Foam Insulation No Roof Vent

The principle behind soffits is to allow air to circulate in and around the attic.

Foam insulation no roof vent.

Heat from the house rises up to the attic but when there isn t one the heat rises up to the roof. Foam insulation can play an important role in both vented and un vented roof assemblies. 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. It has been said that insulating with spray foam insulation at the roof line will lead to moisture problems with the roof sheathing.

But spray foam insulation used at the underside of the roof deck would need to be covered by a thermal barrier and intumescent coatings are commonly used. Rigid foam and spray foam are two of them. Better to have a vent channel and no vent openings than vice versa as the air gap allows some evaporative drying and hygric redistribution. You don t need soffit or gable vents either since the attic is now conditioned space.

One of the most common reasons to put spray foam on the roofline is to avoid having to air seal the attic floor because the attic is connected with the air in the house and indoor air is more humid than outdoor air which can cause moisture problems. However second only to an unvented closed cell foamed roof with bituthene membrane a vented roof with fibrous insulation and no vent channel from soffit to ridge is a recipe for disaster. All insulation materials require proper venting. In most residential homes the soffit and associated vents is the structural part of the roof that hangs over the side of the home.

Cathedral roofs especially need a lot more insulation between the ceiling and the rafters because there usually isn t any attic space. The movement of air into indirect conditioning of an unvented attic is a slow gradual process that will not be noticeable by occupants and typically will not put any strain on the hvac system. In an un vented roof foam can serve as the air barrier and vapor retarder and prevent moisture from getting in to the roof.