Insulation and vapor barrier questions for a basement wine cellar
I am looking to convert an unused room in my basement into a passive wine cellar. I live in Zone 5 in BC, Canada. The 11′ x 8′ room has two exterior foundation walls (concrete), and two uninsulated interior walls finished with drywall. My house is well built by a reputable builder, and I assume the two exterior foundation walls are properly insulated (I have not removed the drywall to see). The floor is uninsulated concrete with vinyl plank. My plan is to simply insulate the two interior walls and ceiling (to R15 or higher) and leave the two exterior walls as is. I have investigated spray foam, but want to keep costs a little lower than the quotes I have received, so am thinking fibreglass batting. I have a couple questions:
1. Do I need vapor barrier on the outside of the interior walls — and if so can I wrap it around the studs on the inside of the room? That allows me to only tear out the drywall on the inside.
2. Is my plan to leave the exterior walls as is okay?
3. Should I just buck up for spray foam?
Thanks in advance for any advice!
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Replies
I can’t claim to be an expert on wine cellars, but isn’t it desireable to maintain higher humidity levels inside for cork preservation?
I don’t think you’d need spray foam, but rigid foam on the cellar-side of those interior walls, as well as the ceiling, would probably be your best/safest option. For the exterior wall, maybe just paint it with block fill paint (which is different from waterproof coatings) to make it look nice.
Bill
Thanks Bill. I'm less concerned about humidity but want to keep a steady temperature. My hope is that with insulation and a exterior door the room will stay between 15C and 17C but my concern with that is if I will get water vapour in the walls that will cause me problems.
Temple,
You're not going to have significant vapor drive through the partitions because there isn't a strong temperature difference across the wall assembly. Your aim should be for airtightness. Choose materials that aren't affected by damp conditions. You don't need spray foam -- mineral wool or fiberglass, carefully installed, will work for the partitions. You could add a layer of continuous rigid foam if you wanted.
That is the kind of answer I was hoping for Martin. Thanks! I am inclined to go with mineral wool/fiberglass at as high an R rating as I can fit.
Other than an exterior door and finished drywall with latex paint, what other strategies can you think of for airtightness? I will chink and fill gaps etc, but are there other techniques or products?
For batt insulation, airtight drywall is your best bet. Be sure to check the article Peter linked: it advises against using paper-faced drywall due to potential mold issues. Similarly, using lime plaster instead of paint will limit mold growth, while still acting as an air barrier and giving you a more traditional wine cellar look.
If you end up using rigid foam, taping the seams is an easy way to ensure airtightness.
Joe L. did an entertaining and educational paper on wine cellars for the ASHRAE journal. Here's the link: https://buildingscience.com/documents/insights/bsi-010-wine-cellars
Peter,
Thanks for the link. It's an interesting article. Joe's advice is to insulate the partitions with two layers of foil-faced polyiso with staggered seams. [Later edit: My mistake. See correction below.]
Martin,
I believe you have misread Joe's article. His advice for wine cellars is unfaced XPS with staggered and taped seams, or spray foam. The foil-faced polyiso is his recommendation for steam rooms and saunas that he places at the end of the article "Just to mess some of you up" :p
Aedi,
Thanks for the correction. You're right, of course.