Unvented Attic Cold Climate

Unvented attics have higher temperatures on the underside of the roof sheathing.

Unvented attic cold climate.

People usually vent attics in cold climates to prevent moisture accumulation in the roof sheathing and control ice dams. 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. 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. Vented roofs serve a number of different purposes and their roles vary from climate to climate. 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. Two acceptable methods for insulating an unvented attic assembly in all climates are as follows.

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. 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. See the irc or the guide unvented attic insulation for details.