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Homemade walk-in cooler

user-4421987 | Posted in General Questions on

I’m about to build a 10’x14’x8′ cooler for my farm, using a 24,000btu window unit and a CoolBot to reach a temperature of 40-45F. I’m using layers of 2″ eps rigid foam with foil backer (it was the best deal I could find on Craigslist) to reach a minimum of r-25 throughout, and 15 mil plastic as a vapor barrier.
First question: should the insulation be on the interior of the framed walls and vapor barrier over the insulation, or vapor barrier then insulation.
Second question: is there a way to build a foundation below grade–to avoid any steps– without pouring concrete?
Third: am I going about this wrong?

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  1. GBA Editor
    Martin Holladay | | #1

    First of all, the foil layer on the EPS is a perfectly adequate vapor barrier. What you need here is a good air barrier -- there is no need to worry about an additional vapor barrier. Every step of the way, you need to think about how you are creating an air barrier, and whether the air barrier is continuous (uninterrupted).

    You might, for example, tape the seams of the foil-faced EPS. As long as you do a careful job, and as long as you address all penetrations in your air barrier with some type of tape or sealing method, this approach can work.

    If I were you, I would put the rigid foam on the interior side of your wall framing.

    Q. "Is there a way to build a foundation below grade--to avoid any steps-- without pouring concrete?"

    A. Certainly. The easiest way is probably to use CMUs (concrete blocks), but you could use stone and mortar if you really wanted to. Unless you want to get very creative, though, these two approaches would still require a concrete footing.

    Q. "Third: am I going about this wrong?"

    A. No. But if you are unsure of the construction details, that may be a sign that you don't have much construction experience or knowledge. We can't determine that over the internet. If you are confident and experienced, you'll be fine. If most of these details are new to you, you may want to get some help from an experienced contractor or friend.

    -- Martin Holladay

  2. user-4421987 | | #2

    Martin, thank you for taking the time to respond. I should have prefaced my post by saying I have little to no construction experience, but I fool myself in to thinking I do because FHB is my favorite read.
    Reaching out for help is good advice.
    Q: Building on a budget, will 4' of eps get me to r-25 or should I add a thin layer of polyiso or even fiberglass behind the eps? Fiberglass doesn't normally perform well on coolers.
    Thanks again

  3. GBA Editor
    Martin Holladay | | #3

    Q. "Building on a budget, will 4 inches of EPS get me to R-25 or should I add a thin layer of polyiso or even fiberglass behind the EPS?"

    A. EPS can have an R-value as low as about R-3 per inch to as high as about R-4 per inch. So 4 inches of EPS will have an R-value of about R-12 to R-16. It will certainly be less than R-25.

    If you want R-25, install thicker rigid foam (either EPS or polyiso). Don't use fiberglass batts for a walk-in cooler.

    For more information on this issue, see Choosing Rigid Foam.

    -- Martin Holladay

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