Exterior Wall Vapor Barriers

Vapor barriers are sheets of plastic or other material placed on one side of insulation sheets.

Exterior wall vapor barriers.

Vapor barriers are used to stop water vapor a gas from entering a wall cavity where it can turn into liquid water if the water vapor contacts a cool or cold surface. When a vapor barrier is on the side of a wall where the dry air is i e outside in winter or inside in summer moisture problems can occur. A vapor barrier s job is to keep water vapor in humid air from diffusing through one side of a wall and finding a cool surface inside the wall. Below grade walls and floor slabs transmit ground moisture through concrete walls or slabs.

If you are adding an exterior wall anywhere in the house and you answered yes to either of the above questions you should consider using a vapor retarder. If this happens and the water can t evaporate rapidly back into a gas wood rot mold and mildew become a reality. A vapor barrier reduces the movement of water vapor by. 2010 2013 ashrae 90 1.

Massachusetts energy code 780 cmr. Where is the wall located. And the canadian national. Very hot and humid climates may benefit from an exterior vapor barrier that keeps outside humidity from penetrating into walls.

This wall assembly will dry from the vapor barrier inwards and will dry from the vapor barrier outwards. Window door openings connect both walls with 1 2 underlayment plywood and are sealed to the vapor retarder air barrier. To thwart the comments of the expense of the double wall headed my way i would like to add that the second wall that i add to the interior is totally non structural 24 o c. The few holes in this barrier required for exterior lights switches can be easily sealed with a can of foam or silicone mushroomed on both sides of the vapor barrier.

All have been evaluated by the air barrier association of america abaa and meet the most stringent energy codes including. A vapor barrier against the concrete surface is generally recommended before wood framing or flooring materials are installed. The standard installation of a plastic vapor barrier is between the studs and the drywall but there are some exceptions to this. This is then followed by a 2x4 wall with studs offset from exterior wall another 3 1 2 fiberglass or rockwool then sheetrock.

Vapor retarder use and placement. In certain climates vapor retarders can be a vital part of the wall construction. This barrier is meant to keep moisture from getting to the insulation in the walls and ceilings and it is required by building codes when insulating most houses. In any case the vapor barrier must point to the warm side.

In hot climates any moisture that condenses on the exterior side of the vapor barrier will be drained to the exterior since the vapor barrier is also a drainage plane. 2012 2015 iecc.