Exterior Wall Vapour Barrier

Frame wall with cavity insulation and brick or stone veneer.

Exterior wall vapour barrier.

Above grade exterior walls with semipermeable exterior finishes like brick over oriented strand board sheathing require the placement of an additional vapor barrier on the exterior side of the. A vapour barrier is an important component in building construction. Its purpose is to help prevent water vapour from reaching building walls ceilings attics crawlspaces or roofs where it can condense and cause building materials to rot or grow mould. Below grade walls and floor slabs transmit ground moisture through concrete walls or slabs.

Finished basements often receive a vapor barrier layer between the concrete and the floor treatment to prevent damage from heavy rains or other moisture seepage. Building codes usually require a vapor barrier 4 mil plastic sheeting on exterior basement walls if the framing is attached to masonry or concrete surfaces or if the wood framing butts up against the outer basement walls. 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. Vapor barriers are applied to the interior walls in climates which are predominantly cold while they are best applied to exterior wells in predominantly hot climates.

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. This wall assembly will dry from the vapor barrier inwards and will dry from the vapor barrier outwards. A vapor barrier against the concrete surface is generally recommended before wood framing or flooring materials are installed.

Whether or not you need a vapor retarder hinges on three main factors your climate your home and the location of the wall you re insulating. 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. 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. It combines the superior air and water resistance vapor permeability and strength of tyvek with a vertically grooved surface to help channel water safely to the outside.

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