Unvented Attic Cold Climate

Air impermeable insulation typically spray foam installed to the underside of the roof sheathing.

Unvented attic cold climate.

Vented roofs serve a number of different purposes and their roles vary from climate to climate. Unvented attics have higher temperatures on 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. Two acceptable methods for insulating an unvented attic assembly in all climates are as follows.

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. See the irc or the guide unvented attic insulation for details. In colder climates the main purpose of a vented roof is to keep the roof cold and reduce the formation of ice dams.

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. 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. 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.