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Community and Q&A

Walk-In Cooler Wall

Mstad16 | Posted in General Questions on

Building a 24×25 building, with 24×15 of that space being a walk in cooler. Don’t have much construction experience of conditioned buildings, but many google searches have brought me to this site, so thought i would just ask my questions here.

Have found little specific information online about proper cooler construction as most are pre-fab panels that are cam-locked together. The main advice I am working off is from a company we looked into buying a cooler door from. He said to make sure we put a 10-15 mil vapor barrier on the outside and caulk tape the studs so keep that barrier intact throughout the siding stage. When I look for that material, it seems like that’s essentially vapor barrier for concrete, is that right? Somewhat co fused because we plan on using closed cell foam inside due to moisture issues in a cooler, but that would then put a vapor barrier on the cold side, right?

have basically 3 options for the wall:

1) 2×4 studs, sprayed 3″ full then put on another 2″ rigid foam inside
2) 2×6 studs, sprayed 5″ full
3) 2×6 top and bottom plate with 2×4 studs used as a staggered stud wall, then sprayed 5″ full

So the wall from outside to in would be panel siding, vapor barrier, osb, stud wall with closed cell foam (options 1-3 above), finished with corrugated metal on the inside.

Am I missing something with the vapor barrier? Is there an ideal wall out of my 3 options as I see it?

We are located in northern KS. Cooler would be set for 34 F, for produce storage, and would run 7 months out iofthe year.

Any help is appreciated, thanks.
– Mark

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  1. Expert Member
    1. Mstad16 | | #22

      Replying here because I didn't see the option to on your most recent comment, #21.

      I like this scenario best. We will plan on building the structure, lining the inside and spray foaming from the exterior before applying sheathing and siding to the outside. I know sprY foam is not the greenest route we could go, but it definitely seems the best to fill and seal all the nooks and crannies and the idea of batts anywhere in this assembly makes me nervous if any of the vapor barriers were misinstalled. But one follow up question to this:

      Our interior skin is going to be corrugated roofing metal. If at any point down the road we wanted to change things with the finish itself of the cooler, I don't think we would ever get that steel off the walls if spray foam was adhered to the back side. Would it be a terrible idea to housewrap the inside of the cooler between the studs and metal to allow for removing that interior skin if we ever needed/wanted to? With the corrugated metal it would mean there would be 3/4" raised ribs every 9" that would not actually be in contact with the spray foam. But the metal would be vertical and any moisture build up would have the ability to drain downwards if it did accumulate.

      1. Expert Member
        Akos | | #24

        I would run the corrugated by your health department first.

        I think separating the SPF from the corrugated metal can work provided there is good ventillation behind it to allow for any moisture to escape, similar to a rain screen behind siding.

        Relative humidity in coolers tends to be pretty high though, even with some airflow it might not be enough to dry the back side, I think adhering the SPF directly to the inside surface is a safer option. There are a lot of pole barns insulated with SPF directly over the metal skin, from my reading the metal can be peeled off if it ever needs to be replaced.

      2. Expert Member
        MALCOLM TAYLOR | | #25


        "With the corrugated metal it would mean there would be 3/4" raised ribs every 9""

        That not corrugated metal, it's ribbed - and that alleviates a lot of the concerns. I agree with Akos though - you should check before going ahead.

        1. Mstad16 | | #26

          Sorry, I've always heard the terms interchangeably. Yes, it would be painted, ribbed roofing metal. Our large cooler is lined with this and it's never been an issue, but I will do some double checking. Will also look into the foam adherence on metal.

          Really appreciate the help and advice on all this.

          1. Expert Member
            MALCOLM TAYLOR | | #27


            Here it would be fine as an interior finish. Confirm that with the health department., but I bet they will approve it.

