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Community and Q&A

Conditioning and Ventilating an Attic

Benoit2000 | Posted in General Questions on

Hi all, I’m a new home owner in Sarasota. I’d like your advice on conditioning my attic and upgrading the ventilation. I’ll list some particulars about my current situation, and then the order of steps I’m thinking to fix it, but I’m no expert. If anyone knows a contractor I could hire to execute this for me, please let me know.

Current situation:

Home: 1,500sqft concrete block home in Sarasota.
Roof: 3/12 pitched shingle roof covers most of home, but I also have a flat bitumen roof that covers the master bedroom, lanai (screened-in outdoor area), and part of garage (not conditioned). Both roofs due to be replaced.
– Attic: vented with blown-in insulation on the attic floor, put in 2010. Plumbing and venting goes through this space, which is insanely hot in summer. I hear rodents from time to time running around up there.
– HVAC: a 3 ton 14 seer 36,000 BTU single-stage heat pump (installed Oct. 2020). Package unit outside of house. I use a portable 50-pint dehumidifier.

My rough plan to condition attic and increase comfort:
Step 1:
Roof: replace the pitched roof with a 24 gauge striated standing seem roof. Replace the flat roof with a GAF Polyiso Taper System, 60 Millimeter TPO. I tried to talk to a couple roofing companies about adding insulation to the pitched roof, but none of them do that. It’d be a challenge (impossible?) to try and coordinate a roofing & and insulation company in this area right now.

Step 2: Insulate pitched roof directly underneath roof sheathing. Remove the blown-insulation first. Then, use aero-barrier to air seal the attic. After that, my preference would be to install mineral wool BATs against the roof sheathing, but all the companies I talk to steer me to open-cell spray foam. They look at me like I’m crazy when I suggest closed-cell. I’m concerned about dealing with leaks with a spray-foamed roof.

Step 3: commission a Zehnder ERV along with whole-house dehumidifier (like Matt Risinger did).

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Replies

  1. Walter Ahlgrim | | #1

    The way I see it the smart move is to get the ductwork out of the attic.

    It sounds to me like you want to have a "conditioned attic”. If you can’t bring yourself to call it a conditioned attic it seems unlikely you will be able to bring yourself to heat and cool the attic making the attic likely to turn into a mold farm.

    When you move the insulation from the attic floor the roof line you double the surface area you need to insulate and double the area that will be losing energy. To add insult to injury moving the insulation to the roof most often forces you to choose expensive insulation types, often the dreaded spray foam. In order to control cost they often end up with a lower R value than when they started. Generally people end up adding registers to the attic in order to keep the humidity low enough to keep mold and rot at bay.

    The benefits of a conditioned attic are marginal at bests for single story homes with flat ceilings.

    Seem to me an EVR in your climate will always be bringing moist air into your home while you are desperately trying to remove moisture from your home.

    I am guessing this is an older home and far from meeting a passive house air change value with little need for more Ventilation.

    Given that most of the time the temperatures difference between indoors and outdoors is relatively small less than 30° there is little energy to recover.

    You did not tell us the R value of your current insulation.

    Walta

  2. Benoit2000 | | #2

    Thanks Walter - and yes, I do want a conditioned attic!
    I am very concerned about humidity everywhere. I said I will be getting a whole-home dehumidifier, and I would have that dehumidify the attic space as well.

    I don't know current R-value. It's a 1971 build. I don't think there's *any* insulation under flat roof, which covers master bedroom. I think it's just a plywood roof covered in modified bitumen.

    My main desire to condition attic is so that I can seal off the vents and other areas where rodents get in. I think getting rid of the blown-in insulation + air sealing will also improve IAQ.

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