Foam Insulation No Roof Vent

Cathedral roofs especially need a lot more insulation between the ceiling and the rafters because there usually isn t any attic space.

Foam insulation no roof vent.

There is no need for a ridge vent in this application since the ccspf seals the roof. 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. Rigid foam and spray foam are two of them. 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.

In an un vented roof foam can serve as the air barrier and vapor retarder and prevent moisture from getting in to the roof. You don t need soffit or gable vents either since the attic is now conditioned 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. The principle behind soffits is to allow air to circulate in and around the attic.

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. Better to have a vent channel and no vent openings than vice versa as the air gap allows some evaporative drying and hygric redistribution. It has been said that insulating with spray foam insulation at the roof line will lead to moisture problems with the roof sheathing.

Foam insulation can play an important role in both vented and un vented roof assemblies. 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. To add to what brian said closed cell spray foam ccspf applied directly to the underside of the roof sheathing would seal a ridge vent shut.