Hi all. First, I apologize to any of you that have been following my saga on cellartracker. I know you are tired of hearing this story. (I’ve been posting and researching this project there for well over a year.) I’m looking for some advice on improving my passive cellar.
The temperature and humidity swings are out of control. It gets up to 72 F (and over 95% humidity) in the summer and it’s currently hovering around 50 F (65% RH) with the outside temperatures in the 30-40 F range. I live in Fairfield, CT if that helps you figure out the climate.
The space is challenging. It is about 28 feet long, 4 feet wide, and 8 feet high. The builder happens to live across the neighborhood, so I’ve been able to ask him some questions about it. When the house was built (1998, I think) this area was created with the intention of making it a natural wine cellar.
All four sides are concrete. The front wall and left side walls are below grade - except for the top twelve inches or so. The back and right side walls border on the remainder of the (finished) basement. All four walls are concrete foundation walls. This is because the cellar is not actually under the house. It lies under the front (stone) porch - the stones sit atop a wood frame of 2 x 4 and plywood. The cellar floor was never cemented. It is just the coarse gravel that lies beneath the rest of the foundation.
Since we moved in a few years back I spruced up the cellar while we were finishing the rest of the basement. It has a weather proof door, about 3-4 inches of closed cell spray foam insulation in the ceiling and pea gravel with stepping stones on the floor. On the finished basement side of the south wall there is more closed cell foam in the 2 x 4 frame. The finished portion of the basement is kept at a constant 65-70 degrees and 40-50% humidity.
I put together a rough Powerpoint diagram. I was hoping I could get away with just throwing more insulation on the walls, and maybe a vapor barrier. (I’m not sure where all that humidity comes from in the summer - the ground or the outside.) I could stick a vapor barrier under the pea gravel, but that’s more work than I want to do if it is going to prove unnecessary.
I’m no expert, and maybe someone with cellarbuilding experience (Chris Kravitz?) or better knowledge of physics/thermodynamics will speak up. But my guess is your biggest issue is that “except the top 12 inches” part. Concrete walls are not good insulators, and a foot means that about 12% of your wall is basically exchanging heat with outside. Plus you have to get down about 3-4 feet in ground before you get to a constant ground temp (probably low 50s around here). Anyway you can landscape to maybe bring up grade outside?
I have a passive cellar (in Westchester, so similar climate). Old stone foundation, top foot of basement also above grade (though basement/cellar floor a tad lower than yours, so a bit more heatsink). 2 walls face basement, I put foam insulation outside on one wall when I replaced steps, built up ground on other, and decided I could get by with 6’4" ceiling, so filled with insulation- so all exposed wall is below grade. Generally keeps it to 68 degrees at top in summer. Though I ended up putting a cheap AC in that I can run a bit in heatwaves (lowest setting is 64F, I didn’t tweak). I accept that I can get label damage from humidity, and that I might see more advancement than a 55 cellar, but wines seem to age well. Main thing is not quick changes.
You RH is coming from outside. Since the air outside is warmer in the summer it will hold more moisture and when exposed to the cooler area of your wine celler will show up as a higher RH. What you are seeing in the winter is the natural from the ground, and if it was fully sealed off from the outside should hover in this range.
Seriously though, passive cellars depend upon the earth to insulate them and this design doesn’t have enough natural insulation. Insulate any wall and ceiling isn’t below grade earth and you could reevaluate, but I have an idea that you need active cooling
Greg,
Dale is right. You are getting too much heat and humidity coming in from the outside-heat and cold from the walls/ceiling and humidity from everywhere including the ground. First, with an outdoor space above, that sun is beating down on the concrete and only 3 inches of sprayfoam- or around a value or R-19 is not enough. I would tell you to frame down the ceiling on the inside and add more sprayfoam to get a higher R-value. Plus, the top 4 feet of the walls are affected by the same temperature. You need to get sprayfoam in the walls as well. Lastly, check under the gravel and see if there is any vapor barrier. IF not, get some 6 mil plastic and line the floor with it and get more gravel on top of it. Unless your are completely below grade by 30" or more, I’m afraid that in your area, you are going to have a very difficult time with a passive cellar…
I’m OK with a temperature a little higher than 55F. I could live with low to mid 60s as long as it is pretty stable year round.
My plan right now is to drop the ceiling by another foot and add insulation along the outside walls and see where that gets me. I would like to throw a vapor barrier (even if it’s not entirely sealed) under the gravel, but that will take a lot of work. We’ll see how it goes.
Have any of you heard of Prodex? Seems like it is usually used for roofing, but has wine cellar applications as well.