  2. Expert Member
    Michael Maines | | #2

    I would wrap the outside of the framing with foil-faced polyiso foam and tape the seams. Vapor drive in a walk-in cooler is strongly from the exterior to interior most or all of the time, depending on outdoor conditions, and studs allow moisture to pass through. Adding a plastic vapor retarder such as 10 mil poly wouldn't hurt anything and might help, but I'd prioritize the foam insulation in this case.

  3. Expert Member


    Over the years I've built two of them for restaurants. My advice would be to build the walls largely independent of the ones for the building. This has a few advantages: It separates the requirements for the cooler from the differing ones for the building's walls, future-proofs the structure if you decide to alter that use down the road, and means any problems in the cooler don't affect the integrity of the building's structure.

    - Get a good idea of the size and requirements for the mechanical cooling system, which will probably be situated above the cooler. It will need access to air and a drain for condensate.
    - Build the exterior walls designed to dry to the outside, much as you would do anyway, with a well sealed, robust vapour-barrier on the interior, batt insulation, and a vapour-open exterior with rain-screen cladding.
    - Install a layer of 3" to 4" of EPS foam in the inside, and line it with plastic panels and sealed seams. You can buy these at commercial kitchen supply stores. These act as vapour-barriers, and provide a tough finished surface, but also allow the cooler to be cleaned, and meet public health standards. Pay particular attention to sealing between these panels and the finish flooring.

    1. Mstad16 | | #5


      I am slightly confused. Would this involve two stud walls? And the 3-4" of EPS is within studs of the interior non-load bearing wall?
      Or are you thinking only 1 wall and the EPS and panels are simply on the interior side and fastened to the studs?

      Our cooling unit with have an outdoor compress and the evaporator will be inside attached to the underside of the truss joists.

      1. Expert Member
        MALCOLM TAYLOR | | #6


        Just one stud wall. This eliminates both the vulnerable wood from the cooler walls and thermal bridging.
        So yes in a sense it isn't a completely separate wall system, but all the components of the cooler wall are located inside the outer wall's poly vapour-barrier.

        One other small point. Try and find a door with a slightly raised threshold. Low enough so you can wheel in a hand-truck, but high so the bottom sweep doesn't constantly touch the floor outside, collecting debris and failing faster.

        1. Mstad16 | | #12

          Does your response change any if our intent is to build directly on top of a concrete slab? It would be insulated, but we did not intend to have any other finish for the floor.

          Why do you recommend eps over xps?

          1. Expert Member
            MALCOLM TAYLOR | | #14


            No, sealed concrete is a great floor for a cooler. The only minor problem with building directly over a concrete slab is the thermal bridging where that slab extends into the other part of the structure not being cooled. I'm not sure whether it's worth incorporating a thermal break in the slab there or not.

            Functionally either insulation will work. Unless there is a performance difference, I typically use EPS for it's better environmental attributes.

        2. Mstad16 | | #16

          Sounds good on the concrete. A few more questions on actual materials to use:

          -Can we use corrugated metal roofing as the final interior siding of the cooler? It's much easier for us to obtain and seems a more durable finish than plastic panels, but wasn't sure if it can be sealed as well as the plastic panels you were mentioning or not.

          -As far as sealing goes, do you just recommend a certain kind of caulking for seams and the siding to concrete?

          -What needs to go on the vapor barrier to ensure a proper vapor seal when the fasteners from the interior siding is attached to the studs?

          -what kind of vapor barrier do we need for the interior of that stud wall?

          1. Expert Member
            MALCOLM TAYLOR | | #17


            There are a couple of difficulties with using corrugated steel.

            It is designed for exterior siding and the trim works by lapping joints to prevent rain. That leaves it open to both dirt and moisture in the cooler, and it would be difficult to seal effectively. That's not to say you can't use it, it just won't give you the smooth, cleanable surface typically used in coolers, especially at the joints.

            The reason I suggested plastic panels is that they eliminate the need to fasten through the foam, and can be held in place by adhesive. If you want to use the corrugate metal I'd run pt. strapping at the top, bottom and mid-span at the walls, to reduce fasteners.

