Building a ground-level root cellar in New England

Hi Permies!
I'm in the middle of a building a retaining wall behind the house. I'm a bit late to the idea, considering the stage of the project, but I am wanting to put a root cellar in that hill before finishing the retaining wall and regrading the slope above. Then again, the wall is not built, so now is the time if it's going to get done. I'm in Connecticut, zone 6a, with permafrost supposedly at 42", although winters are getting warmer and warmer, and I'm not sure that is accurate anymore.

Would love some feedback from some Permies more experienced in this area than I. Looking for pretty fast feedback as we really need to build that retaining wall soon to avoid the hill sliding down.

It is a SW facing hill, about 8-10' high, but since it is situated right BEHIND a 2 story house, the house essentially shades the "front face" of that hill most of the day. I should mention that there is a small artesian spring in that hill, so going below grade is not really an option. Curtain drains have already been placed (which will be just under/in front of the retaining wall), and will carry that water away. I realize it's not ideal being SW facing, but the structure can be built into the hill on 3 sides, and the top, leaving just the front exposed.

To make a cellar 8' wide by 10' deep, here's what I'm thinking to do:
*excavate 16' wide by 16' deep, and 2' below ground level
*lay 2' x 2 x 6' thick concrete blocks such that they create an interior rectangle 8' wide x 10' deep as a base, with the front of the rectangle, roughly lined up with what will be the front of the retaining wall (allowing a prettier "face" to be put on the blocks)
*curtain drain will be placed around the foundation, to tie in to the existing curtain drain that runs along with the front of the cellar/retaining wall
*cut the blocks for alternate laying of the next layer, leaving a 3' space for door in front
*again, but blocks for alternate laying of the next layer, and again, so as to make 6' high interior walls of the blocks
*to gain another foot of height, and create a top "shelf", 2, 6" blocks will be laid atop those, lined up with the outer edge of the concrete blocks
*fill the base layer with about 2' of pea stone, to keep it level with the exterior grade
*the top is to be reinforced concrete slab, that will run end to end
*the entire exterior would be treated with sealer, waterproofing, waffle board, etc so as to lead any moisture from the hill, down to the perimeter drain, and those would tie in to the curtain drains, as above
*the slab roof will be flat and covered with sod
*ventilation will be put in, through the bottom half of front door (I expect some contraption that can be inserted to close off cold in winter months), with an exit "chimney" out the back side, near the top and up above the sod
*the front would be faced with wood, but sandwiching in a 2" insulating foam board between the block and the wood face
*the door would be wood-faced, with a 2" foam, backed with plywood
*I will likely run an outdoor extension cord the short distance from the house to have the ability to have a single pull chain light for convenience when inside, and the potential to run a fan for air circulation.

Is this plan solid? Please poke whatever holes you see in this, and even better, please lay out your best input/ideas on how to make this work better as a functional root cellar, within the confines of the challenges as indicated.

If it's just not going to work trying to build a root cellar at ground level, please give me a head's up, as this is not an inexpensive endeavor.

And if it can't work in the dead of winter, could it be used to extend food storage from harvest up until the hard freeze to give more time for consuming and/or canning, etc, and then be used as an ice house until Spring? Or maybe, with some clerestory windows added to the top of the front face, could I use it better to grow mushrooms?

If this is hard to "picture", please let me know and I'll sketch it out and try to add the sketches as attachments.

THANKS IN ADVANCE!!

Hi Dana,
Welcome to Permies!

**Just a note, you do not have permafrost in Connecticut, it would just be a normal frost line at 42 inches.

The short version is that I'm not sure that is the best option. I am not a root cellar expert by any means, so take all this with a grain of salt.

The longer version is that, if I am reading it right, you would end up with a well insulated space above ground with ventilation. I'm not sure it would do enough of what you want it to do. The purpose of the root cellar was to use the temps and humidity of the underground earth to store things for longer. I'm not sure your structure would count as underground enough to do this automatically. At which point you would probably have to add cooling and humidity... and at that point, why not just convert a room in your house or maybe look at an extra freezer? Essentially, if you can't do in ground, then don't build a "root cellar" just build cold storage somewhere. You can do mini root cellars using trash cans, coolers, and things like that to store things just a few feet underground during the winter... but probably not during warmer times of the year.

Dana,

If the hill is steep enough and you are already doing some earthwork and you know you have too much shallow water you are not losing much and can gain something.
If the roof of the cellar will be covered with at least 40" of dirt and sides will be embedded in the hill it will definitely be cooler in summer than anything around. So even if it may be not cold enough for traditional cellar it will still be cooler and can be used for longer storage time, cheese making, cold cuts curing and a shelter.
I would make sure that in summer the entrance is in the shade.

