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Passive wine cellar with XPS - condensation problem

10 years ago

I am building a passive wine cellar in a basement cold room in a zone 4a Northern region (winters −34.4 °C (−30 °F) - Summers +35 °C (+95 °F).

The cold room is 9’ long by 5’ wide with 8’ walls. It is located in the middle of the north wall of the basement. All walls are concrete. The north and east walls of the coldroom are exterior walls that extend 7’ below grade. The south and west walls of the coldroom face the conditioned basement and have R7 XPS foam on the conditioned basement side. The concrete ceiling of the coldroom is the 2’ thick concrete slab that forms the exterior entry stairs. There is a bare concrete uninsulated floor. There is an outdoor insulated door (R10) that is in the middle of the south wall for access to the basement.

Image gallery is here:

I purchased used 4” XPS insulated foam (Roofmate) that is R20 ( and has ship lapped edges.

I started with 1 layer of the 4” XPS over the ceiling and then covered all the walls with 1 layer of 4” XPS foam leaving 1’ of bare concrete at the floor on the exterior North and East walls). I left the entire floor bare. I then sealed all seams with low expansion foam. As overkill I then used tuct tape ( to tape over the foamed seams (HUGE MISTAKE �" the adhesive has a huge odour and I have had to disassemble all the walls to remove the tape because it stunk so bad). I then placed a 2nd 4” layer of XPS on the ceiling to make it R40. I then built a 2x4 pine stud wall around the interior that I was planning on leaving bare simply to form a structure to attach my metal wine racks too. With this setup temperatures were 15 °C (59 °F) with 70% humidity.

I waited 2 weeks to see if the smell from the Tuct tape would dissipate but it never did so I took down the stud walls and removed the 2nd layer of XPS foam on the ceiling and removed all the Tuct tape that was covering the seams.

Here is where the problem comes in. On the inner layer of XPS on the ceiling, where I had put low expansion foam on the seams and covered the seams with Tuct tape �" there was a lot of moisture condensation on the Tuct tape at each seam. Somehow, warmer, moist air is gaining access to this interior layer and there is enough temperature differential at the seams to cause condensation. I only disassembled the 2nd layer of XPS foam on the ceiling to get at the Tuct tape, I left the single layer of foam on the ceiling and walls so I do not know if the bare concrete behind the foam is weeping as well.

So what should I do?

1) Should I cover the bottom 1 foot of the North and East exterior walls instead of leaving them bare like I did currently? (It is possible that some warmer air is infiltrating behind the foam wall panels and migrating up, it may be better to just have a solid wall of foam from floor to ceiling).

2) What do I do about the foam sandwich on the ceiling? I am really surprised to see condensation there because I have R20 with all seams sealed by expanding foam then a 2nd layer of R20 with all seams sealed by expanding foam but somehow warm moist air is getting between the 2 layers. I have removed the tuct tape so it is possible that the seams may breath a bit better (though with sprayfoam in the seams I don’t understand how there is any air movement at all).

With the R20 foam walls and R40 ceiling I was not planning on finishing it any further. I was going to have bare pine stud walls for structural support of the metal racks but was not going to finish it further than that as the blue walls don’t bother me and no mold will grow on the foam. I know the ideal thing would be a sprayfoam installation but I have insulated this whole 9’x5’ space for under $300 using the recycled foam. 4” closed cell sprayfoam on the walls with 8” on the ceiling would cost me about $1400.

Any ideas? I don’t want to move my bottles into this room until I am fairly certain that mold is not going to be an issue but with winter coming and the furnace going I want to get my wine to a cooler, more humid location ASAP.

(note in the photos you can see pink insulation above the door. This area was closed off with foam as well. I had tuct tape there too so I had to take it down which is why you can see it).



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    MAC Design + Build
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    Loudon County Full-Service Design/Build Firm & Kitchen Remodeler