Open Cell Spray Foam Air Barrier

Open cell foam makes a good air barrier but it s vapor permeable.

Open cell spray foam air barrier.

Open cell foam is full of cells that aren t completely encapsulated. If you put spray foam insulation in a building it needs a thermal barrier. 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. This makes the foam a softer more flexable material.

This premiere insulation has many benefits including help with moisture and sound control and the ability to help lower heating and cooling bills. 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. If there s a fire in the building a thermal barrier keeps the combustible spray foam from the flames to increase fire resistance. 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 spray foam is not a moisture vapor barrier and will allow moisture to pass. If there s a roof leak water will pass through the foam and you will quickly be able to find your problem. To produce open cell requires the use of an a component iso and a blended b component resin which contains zero ozone depleting blowing agents catalysts polyols and fire retarding materials. In other words the cells are deliberatly left open.

That means water vapor can migrate through the foam even when the bulk movement of air is blocked. 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. Open cell is a two component light density one to one by volume spray polyurethane foam. So if you re considering spraying foam to the roof deck of your new or existing home you want open cell.

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. No ignition barrier coating is required when used in assembly specific attic applications. 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.

That s what separates it from the occupied spaces. It is fairly vapor permeable. However it is not a vapor barrier.