Spray Foam Underside Of Roof In Attic

When spray foam is installed on the underside of the roof deck the attic space is insulated from heat that otherwise would be entering the attic.

Spray foam underside of roof in attic.

An attic that is properly vented has 50 intake of fresh air and 50 exhaust of the hot air. For almost 10 years now we have been recommending that if a client spray foams the underside of the roof deck we prefer closed cell then they should drop both a supply and return vent into that attic cavity it essentially becomes another room in the house though of course we are not as concerned about proper sizing of the vents as we are that we are helping to fight humidity in the attic. The roofing materials are installed and consist of timberline shingles and full coverage ice and water barrier the entire roof. Attic ceiling to stop airborne moisture from reaching a cold surface and condensing inside the building envelope.

Unvented roofs with spray foam applied to the underside of the roof deck have been used since the mid 1990s. You should never do this. 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. It s not coming from above the roof and it s not some new moisture source resulting from the spray foam.

In this design insulation effectively separates the interior and exterior spaces while slowing down moisture flow so the dewpoint is not achieved within the building envelope. Most unvented attics incorporate spray polyurethane foam spf on the underside of the roof deck and attic walls. The insulation reduces wildly high temperature spikes and so the attic becomes a conditioned part of the home like any other room. The installer sprayed foam directly on the metal flues.

Unvented attics rely on an air impermeable insulation installed to the roof deck s underside i e. Lstiburek takes blame for bad language. The main concern with spray foam insulation and shingle warranty is proper attic ventilation. You ll also see another safety hazard and code violation.

Most people do not realize the requirements for proper venting of an attic. 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. The attic will be a conditioned space and i m planning to apply spray foam insulation to the underside of the roof sheathing. If you do not have proper ventilation you are in essence cooking your shingles.

If you look closely you ll see two exhaust flues on the left side. Moisture generated indoors or that infiltrates into the home is responsible for the bulk of the moisture in an attic insulated with spray foam on the underside of the roof sheathing.