Finishing off a Passive Wine Cellar

This post is my first so I hope posting this as a new topic is correct.

I have read several prior post on passive wine cellar construction and I wanted to ask the opinions of this community.

Quick background. I am 1 year into a newly constructed house that has a separate “wine cellar” room. Let’s just say my history with wine collecting basically has been matching supply to demand. With a Wine Cellar room, I have begun collecting a few cases of age worthy wines. When I first moved into the house, I thought you always need to use something to maintain the temperature and humidity in a wine cellar until I started learning about passive wine cellars. Hence what I think I have is basically the foundation for a passive wine cellar.

The wine Room is 10 x 20 with 9 1/2 ft ceilings. Walls are all cement and 9 1/2 inches wide. The door into the wine cellar from the rest of the basement is an outside metal door with a seal. One long wall faces east with the other long wall facing the rest of the basement…not heated at this point. I estimate maybe 18-24 inches of the room is above ground and rest below ground. The roof of the wine cellar is our front porch and per builder, the surface is 2" ledge-stone , under that it’s roughly 4" of poured concrete, under that there is #4 rebar spaced evenly and laid over galvanized “B” decking. So the ceiling in the Wine Cellar is that galvanized decking with one row of cinder blocks at the very top of the cement walls next to the ceiling.

I am located in Raleigh, NC. I have done limited testing but recently in February the wine cellar has ranged 50-55 degrees in air temp and 75-80% humidity. Right now using an infrared gun, the floor is 55 degrees and most of the lower walls are 55/56. Higher up closer to ceiling I get the 58/59 range. I do remember at one point last summer walking into the cellar and it was very warm. However, I might chalk that up to having my wine frig in the cellar and if it turned on, I am sure it warmed the room up. I have since pulled out the wine frig.

Sorry for the lengthy build to the question but trying to be thorough.

From everything I have read, I am thinking I need to insulate the ceiling and the whole one long wall facing the basement. Then insulate 4 feet down from the ceiling the other walls. Leaving what is left of 3 walls and the cement floor as my passive wine cellar cooling. I believe the high humidity now is due to the ceiling/galvanized roof not being properly sealed and hence once ceiling insulated, I am left with the natural humidity from the cement. (Not sure that is correctly stated but what I believe occurs.)

I am trying to get to a sensible first step in completing the space.

Thanks for your thoughts, Steve

You will realize a bigger cooling benefit by insulating all 4 walls and ceiling, leaving the floor as what provides the cooler temps. When I built my active cellar, the room was noticeably cooler than the rest of my basement when it was fully insulated and door shut (before the cooling unit was installed). The cooler temps came from the floor and I believe would have been cold enough to go passive if I weren’t bothered by temp swings and not keeping ideally 55* in the summer/fall. If you don’t insulate all 4 walls, your cellar will equalize at the temp of your basement, even with the insulated door. In fact, I doubt any utility of insulating just 1 wall by itself.

I do also doubt a wine fridge would raise the temps materially in a basement room that’s 20x10. If I were you, I’d insulate 4 walls and the ceiling and also leaving room for a cooling unit if you realize your summer temps are getting higher than you’re comfortable with. A few extra bucks on a unit beats the heck out of special bottles that were saved beyond their years.

Yes, insulate all the walls and the ceiling especially. The part of the cellar under the porch is likely the be problematic (as is the southern location in Raleigh) but you won’t know till peak summer arrives. If you can spray closed cell foam that will serve for insulation and the vapor barrier. You can remove the humidity easily enough with a decent sized de-humidifier.

I live in Chapel Thrill and having built 3 cellars now did not even try passive here. Passive worked for me in CO at 8000ft. But if you are just starting and do not have a slug of valuable wine for super long term storage this is fun to try. Try to plan for active cooling if you are likely to get serious about this at a later date.

Chris offered good advice. Insulate all but floor and accommodate later addition of artificial cooling. IMHO you need to monitor temps thorough the summer season and make sure they don’t get too much above 65 for any length of time.

My passive cellar stays between 56 and 63… but then I am in Alaska. [cheers.gif]

Good advice above about insulating walls and ceiling and leaving the floor uninsulated as a heat sink. However, in NC with only a partially below grade basement you may find temps too high in the summer. Not an emergency if the cellar gets into the 70s for a few seasons but if that happens, for long-term storage I would be prepared to add a cooling unit.

Thanks for all the inputs. I did have an electrician add a dedicated breaker and line for a possible cooler unit on that one wall adjacent to wine cellar. (This was done before I discovered that I might have the makings of a passive Wine cellar.) So I would just have to drill hole and the cooler unit would output to utility room.

I’m building a passive cellar in the Hudson Valley, where it’s substantially cooler in the summer than NC. I posted on my research in a thread earlier this year.

You’re right about the ceiling and basement wall being key. Like you, I was thinking of insulating the exterior walls only a couple of feet below the ground level and relying on the supposedly cool ground below that to maintain my temperature. But I concluded that I probably need to insulate the entire exterior walls, because:

(a) the ground gets surprisingly warm surprisingly deep in the summer and
(b) concrete is a fairly good conductor of heat and cold (even more with rebar, I’m sure).

