Attic Closed Cell Foam Underlayment

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.

Attic closed cell foam underlayment.

This is a liftime metal roof. The underlayment is a vapor barrier called rooftop guard. It also stops air flow through and. 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.

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. A sealed and insulated roof deck can t dry inward to the attic if the roofing happens to let water. Minimum of felt paper should be installed as the primary water barrier under the roofing. Closed cell medium density spray polyurethane foam ccspf insulation can be used to create an unvented roof assembly for any climate zone.

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. 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. But foam also traps moisture in the roof in case of a leak. A foams r value is its resistance to heat flow or in other words how well they insulate.

Closed cell foam has a higher r value than open cell foam usually about 6 0 per inch. But some closed cell foams like tiger foam s e84 closed. Closed cell foam can be over three times that with a density of 1 75 pounds per cubic foot or more. 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.

But open cell spray foam with a vapor retarder can work too.