            No special care needs to be taken to ensure a seal at fasteners through the vapour-barrier as long as they hit studs. I would suggest using 10 mil poly, taped and sealed at the perimeter.

        3. Mstad16 | | #18

          Have another question. With this system, what are the consequences of poorly sealed plastic/corrugated steel on the inside?
          If that interior paneling was poorly sealed, would EPS or XPS hold up better? I know they are both closed cell, but EPS does have some texture to it, wasn't sure if that mattered.

          1. Expert Member
            Akos | | #19

            A fridge is essentially the opposite of a cathedral ceiling in cold climate. What you have to worry about is warm moist air in the summer time condensing on any cold surface. You can read this article here and simply flip the inside and outside around:


            To deal with this, you have a couple of options. You can put a sufficiently thick rigid insulation for condensation control inside your cooler, this is how typically these are built with the joinable panel sections. Outside of the panels, you can have standard wall with batt insulation.

            The facing on any of the foam panels needs to be directly glued to the panel, you don't want any gaps between non permeable layers as moisture can get trapped and create mold.

            You can skip the panels and go with spray foam. The spray foam needs to be applied not to your outside wall sheathing but to your cooler's inside skin. Again, any gap between the spray foam and the inside surface is a place with no drying potential where mold can form, thus the need to adhere the spray foam to the inside skin.

          2. Mstad16 | | #20

            With your spray foam scenario are you saying the same as Malcolm, build a wall with batt insulation and a vapor barrier on the interior, then spray foam? Sorry, not following what the cooler skin is and is not.

            Not to beat a dead horse, but what is (or is there) the issue with closed cell spray foam straight in the stud cavities and then rigid foam inside that over the studs to reduce thermal bridging?

          3. Expert Member
            Akos | | #21

            Your cooler will need an interior surface of some kind to meet local health regulations. This is either stainless or plastic but in either case it is a true vapor barrier.

            If you are spray foaming, the foam needs to adhere to this skin. So for example if you build a stud wall structure, you line the inside with stainless/plastic. From the outside, you spray foam against this surface. Your outside siding and WRB goes on after the spray foam.

            The only way to mix spray foam and rigid insulation is to use pre made insulation panels. These get attached to the inside stud structure and you apply the spray foam the same way as above directly to the back of the insulation panels. You want to avoid an air gap between two impermeable layers on the cold side of your assembly.

            In the above interior insulating panel assembly, you can always swap the spray foam for batts provided the insulating panels are sufficiently thick for condensation control.

  4. Mstad16 | | #4


    Would having my osb sandwiched between the foil faced polysi on the exterior and the rigid foam within the stud wall create issues?

    Could the siding (lp smartside panels) go directly on the foam?

    If we decided on the foam and vapor barrier, does the 10 mil poly go on top of or behind the foam?

    The overall building is 24x25, but only 24x15 would be the cooler and 24x10 would be additional storage, at this time, probably unconditional space. I know I would want to insulate the dividing wall the same as my exterior walls on the cooler side, but how do you handle the foam/vapor barrier on the dividing wall? How does that get tied into the exterior to create one single envelope for just the cooler portion?

    Should also mention the cooler portion would have a flat roof. My thought was to attach the corrugated metal on the underside of the trusses (just on the cooler side) and spray foam from above to desired depth as insulation and vapor barrier. Would that be correct?

    Again, sorry for all the questions. Have built and worked on sheds and garages, but never dealt with conditioned spaces.

    1. Expert Member
      Michael Maines | | #7

      I'll change my response to say that I agree with Malcolm. It's the opposite of a putting all insulation on the outside of the framing in a cold climate, which keeps the framing warm enough to prevent condensation and resulting microbial action.

