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Discussion Starter #1
We are in the process of building an underground root cellar. We live in Michigan with a frost line of 3ft 6” and as we have reached our 4 ft digging level (as our root cellar instructions say) we found the ground gets soggy. We still need to dig another foot deeper to pour concrete for the footer.
Now the questions are: Can we still build at this level with the soggy ground? If we come up 2” inches the ground is no longer soggy. Can we just build the root cellar a little higher up and still manage good storage conditions? We prefer not to have to put in a sub pump. Are there any other options for keeping water out?
Also with our frost line at 3ft 6inches, will that cause storage problems?
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If you have no other location options, and must have a cellar, you must water proof the floor and walls. I would line the hole with a water proof pond liner, up to ground level. Then build the cellar. Last, bank the walls on the outside with the excess dirt. You won't have a root cellar, you will have a storage cellar. A root cellar has a dirt floor.
 

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The problem of not going below the frostline in soggy ground is that you may get a lot of heaving of your floor & foundation from the freeze/thaw cycles. Even if you have good water proofing, your building essentially becomes a boat floating in the water table..... Consider building less deep, but earth-berming, effectively making it deeper.

Here in WI, our frost line is 66 inches. It makes the the benefits of building a root cellar cost prohibitive when potatoes only cost 50c/lb in the store. I just keep 'em in the garage heated to `~60deg over winter. They do fine that way, but start to sprout late Feb/ early Mar. Not a problem.
 

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Take a post hole digger and dig a four foot deep hole in the center of the floor. You might get lucky, dig through a layer of clay a few feet down, and drain the area.
 

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I'm thinking the same as muleskinner that you might be getting close to a clay layer. The soil looks like sandy loam which typically is pretty good for drainage. In my area of Mi my soil has about 3 ft. of sand and then about an 8 in clay layer then sand again. Easy drilling fence post until I hit that clay layer but once through its all sand again.
 

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Discussion Starter #7
I think we will give your ideas a try. Dig lower with the post hole digger and see what we find. We do have very well draining soil on our property. Super55 -So would you say if we pass another clay layer (we have had clay patches rather than layers. Otherwise a lot of sand) it may dry up, have better drainage and we could put in the footer?
My husband says he wants to put 3.5 feet of dirt on top of the finished cellar to bring the freeze line (3ft 6”) up and prevent freezing in the cellar. I’m concerned whether the roof can handle it. He says he wants to brace the ceiling and put in extra wood support..
 

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Do the math on that dirt. It is going to be amazingly heavy. Then add the weight of the water that it will be saturated with after a heavy rain.
Rule of thumb: 1 cu ft of water saturated soil weighs 20 lb----a 10x10 roof with 3.5 ft of wet soil on top would need to support 7000 lb (!!)
 

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Instead of putting heavy dirt on the roof why not put 4" of foam insulation over the roof and down the sides? That should give the same effect of keeping the frost at bay.
 
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Discussion Starter #11 (Edited)
Fishhead and doc- your comments got me brainstorming this evening. I got this idea to put a gable roof over the cellar roof (kind of like a second roof). The gable roof sits on the ground around and not on the walls of the cellar. Fill the space between the two roofs with insulation and possibly turn the top into a sort of living roof with a much thinner layer of dirt. This way snow cannot weigh down the cellar roof because the weight is on the ground around the outside of the cellar and rain will run off the roof also. Then hopefully the space with insulation under the roof can protect from freeze. Any thoughts?
 

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As long as you build it strong enough it should work. A domed concrete roof would work but I wouldn't know how to safely design one of those.
 
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Rule of thumb: 1 cu ft of water saturated soil weighs 20 lb----a 10x10 roof with 3.5 ft of wet soil on top would need to support 7000 lb (!!)
There's a typo with the math. A cubic foot of water has 7.48 gallons and water weighs 8.33 lbs per gallon. That's 62 lbs. Soil is much heavier than water so it's got to be more than 62 lbs.
 

