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Community and Q&A

Open-cell spray foam warning!

jkmurphy1 | Posted in Energy Efficiency and Durability on

We live in the Pittsburgh PA area, which I believe is in climate Zone 5. This is more of a warning to anyone considering open cell spray foam, or anyone that may currently have it. We had the foam sprayed in our attic back in 2007 to including attic walls, gables, and roof decking which gave us the “closed envelope”/ un-vented attic (approx 1800 sq ft of living space). The thickness of the foam was from 6 ” to 10″ depending on the area. The gable walls were sprayed to the thickness of 3 1/2 “. Our attic is a walk-in, soon to be a future living space. December 2011 we noticed a small water spot on the floor of our attic. After removing the foam in this area, we noticed a very large air gap in which the foam was not adhered to the decking. Mold and wetness was present. The water spot was from condensation that had built up in this area.

We contacted the installer of the foam at this point. The company came back and starting randomly removing small areas of foam throughout the attic. There were several areas in which the foam was pulled away from the roof decking, and all roofing nails were rusted. Even where the foam did adhere, the nails were rusted. Many of these areas had extensive mold. There were many areas that had voids and tunneling that you would not have found until you began removing the foam off the decking. Looking at it from the living space, the foam appeared to be adhered to the substrate. All areas had condensation issues, but it seemed most of the mold was on the north side of the house. This is called north face frosting, where the sheathing does not get enough radiant heat on the shingles and frost during the winter. This creates moisture then mold. as one mold expert had mentioned which examined the attic.

Prior to removing the foam, a forensic engineer determined the mold growth on the underside of the roof decking was the result of condensation and voids between the foam insulation and the roof decking. Water vapor entered the voids between the decking and foam insulation via outside air passing through openings between the foam and the soffit vent baffles and interior air via small openings between the insulation and the roof framing. Interior moisture readings were done, and were within normal ranges. So, our house was not the cause of this problem.

All the foam was removed in July 2012. We paid out of pocket $2000 in mold remediation which the installer or the foam company took responsibility for. Having two kids with asthma and allergies, we had no choice but to get the mold removed immediately.

If you are considering open cell spray foam, you better reconsider your options. If you currently have open cell foam, you better dig deeper than just looking at it. If we had not noticed this small area of condensation, about the size of a baseball, we would have had no reason to think there was a problem. Our attic area would of been slowly but surely rotting away from mold and condensation, which was surely caused by the open cell spray foam.

Right now we have no insulation in our attic. We are considering our options. If you experienced any problems with your spray foam, or have any comments, we would appreciated it.

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  1. GBA Editor
    Martin Holladay | | #1

    J. Murphy,
    The Building Science Corporation has been warning for many years that open-cell spray foam should not be used in Climate Zones 5 or colder to create an unvented conditioned attic, because of the risk of precisely the problems you describe. The open-cell foam, being vapor-permeable, allows water vapor to diffuse through the foam. The moisture accumulates on the cold roof sheathing during the winter, leading to possible mold or rot.

    Until recently, the BSC recommended that insulation contractors should spray the cured foam with vapor-retarder paint to avoid this problem. However, further testing has convinced them that, because of the open-pore surface of the cured foam, vapor-retarder paint does NOT work on cured foam.

    Their current recommendation: either used closed-cell foam for this application, or be sure to install gypsum drywall over all of the open-cell foam. Once the drywall is installed, the drywall must be painted with vapor-retarder paint.

    The GBA Encyclopedia article on spray polyurethane foam includes a warning about the problem you are experiencing, and advises that attics in climate zones 5 and colder be insulated with closed-cell spray foam UNLESS the installation includes gypsum wallboard painted with vapor-retarder paint.

  2. davidmeiland | | #2

    This installation sounds like it had quite a few voids, gaps, and separations from the structure. There may be no vapor retarder strategy at all that could have prevented the problem.

  3. jkmurphy1 | | #3

    Thank you for your responses. I would have to agree with David. A vapor barrier would not have prevented this problem. The integrity of the envelope was compremised by the voids being present. When you have these voids between the foam and substrate, the product does not perform as inteneded. The air gaps we are speaking of were primarily where the foam had seperated from underside of the roof sheathing (OSB), anywhere from one inch to several inches. Since this problem, we have done extensive research on spray foams and their performances. There is a product called accuvent ventilation systems for cathedral ceilings. This allows you to get the benefit of the foam, but keep your roof deck ventilated from soffit eaves to ridge vents. It is very interesting how many spray foam contractors are now using a vented system with spray foams on a roof deck.

    One other thing I would like to know, can this problem exist with closed cell foam or is it an open cell foam problem. If anyone has any information, please contact me. [email protected].

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