Spray Foam Underside Of Roof In Attic

Most unvented attics incorporate spray polyurethane foam spf on the underside of the roof deck and attic walls.

Spray foam underside of roof in attic.

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. The attic you see in the photo here is a different home but it does have one feature in common besides the spray foam. Lstiburek takes blame for bad language.

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. Unvented roofs with spray foam applied to the underside of the roof deck have been used since the mid 1990s. If you do not have proper ventilation you are in essence cooking your shingles.

Unvented attics rely on an air impermeable insulation installed to the roof deck s underside i e. 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. 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. An attic that is properly vented has 50 intake of fresh air and 50 exhaust of the hot air.

Open cell spray polyurethane foam or closed cell spray polyurethane foam ccspf insulation can be sprayed along the underside of the roof sheathing to provide a conditioned and insulated attic space that can be durable and efficient in all climate zones see figure 1. Unlike solid insulation products that require careful measurement cutting and fitting spray foam can cover even the most uneven surface instantly. The roofing materials are installed and consist of timberline shingles and full coverage ice and water barrier the entire roof. It s not coming from above the roof and it s not some new moisture source resulting from the spray foam.

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 main concern with spray foam insulation and shingle warranty is proper attic ventilation. 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. You should never do this.

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. You ll also see another safety hazard and code violation.