Attic Closed Cell Foam Underlayment

A sealed and insulated roof deck can t dry inward to the attic if the roofing happens to let water.

Attic closed cell foam underlayment.

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. 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. Closed cell medium density spray polyurethane foam ccspf insulation can be used to create an unvented roof assembly for any climate zone. But foam also traps moisture in the roof in case of a leak.

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. 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. Closed cell foam can be over three times that with a density of 1 75 pounds per cubic foot or more. The underlayment is a vapor barrier called rooftop guard.

Applying closed cell spray insulation to the underside of a roof deck at the sheathing to truss connection can double or triple the strength of the assembly boosting the roof sheathing s resistance to wind uplift in a hurricane. But some closed cell foams like tiger foam s e84 closed. It also stops air flow through and. Unvented roofs with spray foam applied to the underside of the roof deck have been used since the mid 1990s.

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. Control rain in any roof assembly an underlayment e g. Closed cell foam has a higher r value than open cell foam usually about 6 0 per inch. A foams r value is its resistance to heat flow or in other words how well they insulate.

This is a liftime metal roof.