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Should the entire top plate along with the adjacent 2 inches of drywall be covered with open cell foam in my foam insulated attic?

suect | Posted in General Questions on

I have posted a few questions on a totally open cell foamed Attic in Texas in hopes of findOmg the source of humidity in our attic.  I have consulted with contractors but most are interested in full insulation work vs fill in type jobs.  I appreciate all the advice that has been given.

The RH levels are going down but the humidity still remains higher during the day vs at night (55% day/51% at night).

I have noticed the top plate is exposed with insulation filling in the top corner where it meets the outside wall, but rarely is it totally covered.  I am also able to see where the drywall and the top plate meet throughout 90% of the attic.   Would this be done by design or would insulating this be best practice?

Thank you

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  1. Expert Member
    ARMANDO COBO | | #1

    Where in TX? Is this a conditioned attic? Are there any ducts and equipment in the attic? How long ago was this attic sprayed?

    1. suect | | #2

      San Antonio.
      The attic is semi conditioned from leaky ducts. No dedicated supply. Just a return that was sealed when found (behind HVAC system).

      All ducts and HVAC are in the attic. And the home is 9 years old, the insulation was sprayed at that time.

      Where the ceiling meets the outer wall in the attic is the concern for another penetration. (I may have used the incorrect term).

      In the summer humidity would be as high as 62% and temperatures up to 86 degrees. Lows at night of 46% Humidity and 73 degrees.

      Several HVAC contractors have advised to completely seal the ducts. (Due to temperature differences on the foam that could lead to moisture on the roof deck). Others say not to and keep both living space and attic the same. Very confusing.

      I’m wondering if there are outside penetrations that are causing the swings.

      I welcome your thoughts on this.

      Thank you!


  2. Expert Member
    ARMANDO COBO | | #3

    Here are a few comments:
    My go to conditioned attic, in TX, for metal, clay or flat roof assemblies is 1.5” iso on top of the roof decking and 8”ocSPF under the roof decking. For shingle assemblies is 2”ccSPF and 8”ocSPF. If I had to guess, a typical installation in TX, and large parts of the Country, is 5.5” ocSPF under the roof decking and that’s it.
    Insulators con builders into such installation because it would be allowed under the performance code, but must builders don’t follow up with hiring Raters and Verifiers to do what Performance Codes requires them to do, and is also cheaper. Also Builders, most of the time, have no clue about Codes, and since here in TX there is no licensing or education requirements, then is homeowner’s open season all year round. It’s a sham!
    Not only that, but most importantly, the laws of physics and chemistry DO NOT CARE about Codes, its applications, materials or bad building systems.

    Here are some thought about your case:
    1. Humidity readings in the 60s are no good, the good thing is that they go down in the mid-40s at night, so it’s not a long time issue. We set up our HVAC systems to control humidity bellow 50%.
    2. Assuming your thermostat is set in the mid-70s, an attic temp of 86°F is high for a “conditioned” attic, so not enough insulation, unsealed penetrations, and a grossly oversized AC system that is not removing humidity, could be a bad combination.
    3. I think you do want to solve these issues, but I don’t think you have a critical situation, especially in the dry climate of San Antonio. However, here are some recommendations at this point: a) Seal attic, b) Fix AC system and provide supply vent in the attic. c) Install dehumidifier, after you fix first two, and at least until you control the humidity.

    A quick search on the subject, here at the GBA: There are many more good links.

    1. suect | | #4

      Thank you

      I will definitely read all the articles you sent and greatly appreciate your expert feedback and welcome future comments

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