Here’s a chart I posted in that thread showing how warm the earth can get. And this was for Western Massachusetts (the C and F are reversed on the top scale):

Be aware, too, that the floor slab will convey heat from the rest of the basement – something else I learned. That might be significant in your climate, particularly if your basement is not air conditioned.

My passive cellar in far northern coastal California has its lowest temperatures in February each year, and highest temps in September (about a 10 degree spread averaging 50 in Feb to 60 degrees in Sept). My concern in reading your post was that cellar temp in March was 58-59 in the upper reaches. I would encourage as much insulation as possible, and preparation for cooling in the summer. Let us see what it looks like when you are done. All the best, Jim

I live in Delaware and your cellar sounds almost identical to mine, just a touch larger. If you can, closed cell spray foam on all walls and ceiling. Your temp will be higher in the summer. Right now I’m at 55 degrees with 75 percent humidity with a cooling unit that never runs. At the end of summer I would not want to go one day without a cooling unit.

Please keep us updated. I intend to try a passive cellar in a basement area and would like to see your progress.

First of all welcome Stephen! Happy to have you posting. You’ll get a lot of advice from experienced folks here. Bad news is the advice is typically contradictory. [wow.gif]

Second, remember that insulation stabilizes; it does not cool. While insulation is necessary to ensure that you don’t experience harmful swings in temperature, it is of no value at all to bring down the temperature inside the cellar. To the contrary, it will aid in keeping your temperatures high in the fall just as it keeps your temps low as you transition from winter to spring. (BTW, a full cellar gives you thermal mass that helps in stabilization too, which is a decent excuse for buying more wine)

The only way to determine whether you will need artificial cooling is to test during the summer and fall. If you get into the mid-60s at peak, I think passive is the way to go (although it probably means your wines will mature a little faster, and perhaps a little differently, than wines kept at a constant 55). If the cellar gets up to 70 or above, I’d start to think about cooling alternatives

After years of “going passive,” I installed a small cooling unit (actually a room a/c with a fooler circuit) in my small cellar in VA. I usually turn it on in April at some point and off in October. Works like a boss and was cheap and (relatively) easy to install.

Good luck!

Given your location, I doubt very much that you will get away with no cooling unit.
If you just install an ordinary room air conditioner (without fooler circuit), you can maintain 60-62 degrees max all year round.
You will only have to use it in the summer.
You do need to fully insulate that room.


I built my passive cellar last year, in Maine. I agree strongly with the advice of everyone above to insulate all four walls completely, and the ceiling even more.

I would only add two things to the other comments.

First, though it has been alluded to, I can’t believe no one has specifically mentioned the Richard Gold book: How and Why to Build a Passive Cellar. I thought mentioning that was required in all passive cellar posts! Anyway, if you have not read it, read it. It’s dense, but full of useful info.

Second, pay attention to your door as well. If you do all the insulation everyone is talking about above, your door will be your weakest link. You will probably insulate to r 20-40, but your door will only be about r7.

I added insulation to the inside of my door in the form of foam board insulation. It is not pretty, so if your cellar is intended to be a show-piece, this may not work for you. But, if it is for bulk storage, it is an effective and easy solution. You can see in the pic below I used two pieces on my door. (I used two different types just because that is what I had.)

The door is the hardest part of my cellar design to select. Our home was built in the 20’s and I’ve hoped to build out the wine cellar in a way that it would appear to have always been there. I have all the materials selected except the door. I’ve looked at everything from a custom wooden door that would have insulation in the core to salvaging an antique walk-in cooler door. I really want to avoid the metal exterior door that many DIY cellars use but will definitely not go with the faux-old world wrought iron.

Anyone done a door other than the above?

Yes, that chart I posted to above was from Gold’s book, and I highlighted his book in the thread I linked to above. Essential reading, though he’s so obsessively thorough that it’s hard to find the takeaways at times.

Yes, an important point. What did you use to stick the insulation board to the door?

I bought an insulated wooden exterior door from the local building supplies place, with a frame and weather stripping. The R value wasn’t listed, so I figured I’d add some on the back, like Mark did.

John, did you use weatherstripping on the bottom of the door?

The weatherstripping was already there in the frame that came with the door. But that’s essential. I have used a friend’s passive cellar, which did not have weatherstripping, and there was a noticeable draft around the door. Not good!

FYI, door manufacturers and suppliers like Home Depot avoid listing R values on exterior doors, but the Dept. of Energy’s website says that most with an insulated core have R values of 5 or 6 – well below what you want for such a large surface area.

Welcome to the community, Stephen!

I did my passive cellar 18 months ago in the Chicago area. Followed a lot of advice from here and Gold’s book. Cellar position is similar to yours in that part sits below grade near a front porch of concrete. Spray foamed ceiling and all walls to make the floor the source of cooling, consistent with much of the above advice. In my first full summer last year, cellar got up to 66 (vs. winter where it rides at around 58). I just ordered a cooling unit and will have it in place going forward. Given your location, it is likely you will see upper 60s in the height of summer, even with insulation. Won’t ruin the wines of course, but starts to erode the value of having a purpose-built cellar. Therefore, I agree with others - you may want to put a cooling unit in from the start. Good luck!