Thanks for the feedback, Matt and Cristobal.

I can definitely make use of the space for cheesemaking, sure! That's exciting, as we will be getting a few milking goats in the next year or two. And I could learn about cold curing of meats and use it that way, depending on the learning curve. I like the possibility of having it as an emergency shelter.

I would love to grow mushrooms, but I think that can only work with light, so I think it'd have to be designated as one or the other use, not multi-use. However, thinking back to my time in the French countryside, it seemed that they used a LOT of actual deep, dark, natural caves to grow mushrooms. I don't recall them being lit up, but who knows? Maybe someone on here? hmmm...

I spoke with the guys who laid the front curtain drain. The existing drainage pipe is down about a foot below grade, so once the first layer of 2' tall concrete blocks is laid as a foundation, I can likely fill it a foot deep with gravel (instead of 2'), to get a foot of depth, as long as the curtain drains can still tie in and flow into the front existing drain. It's not much, and that's about as far as I can push it, but it might help.

Can anyone comment on the use of, say 2" insulation over the slab roof, and how that might compare to earth-only roof insulation? In other words, can the use of insulation on the TOP of the slabs, be used to make up for the insulation of the ideal 40-42" of earth cover... ie: say 2" of insulation and 15-20-25" of earth/sod?

Thanks so much! Any other thoughts, ideas, or input are welcome. Trying to decide by weighing the costs/benefits by tonight. 🙏

Dana,

I think that mushrooms don't care about light, but there may be some that do and I may be wrong.
Is it possible that you would "slide" the structure deeper into the hill? It would work if it's steep enough and the top cover would become thicker. Someone else has to express an opinion about thinner cover but with insulation.
Do you know what is your average yearly temperature? What is the slope gradient?

A quick search on my ZIP says this:
"mild and temperate" year-round. Summers tend to be warm with temperatures reaching into the upper 80s on average, while winters are typically quite cold with temperatures dropping into the teens and twenties on average. Rainfall is spread throughout the year with around 40 inches of precipitation on average annually. Snowfall can be expected from late November through March, though most years will only see around 20 inches of snowfall total. Overall, the climate is quite pleasant throughout the year...

gets 40 inches of rain, on average, per year. The US average is 38 inches of rain per year.

averages 46 inches of snow per year. The US average is 28 inches of snow per year. (my comment: this is WAY down over the past several years)

average of 190 sunny days per year. The US average is 205 sunny days.

gets some kind of precipitation, on average, 128 days per year. Precipitation is rain, snow, sleet, or hail that falls to the ground. In order for precipitation to be counted you have to get at least .01 inches on the ground to measure.

Summer High: the July high is around 83 degrees (my comment: there are many days at 90-100 in mid-summer
Winter Low: the January low is 14 (my comment: but cold snaps can be 0)
Rain: averages 53 inches of rain a year
Snow: averages 46 inches of snow a year

I asked about going in deeper. Yes, the door can be recessed 2' or more, (at least the width of the concrete block, with the door attached to the inner side of the block, rather than the outer) with an overhang over the door for shade, and that might give us a bit more earth for the top.

Would a brick surface on the face help or hinder, rather than the proposed wood. either can have insulation between that and the blocks.

💕

Dana Lapointe wrote:I asked about going in deeper. Yes, the door can be recessed 2' or more, (at least the width of the concrete block, with the door attached to the inner side of the block, rather than the outer) with an overhang over the door for shade, and that might give us a bit more earth for the top.

Would a brick surface on the face help or hinder, rather than the proposed wood. either can have insulation between that and the blocks.

Your climate sounds pretty gentle so entire idea should work.
If you can recess then it will surely help.
If you face the front with bricks and put insulation in between, it will be the best. Inside you will have massive blocks to remain cold and you will additionally insulate them on the outside and nicely finish it. I like it. I would not use any wood, except for door.

I hope you will post some images one day for inspiration for other users.

Cristobal, Unfortunately, I think the brick face will be just too costly, at least at this time. If we want to get it done now, I will have to start with a rough-sawn wood face and door. More rustic for sure, but it'd get the job done.

Would this be a deal-breaker in your opinion on the viability of the project?

thanks again. I appreciate your help!

Dana,

Just do the wood and enjoy a new homesteading tool (cellar).
Try to pick something rot resistant, or do Sugi-Ban finish (charred wood, brushed and oiled).
Later you can redo it in bricks if you like.