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I think we will give your ideas a try. Dig lower with the post hole digger and see what we find. We do have very well draining soil on our property. Super55 -So would you say if we pass another clay layer (we have had clay patches rather than layers. Otherwise a lot of sand) it may dry up, have better drainage and we could put in the footer?
My husband says he wants to put 3.5 feet of dirt on top of the finished cellar to bring the freeze line (3ft 6”) up and prevent freezing in the cellar. I’m concerned whether the roof can handle it. He says he wants to brace the ceiling and put in extra wood support..
If the cellar is ten feet wide or less, use 2x8s with a 12 inch center. In a hay barn this type roof will hold thirty tons of hay. Should be plenty strong enough for your roof.
 

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Some types of insulation absorbs water and has little value. Be sure to use closed cell foam insulation or install the insulation so it will stay dry. Keep in mind water will actually move up hill a bit. (Capillary action)
 

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Discussion Starter #16
If the cellar is ten feet wide or less, use 2x8s with a 12 inch center. In a hay barn this type roof will hold thirty tons of hay. Should be plenty strong enough for your roof.
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89804
Our cellar will be 8x12 ft and these photos show how the cellar is to look and a bit of how the roof will be constructed.
We dug deeper and found water pooling at 64 inches. It is a dry summer so water will be higher in spring. I think we will put a french drain to a 5 gallon bucket which can be removed to be emptied (whether that’s a good idea or not remains to be found out). That way we don’t have to run electricity out to it.
 

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View attachment 89803
View attachment 89804 Our cellar will be 8x12 ft and these photos show how the cellar is to look and a bit of how the roof will be constructed.
We dug deeper and found water pooling at 64 inches. It is a dry summer so water will be higher in spring. I think we will put a french drain to a 5 gallon bucket which can be removed to be emptied (whether that’s a good idea or not remains to be found out). That way we don’t have to run electricity out to it.
In the spring that 5-gallon bucket will fill in less than an hour. If you could extend the drainpipe out to a lower elevation so the sump pit drains by gravity, you will likely have a working solution.

BTW, the rule of thumb for soil at field capacity (not saturated) is 100 pounds/cu ft.
 

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I think we will give your ideas a try. Dig lower with the post hole digger and see what we find. We do have very well draining soil on our property. Super55 -So would you say if we pass another clay layer (we have had clay patches rather than layers. Otherwise a lot of sand) it may dry up, have better drainage and we could put in the footer?
My husband says he wants to put 3.5 feet of dirt on top of the finished cellar to bring the freeze line (3ft 6”) up and prevent freezing in the cellar. I’m concerned whether the roof can handle it. He says he wants to brace the ceiling and put in extra wood support..
Yes it's a possibility you just hit a clay layer and if you get through it draining shouldn't be an issue. When you back fill you want to try to get the clay dug out back at the same level you went through and slope it away from the building. Sealing the exterior blocks is also recommended. I would not in any way recommend putting 3' of dirt on top nor do I think its recommended. In my area of NW LP michigan root cellars are everywhere and most only have maybe 12-18 inches of dirt on top of them. You get a lot of residual heat from the soil to keep it temperate and the snowfalls we get do a great job of insulating when it really gets cold. My grandparents had one that only had about 6" of soil on top of it and they were able to keep things from freezing by just running a 60 watt light bulb when it got down into the single digits.
 

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Discussion Starter #19
Yes it's a possibility you just hit a clay layer and if you get through it draining shouldn't be an issue. When you back fill you want to try to get the clay dug out back at the same level you went through and slope it away from the building. Sealing the exterior blocks is also recommended. I would not in any way recommend putting 3' of dirt on top nor do I think its recommended. In my area of NW LP michigan root cellars are everywhere and most only have maybe 12-18 inches of dirt on top of them. You get a lot of residual heat from the soil to keep it temperate and the snowfalls we get do a great job of insulating when it really gets cold. My grandparents had one that only had about 6" of soil on top of it and they were able to keep things from freezing by just running a 60 watt light bulb when it got down into the single digits.
Thank you! That’s some great info! I did hear about that light bulb idea somewhere recently.. I just can’t remember where.
 

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Thank you! That’s some great info! I did hear about that light bulb idea somewhere recently.. I just can’t remember where.
I've heard the same suggestion for well houses. I guess it gives off just enough heat to keep things from freezing. I wouldn't have thought it would help with something as large as a root cellar though.
 
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