Unvented Attic Open Cell Foam

Thanks for sharing the language of your proposed code change proposal concerning unvented attics insulated with open cell spray foam.

Unvented attic open cell foam. Yep and you re not alone. It appears that many opinions presented are based on limited building science field research generalize a complicated building science situation and doesn t fully explain the continued successful long term performance of. Foam insulation can play an important role in both vented and un vented roof assemblies. Install insulation along the underside of the roof deck of an unvented attic rather than on the ceiling deck of a vented attic for either of two reasons.

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. To provide an unvented conditioned space for locating hvac equipment in the attic and or to provide a continuous thermal barrier for designs that have complex coffered ceiling planes and or numerous penetrations for lights speakers vents. Open and closed cell foam insulation use a blowing agent to forms the cells within it. Closed cell foams use enovate also known as 245fa.

Don t install closed cell foam. Thanks for spelling out the smoke detector in the duct solution. An alternate to spray foam insulation in an unvented attic is plenum trusses which allow you create a reverse bulkhead above the ceiling plane that is insulated. Open cell foams use water as a blowing agent.

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. The proposal you shared doesn t address the fire safety concerns that have been raised relating to the installation of forced air registers or return air grilles in attics with spray foam that lacks a layer of 1. In a vented roof foam can seal the openings and serve as an air barrier and a vapor retarder in addition to its insulating function. Dupont roofliner is a vapor barrier and therefore cannot be used on an unvented roof.

The myth that open cell is more economical is bullshit. Another study s computer model indicated that open cell foam insulation is riskier than closed cell foam in all us climate zones. There is 300 difference there but the cost they give you is about a third difference and open cell foam at 12 inches will not give you the performance of 2 inches of closed. Yeah since so many spray foam attics without direct conditioning have been fine it s probably overkill to suggest doing it for all of them but i don t think the extra energy use will be much.

In an un vented roof foam can serve as the air barrier and vapor retarder and prevent moisture from getting in to the roof. Lately discussions related to open cell spray foam in unvented attics vapor drives and humidity levels have appeared.