Open Cell Spray Foam In Attic

In climate zones 1 2 3 and 4 the use of open cell spray foam with their vapor permeable nature will allow the drying of roof sheathing and framing as diffusion allows moisture to pass through the spray foam out of sheathing and structural elements.

Open cell spray foam in attic.

It has a relatively high vapor permeance 3 perms at a thickness of 6 allowing water vapor to migrate to the roof decking at night and back into the attic air in the daytime. This airtight seal helps to decrease homeowner costs including utility costs. 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. Whereas too little spray foam insulation can leave for thermal bypass because of the complete lack of insulation in the attic.

While open cell spray foam seems relatively inexpensive its use on the underside of roof sheathing may require a protective layer of 1 2 inch drywall an interior vapor retarder and special hvac runs to condition the air in the attic. Creates a strong airtight seal. Moisture is also another huge issue when it comes to spray foam insulation in an attic. Builders should consider these costs before specifying open cell spray foam.

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. There is 300 difference there but the cost they give you is about a third difference and open cell foam at 12 inches will not give you the performance of 2 inches of closed. Open cell foam has an r value of about 3 5 to 3 7 per inch while closed cell foam has an r value of about 6 per inch. The role of open cell spray foam.

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 foam weighs 1 2 pound per cubic foot and closed cell weighs 2 lbs per cubic foot. Closed cell foam can also increase the racking strength of attic walls which. Open cell spray foam insulation doesn t store the moisture.

Open cell foam is full of cells that aren t completely encapsulated. It s just a pathway. Spray polyurethane foam is a strong expansive product that quickly works to seal various cracks and holes in your crawl space attic and walls. It s the wood decking that stores the moisture though.

This makes the foam a softer more flexable material.