If you hope for a passive cellar, the exterior walls will serve to cool the cellar. I would not insulate. All surfaces exposed to the heated portions of the house should be insulated. Be mindful of vapor barriers and potential condensation issues.
The heat venting in the ceiling should be insulated. Better would be to insulate the entire ceiling since the space above is warm.
Hey Stephan, a few answers for you. You don’t need to insulate the outside walls if they are mostly underground. Make sure that window is sealed well and then use some reflective film on the inside of the glass and then put insulation over that. After you build the other two walls, use roofing insulation in them and the ceiling, as it has a higher R-value than the blow-in stuff. You can always test it out the first year and then get a cooling unit if it doesn’t stay cool enough. If you haven’t built a cellar before, do yourself a favor and get “How and Why to Build a Wine Cellar” by Richard Gold. And if you need recommendations for Portland wine shops, storage, etc., feel free to shoot me a PM.
My recollection from using the Gold book 20 years ago is that he would say to insulate all the walls and the ceiling, as this will give the floor the most influence over the interior temp, in terms of the outside temp not being buffered by insulation.
That makes sense to me, but how much cooler it would stay this way depends on how much of the exterior walls are below grade, how much sun exposure those walls and the ground outside them have, etc. In a relatively cool climate I might not bother if the exterior walls are fully below grade, and face north and east (especially if the eastern exposure is shaded by trees or the like).
You will get a more constant temp, and a cooler temp in the summer, if you insulate all four walls, than if you don’t. These other factors influence how much cooler and how much more constant.
Don’t assume the outside walls will help cool the space in summer. This was the biggest surprise to me in the Gold book.
Your basement is only partly below grade, and ground temperatures can get up into the high 60s even five or more feet below ground, depending on the locale.
Therefore, in the warmest months, the only surface that will be cooler than your cellar air is the floor. That means that, if you make the wine room too small, the ratio of floor surface to walls and ceilings will work against you in the summer.
Here’s Gold’s chart of ground temperatures, varying by season and depth. He bases this on Western Massachusetts.
What direction does your cellar face? If it’s anything but north, you will need to think about the temperature of the outside wall.
One of my foundation walls faces west and got some direct sunlight in the afternoon. I added large fiberglass planters, about 18" wide, against the exposed exterior of the wall outside my cellar. I put insulation board behind the planter and filled the planter with soil, hoping that would keep the temperature of the foundation wall, and earth against it, a few degrees cooler.
FYI, after a very hot month, my cellar in the Catskills is running a bit over 67F, as it did last year. The year before it topped out a degree or so lower. That’s higher than I hoped, but doesn’t freak me out.
I have a passive cellar in Virginia. Temp range is 55 to 65. Floor is uncoated (just the concrete) and I did 2x6 with Roxul insulation and a 2" layer of Thermax polyiso insulation all around. My outside wall is north facing, but only about 1/2 to 2/3 underground. It was enough to warrant insulating. The floor and ceiling are you biggest contributors though. Floor is a good heat sink year round and the ceiling will always want to bring the cellar to the house temp. That’s why I did extra insulation on the ceiling and zero on the floor.
I have a duct like yours but just stuffed the cavity with insulation and it seems to not affect anything. I couldn’t see where the duct was with my thermal camera from work during the winter.
Humidity goes as low as 60 in the winter and up to 70 in the summer. And I did rough in for a CellarPro unit should I decide I need to hold 55 all the time.
Oh, and I have Gold’s book. Used it a lot to plan for the insulation, vapor barrier, and ground-temp model.
Another tip I picked up somewhere and use is to put those interlocking foam “tiles” (the ones that connect like jigsaw puzzle pieces) on the floor, assuming you’re going for utility and not show. Eventually you’ll drop a bottle or some weird-shaped bottle will slip out of its bin or the like, and foam is much more forgiving than concrete.
Those are similar to mine – even a tad better than mine, and I’m in a significantly cooler area. Congrats!
I’m at 800 feet elevation, so it drops to the 60s most nights even in the summer. It’s cold in the winter, so my cellar drops to near 50F then.
Like you, I have 2" polyiso board behind sheetrock on the exterior walls. The inward-facing walls have 3" of fiberglass batts in the cavities, plus 2" polyiso board on top of that – something like R35-R40. I went all-out on the ceiling, with 6" batts and 2" polyiso on top.
Here’s a pic of my cellar during construction. The far wall is the north exterior wall with about 1 foot of exterior exposure at the top. I put 1" hard foam insulation on the concrete surface and held it in place with furring strips, then covered with sheetrock. The west wall is the same, except for a cellar well window which I sealed and used 4" of hard foam for insulation behind a removable piece of sheetrock in case I need to gain access to the window in the future. The two interior walls are 2x4 with R13 FG insulation. The ceiling is R30 FG insulation except where the heating duct fills the space between two joists. I added an inch of hard foam beneath the duct before sheetrocking. The door is an inexpensive exterior (back) door. I didn’t use a vapor barrier but probably would have been wiser if I did.
