Vented attics typically are designed to remove excess heat, reduce the potential for ice damming, and remove moisture from within the building envelope. Insulating your attic with spray foam can change this dynamic in your attic. Because the spray foam is applied to the bottom of the roof deck, rather than the floor of the attic, the interior of the attic becomes less like outside air and more like the air in the rest of the house.

Spray foam insulation can also be applied to the floor of the attic and achieve similar results.

If sufficient insulation is applied, this roof deck insulation in turn reduces ice damming because the roof surface is now colder in the winter, thus avoiding premature melting caused by the heat within your attic. Conversely, less heat passes through the roof of the house in the summer, thus keeping the house cooler, avoiding heat buildup, and reducing cooling expense.

Adequate insulation also reduces the incidence of condensation in the winter on the base of the roof deck because the insulation keeps the interior side of the foam warmer. In the summer this reverses, resulting in little chance of condensation on the exterior of the building.

Heat loss is also minimized for any ductwork running through the attic, since the air this area is now semi conditioned.

Unvented attics save energy, especially in buildings with ductwork in the attic, and have proven energy savings of 9-23% in hot climates.