Exterior Wall Moisture Barrier

This wall assembly will dry from the vapor barrier inwards and will dry from the vapor barrier outwards.

Exterior wall moisture barrier.

Some moisture barriers for this application combine a foam strip with a waterproofing membrane that covers the bottom of the plate as well as the joint between the foundation and the exterior of. The exterior face of the wall or floor cavity should remain permeable in order to allow dissipation of any moisture that does enter the wall cavity. Not every wall does. In exterior walls that are below grade like basement walls.

Either design strategy can be applied to load bearing or non load bearing walls. 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. If water vapor diffuses or infiltrates into the wall cavity and finds the cool surface moisture problems can occur. A vertically grooved surface provides added protection against water by enhancing drainage away from the wall assembly.

Vapor barriers are sheets of plastic or other material placed on one side of insulation sheets. After the insulation is in place you will want to add a vapor retarder sometimes called a vapor barrier if you need one. The standard installation of a plastic vapor barrier is between the studs and the drywall but there are some exceptions to this. In any case the vapor barrier must point to the warm side.

Of course you can have moisure problems here even without the exterior vapor barrier because of what bill rose calls the rule of material wetting. In designing exterior wall systems moisture infiltration is controlled following two basic design concepts or strategies. Very hot and humid climates may benefit from an exterior vapor barrier that keeps outside humidity from penetrating into walls. The first design concept is the barrier system where all moisture is resisted by the exterior surface material also often.

Whether or not you need a vapor retarder hinges on three main factors. 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. Dupont tyvek drainwrap is a moisture barrier designed to provide enhanced drainage in areas subject to extreme wind driven rain. The cool surface is the sheathing assuming no exterior insulation.