Unvented Roof Foam Insulation

Murmurs and hearsay about open cell spray foam insulation have been gaining traction for a while.

Unvented roof foam insulation. We agree that avoiding sheathing rot is critical and that air permeable insulation such as fiberglass or cellulose cannot be used alone. This construction approach was first used in the 1970s and it has been implemented much more widely since it was first included in the international code council s icc model building code in 2007 irc section 806 4. Not long ago someone even told me that in florida roofing companies won t let their workers go up on roofs with open cell spray foam because the roofs are so spongy the guys fall right through. In an un vented roof foam can serve as the air barrier and vapor retarder and prevent moisture from getting in to the roof cavities.

Spray foam insulation in an unvented attic assembly has been one of the most researched and widely implemented innovations of recent years. Insulating and providing airtightness with spray foam at the underside of the roof as part of an unvented attic assembly will elevate such concerns. Two potential unvented roof assemblies. Four options for building an unvented roof assembly.

A properly functioning un vented roof. Foam and the roof assembly foam insulation can play an important role in both vented and un vented roof assemblies. If you don t want to use sips or nailbase there are four basic approaches. Closed cell medium density spray polyurethane foam ccspf insulation can be used to create an unvented roof assembly for any climate zone.

Most unvented attics incorporate spray polyurethane foam spf on the underside of the roof deck and attic walls. 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 soffits etc which make it difficult to achieve an airtight ceiling plane. Monolithic continuous exterior insulation ci above structural sheathing. But in it unfortunately all four options provided are dominated by foam.

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. In the most recent issue of fine homebuilding martin holladay wrote a piece on insulating unvented roof assemblies. Owens corning a leading manufacturer of fiberglass insulation is now promoting a package of products basically blown in fiberglass insulation and a new type of insulation netting to create unvented conditioned attics. It rots roofs people have told me.

Owens corning calls this proprietary insulation method the propink high performance conditioned attic system.