In winter the space will get down to the mid fifties on its own. Right now (late summer) the little (about 300 watts) cooling system I’m operating can’t get the space below about 63-64 degrees with air temp near the ceiling as high as 68 at times. The basement around the wine cellar varies between 75-78 depending on exact weather conditions. In September I expect the average basement temp to start dropping and the wine will get back to 60F by the end of the month.
The main reason the basement gets so warm is the east wall is ground level and we have a tandem garage space for two cars that isn’t isolated from the basement. In fact, the inner car is only 10 feet from the east cellar wall.
Again, very similar to my experience. The rest of my basement stays in the high 70s much of the summer, partly due to the boiler and hot water tank down there. On cool nights, I open all the basement windows to dissipate some of the heat. I’ve even left the basement door open on really hot days to let hot air flow up and AC’ed air go down to the basement.
Concrete is a pretty good conductor, so the ambient basement temperature in the summer keeps my cellar floor warmer (around 55F) than it would be if it were only the ground influencing its temperature.
Stephan-- That’s another factor to take into consideration, which I learned from Gold: The concrete floor will conduct some heat into the wine room no matter how much you insulate the walls.
One thing I would add, the white joint tape on the forced air duct (at the boot where it turns up into the floor) most certainly contains asbestos. Likely not the end of the world if you end up replacing that one section yourself, but be aware of the issues working around asbestos and difficulties disposing of it etc.
Portland code would require furring out walls with insulation on exterior walls of the basement, but sorta your call if you want to do it to code… I would. I’ve made 3 cellars in PDX, all stayed close to ideal temps but would inch into the mid 60s this time of the year. My current cellar is actively cooled, though more for peace of mind than anything else. I’d default to 2x6 framing for the extra insulation, sealed door, definitely insulate the ceiling, and factor in all the vapor barrier details in the other Gold’s book. If you can swing spray foam insulation, I’d go that route (one regret of my current cellar).
Re spray foam… I have it under my roof on the top floor, and it’s fantastic. But I wonder if it’s overkill in a wine cellar? At the end of the day, insulation just slows down the equalization of temperature. When you’re dealing with heat accumulated over a couple of summer months that will pass through the floor and exterior walls, even R50 may not keep it all out. Gold makes that point – there is a point of diminishing returns with insulation.
I guess if you have 2x4 studs and only that much space, it could make a big difference versus fiberglass.
Spray foam is great if you can afford it. It becomes the vapor barrier and fills things that even the best cut bats and rock wool can’t. It would have been twice the cost of my Roxul + Thermax for only a little more R value – in the end, not worth it for me. My cellar is really small (4x8, 500 bottles or so) so as you can imagine the costs only go up when the room gets bigger.
But like John said, if you’re stuck with 2x4’s that are already there (or have over obstacles like doors and ducts that you can only avoid with thinner walls) then it’s probably the only way to get enough R value.
It’s a fair point John, though what I like about the idea of using foam in a cellar is using closed cell which covers the vapor barrier idea about as well as anything else out there. One stop if you will.
I originally planned to cut polyiso board panels and use them instead of fiberglass in the cavities, but the framing by the former owner wasn’t square and the joists had warped and twisted with time, so the ceiling and wall cavities were of different widths and nothing was perfectly rectilinear. I was going to have my contactor cut the insulation boards, but then discovered I had a list of about 15 different widths. Hence my weird resorting to a combo of fiberglass in the cavities and board over that. (Ever try to find a warped or crooked stud or joist through 2" board? Let’s just say there were a lot of wasted screws.)
One thing about Gold (unless he’s written a new addition) is that he’s not up to date on insulation materials. There are more options available now than when he wrote his book.
AFAIK, Closed cell spray foam is clearly the best in terms of r-value per inch and acting as its own vapor barrier, but it is the most expensive and also requires you to vacate the premises while it cures due to toxicity. Open cell spray foam is cheaper but not a substitute. “Spider” insulation - which is fiberglass but sprayed on - is a nice compromise and is what I went with in my current (actively cooled) cellar. I used fiberglass bats between the studs and polyiso boards over them in the cellar before that, but that eats up space and is unwieldy to install.
Dave is right here. I would definitely look into closed cell foam, Stephan. When I priced it out, if you do your own framing, it wasn’t really that much more expensive than polyiso DIY. And we didn’t have to vacate the house – we just stayed on the upper story for a few hours while we kept the basement windows and doors open. This may depend on the ventilation in your basement, and the ambient temperature. But I think the older foam used to offgas more toxic vapors than newer foam does.
PM me if you want the contact info for the contractor I used, who I would recommend.
I didn’t consider passive cooling, but my collection is largely in or near it’s prime drinking windows, so I want to keep the temp well under 60 to keep aging effects moving slowly – and my basement is only about 60% under grade.