Open Cell Spray Foam In Attic

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 spray foam in attic.

The role of open cell spray foam. Creates a strong airtight seal. It s the wood decking that stores the moisture though. Open cell spray foam insulation doesn t store the moisture.

It s just a pathway. 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. Moisture is also another huge issue when it comes to spray foam insulation in an 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.

Builders should consider these costs before specifying open cell spray foam. Open cell foam weighs 1 2 pound per cubic foot and closed cell weighs 2 lbs per cubic foot. This makes the foam a softer more flexable material. 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.

In other words the cells are deliberatly left open. Spray polyurethane foam is a strong expansive product that quickly works to seal various cracks and holes in your crawl space attic and walls. 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 is full of cells that aren t completely encapsulated.

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. 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. 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.

It has been said that insulating with spray foam insulation at the roof line will lead to moisture problems with the roof sheathing.