Spray Insulation Roof Ventilation

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.

Spray insulation roof ventilation.

All insulation materials require proper venting. Heat from the house rises up to the attic but when there isn t one the heat rises up to the roof. Spray foam insulation will not prevent ventilation and so there s no need to avoid it thinking that it will result in mould and mildew from building up inside the attic space. Moving the air control layer and thermal control layer to the underside of the roof deck has significant advantages in cases where the hvac system is located in the attic.

This illustration shows a sloped roof with cavity spray foam insulation sprayed on the underside of the roof deck and covered with sprayed on thermal or ignition barrier coating. 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. For the same reason insulation shouldn t touch the roof s underside.

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. Nothing unusual about that. Polyurethane or polystyrene spray foams can provide thorough coverage to roof rafters and attic walls in much less time than is needed for other materials.

Care should be taken with these assemblies particularly in cold climate zone locations i e. Unvented attic assemblies unvented attics rely on an air impermeable insulation installed to the roof deck s underside i e. Unlike solid insulation products that require careful measurement cutting and fitting spray foam can cover even the most uneven surface instantly. Rigid foam and spray foam are two of them.

The most important thing to remember is to use the correct type of insulation and to ensure it is installed correctly. Earlier this year i got a question about a home that had spray foam insulation in the attic. The airflow from the soffits to the ridge vent keeps the roof cool and prevents ice dams and the material will block that flow.