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  1. #1
    Join Date
    Jun 2010
    Posts
    1

    Question Spray foam insulation in attic

    I live in San Antonio TX area and it gets really hot and sometimes really cold here. I recently bought an older house (1980's), which has composite shingles and R-19 fiberglass batt insulation in ceilings.

    I have had two foam installers look at the house and both have recommended a "sealed attic" approach with all vents (soffit and gable) being sealed up. They talk about the attic becoming a conditioned environment which would also help avoid heat/cold transfer issues for the duct work and air handler which are located in the attic.

    I am concerned sealed attic concept may cause moisture issues and is contrary to past wisdom of a well-ventilated attic.

    Any thoughts?

  2. #2
    Join Date
    Mar 2008
    Location
    nova scotia, canada
    Posts
    1,522

    Default Re: Spray foam insulation in attic

    theoretical the sealed attic should work as no moisture will be able to get into the space,

    however with my trade experience, and working with spray foam installers, the product does off gas. depending on the accelerant... some are gas based, some are water, icynene uses water as is propellant so its more safe, however the offgasing has no where to go so it basically will get trapped up in the space.... it also begs the question with no ability to breath will the roof framing become susceptible to dry rot..

    this method is still new and building scientists agree with it, but only time will tell if it truly works or doesnt
    fire up the saw and make some dust

  3. #3
    Join Date
    Mar 2009
    Location
    OKC
    Posts
    247

    Default Re: Spray foam insulation in attic

    We used open cell foam and sprayed the rafters and walls last winter, so far it has worked great. you need to make sure you have good ventilation in all of your bathrooms, and make sure nothing vents to the attic (ie dryer, bath vents), and we used 90% furnaces, which i think is necessary.
    HOPE THIS IS HELPFUL!

    Oklahoma City, OK

  4. #4
    Join Date
    Jun 2007
    Location
    Keyport, NJ
    Posts
    36

    Default Re: Spray foam insulation in attic

    What these installers are suggesting is called an unvented roof assembly. Buildingscience.com has several articles on their website that talk about them.

    I'm not very familiar with the climate in TX, but typically, the concern with moisture in the attic is from warm moist air rising up and condensing on the bottom of the cold roof deck. The spray foam will act as a vapor retarder when it is sprayed at least 2" thick. Some moisture will pass, but not enough to condense.

    I don't know enough about dry rot to comment on it, but if there is a way for the moisture to leave the wood, then there must be a way for it to return.

  5. #5
    Join Date
    Mar 2008
    Location
    nova scotia, canada
    Posts
    1,522

    Default Re: Spray foam insulation in attic

    i was looking at one my jobsites, which was just spray foamed, the insulators installed through vents in the rafter bays hard to the sheathing in all bays right up to the ridge, from there they spray foamed, same as regular inslation, key thing is to make sure there is airflow under the roof deck so the osb can breath at least
    fire up the saw and make some dust

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