Attic Venting With Spray Foam

Heat from the house rises up to the attic but when there isn t one the heat rises up to the roof.

Attic venting with spray foam.

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 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. Cathedral roofs especially need a lot more insulation between the ceiling and the rafters because there usually isn t any attic space. Unvented attic assemblies unvented attics rely on an air impermeable insulation installed to the roof deck s underside i e.

This construction approach was first used in the 1970s and it has been implemented much more widely since it was first included in the international code council s icc model building code in 2007 irc section 806 4. Unvented attics sometimes called sealed enclosed or encapsulated attics feature insulation on the underside of the roof decking rather than on the attic floor. This alternative to traditional building insulation fiberglass can be applied into wall cavities holes concrete slabs and even onto roof tiles and. Nothing unusual about that.

In cold climates the primary purpose of attic or roof ventilation is to maintain a cold roof temperature to control ice dams created by melting snow and to vent moisture that moves from the conditioned space to the attic ventilation acts to bypass the vapour barrier created by most roof membranes. Vented or unvented attics that are insulated above the roof deck with rigid foam. Unvented attics that are insulated on the underside of the roof deck with blown spray foam. 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.

Earlier this year i got a question about a home that had spray foam insulation in the attic. Tell them the attic is to have no ventilation of any type. Most unvented attics incorporate spray polyurethane foam spf on the underside of the roof deck and attic walls. 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.

Typically spray foam photograph 2. Sealed attics should not have any type of attic ventilation connecting it to the outside. Rigid foam and spray foam are two of them.