Unvented Roof Spray Foam

The plan is to spray open cell foam under the roof deck.

Unvented roof spray foam.

Unvented roof strategies with spray polyurethane foam spf have been used since the mid 1990s to provide durable and efficient building enclosures. Minimum of felt paper should be installed as the primary water barrier under the roofing. This is the recommendation of all three local insulation installers. If you don t want to use sips or nailbase there are four basic approaches.

Unvented roof assemblies should be insulated either with air impermeable insulation rigid foam or spray polyurethane foam or with a combination of foam and air permeable insulation. Four options for building an unvented roof assembly. For unvented attics having the spray foam layer applied continuously from the roof wall intersection to the roof peak at the specified thickness encapsulating the entire interior surface area of the attic will hinder airborne moisture entry while providing an energy efficient environment. Foam insulation can play an important role in both vented and un vented roof assemblies.

Lstiburek takes blame for bad language. 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. Most unvented attics incorporate spray polyurethane foam spf on the underside of the roof deck and attic walls. Closed cell medium density spray polyurethane foam ccspf insulation can be used to create an unvented roof assembly for any climate zone.

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. As we note in our blog post yes unvented roof assemblies can be insulated with fiberglass a wufi post the building code written for the foam industry does ask for air impermeable insulation or foam. However as the future owner i m beginning maybe a bit too late to read about unvented roofs and i m wondering if this is really the best option. It s not coming from above the roof and it s not some new moisture source resulting from the spray foam.

However the intent of the code can be readily met with an assembly that includes fibrous insulation and an inboard air barrier and vapor control layer and is regularly approved for use as such. Open cell spray polyurethane foam ocspf and closed cell spray polyurethane foam ccspf insulation sprayed to the underside of roof sheathing is a popular strategy for increasing roof insulation levels in all climate zones.