Open Cell Foam Roof Deck

Chemical manufacturer s claim if a roof leaks water will migrate through the foam structure therefore not trapping the water.

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. 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. 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. 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 is not a moisture vapor barrier and will allow moisture to pass. 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. 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. Even though it s air tight open cell foam is still pretty vapor open at r30.

To do 8 safely it has to be done in two lifts with a cooling curing period between lifts. 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. Open cell foam is just that open cell.