Unvented Roof Spray Foam

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.

Unvented roof spray foam.

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. This is the recommendation of all three local insulation installers. Closed cell medium density spray polyurethane foam ccspf insulation can be used to create an unvented roof assembly for any climate zone. 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.

Control rain in any roof assembly an underlayment e g. 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. Moisture generated indoors or that infiltrates into the home is responsible for the bulk of the moisture in an attic insulated with spray foam on the underside of the roof sheathing. Four options for building an unvented roof assembly.

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. 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. Unvented roof strategies with spray polyurethane foam spf have been used since the mid 1990s to provide durable and efficient building enclosures.

Lstiburek takes blame for bad language. Most unvented attics incorporate spray polyurethane foam spf on the underside of the roof deck and attic walls. If you don t want to use sips or nailbase there are four basic approaches. Minimum of felt paper should be installed as the primary water barrier under the roofing.

Foam insulation can play an important role in both vented and un vented roof assemblies. 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.