Open Cell Foam Roof Deck

Common sense tell s me if this is valid marketing then what stops water vapor from moving through the foam under pressure.

Open cell foam roof deck.

Instead of installing a couple layers of polyiso with staggered joints and then decking he is proposing using a product like the gaf thermacal insulated nailing base. So if you re considering spraying foam to the roof deck of your new or existing home you want open cell. If there s a roof leak water will pass through the foam and you will quickly be able to find your problem. It would come with 3 1 2 or 4 of polyiso adhered to a 7 16 deck.

Unvented roofs with spray foam applied to the underside of the roof deck have been used since the mid 1990s. Chemical manufacturer s claim if a roof leaks water will migrate through the foam structure therefore not trapping the water. Some spray foam manufactures have tested primer coating products that result in the formulation of a class ii vapor retarder directly on the surface of the open cell spray foam. Open cell spray polyurethane foam or closed cell spray polyurethane foam ccspf insulation can be sprayed along the underside of the roof sheathing to provide a conditioned and insulated attic space that can be durable and efficient in all climate zones see figure 1.

To do 8 safely it has to be done in two lifts with a cooling curing period between lifts. Open cell spray foam is not a moisture vapor barrier and will allow moisture to pass. Open cell foam is just that open cell. Even though it s air tight open cell foam is still pretty vapor open at r30.