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slab on grade insulation requirements in zone 6 upstate NY

user-7694189 | Posted in General Questions on

slab on grade, single story, new build 1700 square foot home- just picked up the plans from my architect and he says I don’t need insulation under the slab only at the edges?!?

I’m aiming for a net zero energy home, building with R30 ICF blocks and european tilt-turn windows- curious what the group thinks my slab insulation should be?

considering using Glavel or foam, just not sure what R-value I should be aiming for- and don’t want to disqualify my house right off the get go with the slab.


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  1. crawfordesquire | | #1

    i'd tell your architect he's right- you don't need subslab insulation.
    you're building a new house. need is irrelevant. you're doing what you want within the realm of the budget.
    i'd do 5" eps in climate zone 6.

  2. Eric_U | | #2

    I am mid-build of a barndominium in Central NY, Zone 5, and that is what my blueprints spec'd out as well. Just 2" foam board 4ft down around the entire perimeter. I like to overbuild though so I made sure to bring that foamboard up to the top of my skirtboard, and then also put R16 down on the ground before I poured my slab so there is absolutely no thermal bridging from ground to house anywhere

  3. Expert Member
    Michael Maines | | #3

    I design efficient homes, including net zero homes, in CZ6 and use anywhere from R-10 to R-40 under slabs, but usually find around R-20 to be the sweet spot. I use energy modeling to help me determine what insulation level is best. I can't imagine designing a slab-on-grade home in CZ6 without sub-slab insulation, even if net zero energy wasn't a goal.

    Shameless plug, you might find the book I co-wrote to be helpful, since we wrote it primarily for people in your position: I make almost nothing from it so it shouldn't count as promotion. The owner of this website was the original publisher, and the concept was developed here on GBA.

  4. Trevor_Lambert | | #4

    Completely off topic to your question, but if you care about being green, and it sounds like you might, ICF is one of the worst wall designs. Foam is one of the worst insulation types from an environmental perspective. Sometimes it's necessary, but in a wall it's definitely not. And concrete is absolutely horrible as well. You kind of have to use it for a slab, but it's not needed in a wall. In addition, both concrete and foam are expensive compared to almost all alternative materials.

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