Unvented Attic Cold Climate

Vented roofs serve a number of different purposes and their roles vary from climate to climate.

Unvented attic cold climate.

Unvented attics have higher temperatures on the underside of the roof sheathing. See the irc or the guide unvented attic insulation for details. 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. A secondary goal is to vent moisture that infiltrates the attic from the conditioned home.

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

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. 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.