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Community and Q&A

Is open-cell foam good/bad sprayed on the underside of a roof in Connecticut?

Josh Ayers | Posted in Energy Efficiency and Durability on

I am wondering if open-cell foam (specifically Icynene) is OK to spray on the underside of a roof deck of an unfinished attic of a 1920’s home in Connecticut.

The attic is a walk-up attic from stairs in a bedroom. The house has a basement which is where the boiler is located and there is no air conditioning. The walls have all been done with the closed-cell pour formula from Icynene.

I am asking this question because the attic has been sprayed already and I have had problems ever since. I have had a lot of moisture sitting on the surface of the Icynene in the attic in the summertime as well as on the brick of the chimney that runs up through the attic.

I have cedar shakes for siding on my house and have also noticed that the paint has started to peel off ever since the insulation was done on the house and have also had woodpeckers attacking the side of my house now. I don’t know if any of this is related or not but any help would be much appreciated


  1. GBA Editor
    Martin Holladay | | #1

    If the spray-foam installer did a good job, there shouldn't be any reason why you couldn't install spray foam on the underside of your roof sheathing in Connecticut.

    In your climate zone, it's a good idea to spray the underside of the cured foam with a vapor-retarder paint, to prevent moisture accumulation in your roof sheathing. Most building codes also require that the cured foam be protected with a thermal barrier (for example, gypsum drywall) for fire safety.

    Ideally, the foam should be thick enough to provide at least the minimum R-value required by the building code. The 2009 IRC requires a minimum of R-38 insulation for ceilings in your climate zone; that's about 10 1/4 inches of open-cell spray foam.

    If you are seeing moisture condensing on surfaces in your attic during the summer, the interior of your house probably has elevated humidity. You should investigate what the source of the moisture is. Typically a basement or crawl space may be responsible. The solution to this problem may require modifications to your basement or crawl space. You may also need to operate a dehumidifier or air conditioner during the summer.

    It's certainly possible that adding insulation to your walls will shorten the life of paint on your siding. This is an unfortunate side effect of some insulation jobs. One possible solution is to install WedgeVents.

  2. Aj Builder, Upstate NY Zone 6a | | #2

    Josh, look into moisture sources and start using humidistats. Read up on high moisture problems sources and solutions. People, showers, lots of indoor plants, wet basements, high humidity basements..... Etc. Dripping condensation is way beyond normal.

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