Passive wine cellar with XPS - condensation problem

andrewzyticOctober 21, 2012

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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I tried to access your link & nothing happened could you please post a proper link?

    Bookmark   October 21, 2012 at 8:36PM
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2nd question I need to ask is there any venting in this room?

    Bookmark   October 21, 2012 at 8:39PM
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Sorry, which link are you having problems with? The works fine for me.

As for venting, no. It is a fully inclosed concrete box. Monitored humidity is a constant 70%.

For properties on the roofmate insulation see:

It's properties are better than XPS wallmate which can be used without vaporbarrier. I think my seams are just not tight enough.

    Bookmark   October 21, 2012 at 9:06PM
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You are going to have a lot of problems. You're sealing the concrete wall with the insulation?

"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)."
What's on the other side of the concrete? Dirt? Or is it an attached house like a row house?

If it's a detached house and it's just dirt on the other side, which seems to be the case because you said it extends 7 ft below grade, you will have a great deal of condensation and eventually mold. The concrete walls are not completely dry and sealing them the way you did allows no place for the moisture to go. Don't seal those walls off.

"As for venting, no. It is a fully inclosed concrete box. Monitored humidity is a constant 70%."

So the ceiling is concrete too and your entry stairs are over that? If so, no wonder you have condensation. On the other hand, you have the makings of a great wine cellar. I wish I had that.

Depending on where you are, the soil temperature can vary quite a bit between winter and summer but you're in a cool area so you should be fine.

If you have 70 percent humidity in the concrete room, why are you insulating with a vapor-proof material and then sealing off all possible avenues for the moisture to escape? You can't do that. What happens to the temperatures if you don't seal the ceiling and concrete walls and just insulate the walls exposed to the basement? I think you'd be far better off with that approach. If the concrete walls give you a stable temp, why insulate them?

Also - the door is R10 and the rest of the insulation is R20? If you really want R20, put insulation on the door too. Otherwise, you have a huge section of your wall that has a lower R value than everything else and you will effectively have insulation of R10.

To start, I would take down the insulation from the concrete and monitor the resulting temp in the room. It seems like you can actually get a pretty good temperature and perfect humidity with what you have, doing minimal work.

Good luck.

    Bookmark   October 29, 2012 at 2:15PM
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I have a very similar situation. My cellar is going under the front porch. It will be about 9' below grade. I am in Alberta, Canada so it is hot in the summer and very cold in the winter with very low humidity.
I was thinking of heating it on a seperate zone with my infloor heat and possibly putting a exhaust fan in hooked up to a humidty sensor to deal with any excess humidity.

I am going to spray foam the celing and outside walls with 2lb foam and likely batt and vapour barrier the warm walls. I am going to frame and drywall all the walls. I also want to put some form of stone (likely limestone) on the walls .

The floor will be left concrete. Likley will have it polished.

Any ideas or sugestions would be greatly appreciated. I can send a pdf of the basement drawings. I can't post a pdf.

    Bookmark   March 23, 2014 at 1:36PM
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