Unvented Attic Cold Climate

In cold climate locations with significant snowfalls ice dam formation on roofs is a real concern.

Unvented attic cold climate.

Unvented attics have higher temperatures on the underside of the roof sheathing. 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. Two acceptable methods for insulating an unvented attic assembly in all climates are as follows. In colder climates the main purpose of a vented roof is to keep the roof cold and reduce the formation of ice dams.

Air impermeable insulation typically spray foam installed to the underside of the roof sheathing. People usually vent attics in cold climates to prevent moisture accumulation in the roof sheathing and control ice dams. See the irc or the guide unvented attic insulation for details. A secondary goal is to vent moisture that infiltrates the attic from the conditioned home.

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. In cold climates moisture in roof assemblies typically comes from inside and the key to problems with moisture is the temperature of the roof sheathing. In any event a growing number of manufacturers are offering competitive warranties for roofing over unvented attic assemblies recognizing a significant marketing opportunity for their products.