Spray Foam Roof Or Vent

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 foam roof or vent.

Unlike solid insulation products that require careful measurement cutting and fitting spray foam can cover even the most uneven surface instantly. 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. This is not an issue specific to spray foam as much as it is a characteristic of peel and stick membranes. All insulation materials require proper venting.

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. Nothing unusual about that. For best performance the airspace in the vent chute should be a minimum of 2 in. Heat from the house rises up to the attic but when there isn t one the heat rises up to the roof.

Unvented attic assemblies unvented attics rely on an air impermeable insulation installed to the roof deck s underside i e. Rigid foam and spray foam are two of them. Unless you re bulk filling rafter bays between 2 10 or 2 8 rafters with closed cell spray foam this approach will likely require you to fur out the rafters to accommodate additional insulation to achieve desired r values. The photo above shows the scar from a power attic ventilator installed in a spray foam attic but i ve heard of several cases where roofers installed or tried to ridge vents.

This alternative to traditional building insulation fiberglass can be applied into wall cavities holes concrete slabs and even onto roof tiles and. Sealed attics should not have any type of attic ventilation connecting it to the outside. In an un vented roof foam can serve as the air barrier and vapor retarder and prevent moisture from getting in to the roof. Cathedral roofs especially need a lot more insulation between the ceiling and the rafters because there usually isn t any attic space.

If spray foam is used a vent space may still be needed directly under the roof deck. Wood has an r value of about one per inch of thickness. Foam insulation can play an important role in both vented and un vented roof assemblies.