Wall Vapor Barrier Foam

Xps foam extruded polystyrene before building the interior walls to create a thermal break vapor barrier.

Wall vapor barrier foam.

Frankly the vapor barrier on the wall prior to foam won t buy you much unless you re going to use a layer of foam less than 1 1 2. A vapor barrier reduces the movement of water vapor by. If you properly install a layer of at least 1 1 2 of closed cell foam tape all the seems seal the edges with foam spray foam in a can then you ve created a thermal and vapor barrier. On the exterior concrete walls i glued 2 in.

However an installation between the studs can pose a challenge. Vapor barriers are sheets of plastic or other material placed on one side of insulation sheets. 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. Not every wall does.

On the interior walls between the finished and unfinished areas i was going to use rockwool insulation with 1 2 sheetrock on both sides. 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. 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. A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter.

In any case the vapor barrier must point to the warm side. Whether or not you need a vapor retarder hinges on three main factors. 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. To complete the vapor barrier you would want to foam seal or tape all the sides where the rigid meets timber because these gaps will facilitate vapor flow.

In all cases a functional air barrier system was provided in the form of sealed drywall or a continuous chain of spf and wood as this is required. Rigid foam insulation is usually a qualified vapor barrier. Water vapor can pass through building materials in several ways including direct transmission and by heat transfer but studies suggest that fully 98 percent of the moisture transfer through walls occurs through air gaps including cracks around electrical fixtures and outlets and gaps along baseboards. 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.

My plan is to leave a 1 gap between the rigid foam and my stud wall then insulate my stud wall cavity with unfaced batts no vapor barrier. The research reported here investigated the ability of typical framed walls using spray polyurethane foam insulation with and without additional vapor barrier layers to meet these requirements. However an installation between the studs can pose a challenge. After the insulation is in place you will want to add a vapor retarder sometimes called a vapor barrier if you need one.

I haven t decided on a floor method yet but i d like to have some type of subfloor so my flooring isn t directly sitting on the cold concrete.