vapor barrier to a wall?

Put up the wall plastic Stick the vapor barrier material to the foundation seal tape and then use mechanical fasteners to hold it forever. Drill holes through the plastic and through the seal tape into the block. If you drill through the seal tape you will prevent the plastic from peeling off when you remove the drill.

What is a Class 1 vapor retarder material?

Vapor Retarder. A vapor retarder is a material that has a permeance of 1.0 perm or less and greater than 0.1 perm. A vapor retarder is vapor semi-impermeable and is classified as a Class II vapor control layer.

Are vapor retarders necessary for basements and garages?

Although a vapor retarder or barrier isn’t required under slabs used for unheated garages and outbuildings, it is recommended. Moisture moving through a concrete slab into the building structure can cause dampness issues, and even cause metal sitting on the pad to corrode and stain the concrete.

Is latex paint a smart vapor retarder?

Latex or enamel paint qualify as Class III vapor retarders. Class III vapor retarders can be used on the interior side of the wall in the following climate zones in any of the conditions outlined. The IRC does not require or prohibit the use of vapor retarders in climate zones 1, 2, 3, and 4.