Open Cell Spray Foam Air Barrier

Open cell spray foam is an excellent air barrier.

Open cell spray foam air barrier.

Created using a similar process as closed cell foam open cell foam is designated to be vapor semi permeable as the formation of the cells in the material are broken rather than closed. Open cell foam is full of cells that aren t completely encapsulated. Open cell spray foam is not a moisture vapor barrier and will allow moisture to pass. Open cell foam makes a good air barrier but it s vapor permeable.

Spray foam insulation as an air barrier system the air barrier association of america abaa defines an air barrier system as a system of building assemblies within the building enclosure designed installed and integrated in such a manner as to stop the uncontrolled flow of air into and out of the building enclosure. No ignition barrier coating is required when used in assembly specific attic applications. Open cell is a two component light density one to one by volume spray polyurethane foam. This becomes an important consideration when the foam is sprayed between rafters on the underside of the roof sheathing to create a conditioned attic in a cold climate.

A spray insulation is referred to open cell or closed cell because of the difference between the small bubbles cells that make up the foam. This premiere insulation has many benefits including help with moisture and sound control and the ability to help lower heating and cooling bills. One step insulation air barrier for homes commercial buildings icynene open cell and closed cell spray foam insulates and air seals in one step. However it is not a vapor barrier.

Similar to the holes inside a sponge air can permeate the open cells more easily making open cell foam more porous and absorbent than closed cell foam. Its use also means expensive air membranes on the exterior of the wall sheathing can be avoided or scaled back in scope thereby reducing construction costs. When installed in a cold climate between the rafters of a ceiling to cathedralize an attic open cell spray foam needs to be protected with a vapor retarder to prevent water vapor from diffusing through the foam and contacting the cold roof sheathing. So if you re considering spraying foam to the roof deck of your new or existing home you want open cell.

In other words the cells are deliberatly left open. If there s a roof leak water will pass through the foam and you will quickly be able to find your problem. This makes the foam a softer more flexable material. If there s a fire in the building a thermal barrier keeps the combustible spray foam from the flames to increase fire resistance.

That means water vapor can migrate through the foam even when the bulk movement of air is blocked. It is fairly vapor permeable. Therefore using open cell spray foam within a wall cavity with either metal or wood studs can constitute the main component of an air barrier system.