Exterior Wall Vapor Barriers

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.

Exterior wall vapor barriers.

Massachusetts energy code 780 cmr. Window door openings connect both walls with 1 2 underlayment plywood and are sealed to the vapor retarder air barrier. Vapor barriers are sheets of plastic or other material placed on one side of insulation sheets. Below grade walls and floor slabs transmit ground moisture through concrete walls or slabs.

Where is the wall located. The standard installation of a plastic vapor barrier is between the studs and the drywall but there are some exceptions to this. 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. 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.

In certain climates vapor retarders can be a vital part of the wall construction. This wall assembly will dry from the vapor barrier inwards and will dry from the vapor barrier outwards. If this happens and the water can t evaporate rapidly back into a gas wood rot mold and mildew become a reality. In any case the vapor barrier must point to the warm side.

Very hot and humid climates may benefit from an exterior vapor barrier that keeps outside humidity from penetrating into walls. 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. All have been evaluated by the air barrier association of america abaa and meet the most stringent energy codes including. 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.

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. 2012 2015 iecc. 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. And the canadian national.

2010 2013 ashrae 90 1. A vapor barrier against the concrete surface is generally recommended before wood framing or flooring materials are installed. A vapor barrier reduces the movement of water vapor by. 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.

Ccw provides three types of air barriers. This is then followed by a 2x4 wall with studs offset from exterior wall another 3 1 2 fiberglass or rockwool then sheetrock.