      This is a challenging project to get right. I know several farmers and have seen what happens when walk-in coolers are not built with a good understanding of building science. I don't have enough first-hand experience with them to be able to provide thorough answers for you.

  5. walta100 | | #8

    General used factory made walk-in coolers tend to sell for well below the cost of material required to field build a cooler. I say find a used cooler buy a new refer unit and build a building with room enough for the cooler you find.

    Are you prepared for the bills that come with a walk-in cooler? Understand residential HVAC companies are unlikely to touch this type of equipment and commercial companies generally refuse work at residential addresses and generally charge 50% more per hour. My wild guess is a cooler that size at 35°is going to use $50 a month in electricity. Will you buy the insurance policy to cover the contents in the event of power or equipment failure? Most coolers that size end up with a remote monitored temperatures logging alarm system.

    Note anything this large seems likely to be commercial business requiring the local health departments approval and a field-built cooler seems unlikely to meet the requirements.

    You may well end up running year round to keep it from becoming moldy.


    1. Expert Member
      Michael Maines | | #9

      Walta, this is a common solution for the cooling equipment:

    2. Mstad16 | | #10

      We are a large farm that does both retail and wholesale business. For the wholesale side, we have an existing field built cooler (30x40x12) with two large industrial cooling units and our local HVAC is able to service and get parts for us. It is going on 15 years and have not had any sanitation issues yet, having no trouble passing annual inspections. It was built before my time here, but as i understand it it is exterior metal, spray foam, interior metal. Not sure if any vapor barriers were used or not. We only run that cooler down to 50F.

      We had a 10x20x10 pre-fab unit with the cam lock panels. It was already used when we purchased it and moved it to our farm in the 90s. Due to its age and being too small for our growing needs, we tore it down and are starting from scratch.

      After getting bids for a new camlock style panel construction, we decided to go the field built route. For a cooler this size it would need to have an outside structure to support it anyways. By the time all that is factored in, it is definitely cheaper to build ourselves with the added benefit of being more customizable for size and layout.

      But, at the end if the day, cost is less of a concern to us than building it right and regretting a decision 10 years down the road. If a stick built cooler can be built and vapor and moisture issues can be controlled, that is what we want to do.

      1. Expert Member
        MALCOLM TAYLOR | | #15


        One of the two I built was exactly that - a used manufactured cooler set into a building I had ready. Between the problems of sequencing the construction, and what you got compared to a site built one, I'm also not sure there is much to be gained going the used route.

  6. artisanfarms | | #11

    I have to second the recommendation to look for a used cooler, or used cooler panels. When I was farming, I purchased several walk-ins for much less than the cost of building materials to make my own. I would consider pouring an insulated slab, setting the cooler on it and building a shed roof over it and calling it a day. This will likely be your cheapest solution and if Kansas has ag zoning anything like NY's, you won't have any issues with the local building department.

    If it was bigger, I'd look at a sprayfoam insulated pole barn. A neighbor has a foam insulated pole barn that is at least 40x60x16 that he uses for veg. storage and staging for shipment and it works well.

  7. Mstad16 | | #13

    If we got a pre-fab unit we would side it and roof it to match our other buildings. By the time you do all that you might as well have just built a building and sprayfoamed it. In our situation, would easily save 1/3 the cost of a new pre-fab unit.

    So that was our intent and plan and before pulling the trigger on that just wanted to verify it wasn't bad building practice in the long run as far as moisture goes.

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  9. brooksbend | | #28

    I just built a walk in cooler with 5” used foam panels—seems to be polyiso faced with sheet metal on both sides—that I timberlok’d to 2x4 framing that sits on an insulated concrete slab. We sealed the gaps inside where the panels meet the studs with spray foam and now in figuring out the inside walls realize I may have screwed myself. Was going to put poly up and then plastic panels but that would mean a wooden wall assembly that would not be able to dry either inside nor outside.
    Am I screwed already or may there be something I could do to keep condensation out of the wall assembly?

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