Foam Insulation Roof Ventilation

Nothing unusual about that.

Foam insulation roof ventilation.

Rigid foam and spray foam are two of them. A lot of builders and homeowners are going with spray foam insulation because of the airtightness benefits but then the questioner mentioned that the spray foam contractor had intentionally left big holes to the outside by not sealing the gable vents. Heat from the house rises up to the attic but when there isn t one the heat rises up to the roof. Sometimes humidity levels spike in an attic after a spray foam job.

Unvented attic assemblies unvented attics rely on an air impermeable insulation installed to the roof deck s underside i e. Earlier this year i got a question about a home that had spray foam insulation in the attic. Zones 5 6 7 and 8 in that the manufacturers of these materials assume that roof deck may require ventilation to assist drying. Spray polyurethane foam is a chemical product that is created by two materials isocyanate and polyol resin that will react with each other when they are mixed and will expand up to 30 to 60 times its liquid volume as it is sprayed in place.

Attic ceiling to stop airborne moisture from reaching a cold surface and condensing inside the building envelope in this design insulation effectively separates the interior and exterior spaces while slowing down moisture flow so the dewpoint is not achieved within. Cathedral roofs especially need a lot more insulation between the ceiling and the rafters because there usually isn t any attic space. In an un vented roof foam can serve as the air barrier and vapor retarder and prevent moisture from getting in 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. Staple plastic or foam baffles to the roof sheathing near the eaves to keep the material away. High attic humidity often results from spray foam insulation. The airflow from the soffits to the ridge vent keeps the roof cool and prevents ice dams and the material will block that flow.

Care should be taken with these assemblies particularly in cold climate zone locations i e. If a blower door test reveals that your spray foam insulation reduced ventilation beyond an acceptable level you may need to install one of these units in your home. For the same reason insulation shouldn t touch the roof s underside.