Open Cell Foam Roof Deck

Open cell spray foam is not a moisture vapor barrier and will allow moisture to pass.

Open cell foam roof deck.

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. It would come with 3 1 2 or 4 of polyiso adhered to a 7 16 deck. Open cell foam is just that open cell. If there s a roof leak water will pass through the foam and you will quickly be able to find your problem.

Open cell spray foam can also be used to create an unvented attic in cold climate zones provided code requirements for a vapor retarder are followed. Unvented roofs with spray foam applied to the underside of the roof deck have been used since the mid 1990s. To do 8 safely it has to be done in two lifts with a cooling curing period between lifts. Common sense tell s me if this is valid marketing then what stops water vapor from moving through the foam under pressure.

Like thicker layers of hfc blown closed cell foam at r30 most open cell foam is a fire hazard during the curing period right after installation. 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. 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.