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Building a root cellar in corner of full basement. No water issues. Humidity is relatively low in winter (SW Montana).

Details: The root cellar will be located inside a full basement . The basement is poured concrete and is heated. The root cellar is going to be placed in a corner where 2 sides will remain bare concrete walls. The two adjoining walls that complete the room are 2x4 construction. It will be cooled by cool air from outside via duct work dropping cold air to bottom of room. There will be a warm air “exhaust” near top allowing warmer air to exit to the outside. I don’t think moisture will be an issue as humidity is typically low even in winter and there is no water in the basement (bathrooms, etc)

For insulation, is it best to use XPS panels or are batts ok?

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    Are root cellars normally insulated? – UnhandledExcepSean Feb 15 at 14:38
  • The point of a root cellar is to keep things cool. Perhaps you've misnamed your space. What's its actual intended purpose? – isherwood Feb 15 at 15:08
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    Serious? If you install a root cellar in a basement that is normally heated, of course it requires insulation! – R fasching Feb 15 at 17:27
  • @Rfasching - Serious ! When people ask for additional information in order to give you advise that YOU ASKED FOR You may find it serves you best to provide that info. How are you going to keep the root cellar cool if it lives in a heated space? Insulation alone is not enough. What provides the cool ? Root cellar's are traditionally below ground or covered by earth and stay cool from the earth. IF you provide more detailed information then you will get a better informed answer. en.wikipedia.org/wiki/Root_cellar – Alaska Man Feb 15 at 18:38
  • So, are you wanting to create a room within a room? If so, what are the walls and floors like in the space? – UnhandledExcepSean Feb 16 at 0:39
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I would use plastic foam panels; they won't be damaged so easily as batts and never absorb water. They could be easily moved to prevent freezing in winter and expose cool soil in summer.

  • The root cellar will be located inside a full basement . The basement is poured concrete and is heated. The root cellar is going to be placed in a corner where 2 sides will remain bare concrete walls. The two adjoining walls that complete the room are 2x4 construction. It will be cooled by cool air from outside via duct work dropping cold air to bottom of room. There will be a warm air “exhaust” near top allowing warmer air to exit to the outside. I don’t think moisture will be an issue as humidity is typically low even in winter and there is no water in the basement (bathrooms, etc) – R fasching Feb 16 at 19:15
  • "Never absorb water" isn't quite accurate. Hot tub covers typically have closed-cell foam (EPS) in them and eventually they weigh 200 lbs. :) – isherwood Mar 20 at 20:11
  • Yes, I didn't take the time to explain. Currently I use Styrofoam panels to float on a tropical fish pond to slow heat loss ;I can feel from the weight of absorbed water that some panels are "more closed cell" than others. – blacksmith37 Mar 22 at 15:07
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It sounds like you will be depending on the surrounding ground to cool the room in the summer. Cooling in the winter is easy. I think you're best bet is to vapour barrier the warm side of the interior walls and use pink insulation in the cavity. Tyvek or some other breathable membrane on the root cellar side of the wall will allow it to breathe. I would insulate the ceiling as well in the same fashion. Applying the vapor barrier to the warm side in the typical fashion is obviously not an option. It's acceptable to run it up the joist, along the underside of the floor, down the next joist and back up and repeat. I've built a few cellars of various levels of complexity and control but never in Montana. I have been to Montana and the climate is similar but a little warmer and much drier then mine in Toronto. I don't know if the vapour barrier and tyvek is necessary but if it's used in house construction there then you should use it. Basically with a cellar you want to move the building envelope inward and then use passive heat control methods.

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