Attic Closed Cell Foam Underlayment

Control rain in any roof assembly an underlayment e g.

Attic closed cell foam underlayment.

Closed cell foam has a higher r value than open cell foam usually about 6 0 per inch. In general most closed cell foam and many open cell foam products can be installed without the need of an intumescent coating in an unvented attic and therefore can go bare provided a drywall ceiling 15 minute thermal barrier directly below the attic exists. A foams r value is its resistance to heat flow or in other words how well they insulate. A sealed and insulated roof deck can t dry inward to the attic if the roofing happens to let water.

Many builders in cold climates use closed cell spray foam instead because of its lower water vapor permeability which means it doesn t need the extra step of installing a vapor retarder. Closed cell medium density spray polyurethane foam ccspf insulation can be used to create an unvented roof assembly for any climate zone. It also stops air flow through and. But foam also traps moisture in the roof in case of a leak.

Closed cell foam can also increase the racking strength of attic walls which is the ability of a structure such as a wall to withstand horizontal forces. 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. But open cell spray foam with a vapor retarder can work too. Unvented roofs with spray foam applied to the underside of the roof deck have been used since the mid 1990s.

The underlayment is a vapor barrier called rooftop guard. This is a liftime metal roof. Closed cell spray foam works in all climates but especially well in climate zones 5 through 8 where high r values are desired and where air impermeable insulation also must be a vapor retarder. Closed cell foam can be over three times that with a density of 1 75 pounds per cubic foot or more.

Low density open cell foam is permissible but in climate zones 5 and above it has to be covered with a vapor retarder coating like rigid foam or.