Unvented Attic Cold Climate

Two acceptable methods for insulating an unvented attic assembly in all climates are as follows.

Unvented attic cold climate.

Unvented attics have higher temperatures on the underside of the roof sheathing. Air impermeable insulation typically spray foam installed to the underside of the roof sheathing. A secondary goal is to vent moisture that infiltrates the attic from the conditioned home. 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.

In colder climates the main purpose of a vented roof is to keep the roof cold and reduce the formation of ice dams. 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. 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. This is done by using what is referred to as air impermeable insulation such as rigid foam board or spray foam.

For example if an r 80 unvented cathedralized attic is to be constructed in a cold climate a minimum of r 40 50 should be air impermeable insulation installed and layered according to section r806 5 of the 2012 irc figure 4. Vented roofs serve a number of different purposes and their roles vary from climate to climate. In cold climate locations with significant snowfalls ice dam formation on roofs is a real concern.