Root cellar under slab?

[murd]

I've been making plans to have a 24x30 garage. The concrete guys are planning a footer and then a 4" slab. My wife has asked if we could put a root cellar under the slab at the far end of the floor, using a septic tank (for example). My first answer was no way, but now I'm thinking I should get some second opinions. If only to let the idea down easy.

Would it be possible to do something like this? Would it be cost prohibitive? I tried to search some google examples with no luck. Our site is on a bit of a slope and they're planning on a bit of site prep already. We're in an area of low planning interference so that wouldn't be an issue.

Anyone know of this being done?

 

[marak]

Funny to hear you ask as I have something similar under my basement.

There is a 24" x 24" plywood access panel in the 4" concrete slab floor of my basement. Below my basement floor is a 6' x 6' x 6' hand dug hole that would make any mafia member happy. It appears to have been dug to access utilities which were compromised during the 1965 Good Friday earthquake. It was never stabilized afterwards. It still needs to be lined with shoring timber or CMU. I don't want to fill it in because it will make a perfect root cellar. I can enough carrots, green beans, strawberry and blueberry jam to last me year round, and grow enough potatoes and onions to last most of the year. The temperature is stable and well above freezing even when the outside temperature dips below -20F for weeks on end. For me, it is worth developing into a root cellar.

Question is, how much would one want to pay to have such? That is completely dependent on the individual and what function it would serve them. In mine, I will also store earthquake supplies (this is one of many locations on the premises where items are stored, and this location is protected by two shear walls that I built adjacent to the access panel...my degree is in structural engineering).

What all would you use the root cellar for?

 

[mike93lx]

If this is really a storm shelter/panic room, make sure you do the door properly so you can get out if something happens.

Digging a hole for a septic tank shouldn't be hard and they can form a riser around the opening. Shouldn't be a huge deal, assuming it doesn't cause you any permitting/inspection headaches and it can support the weight, which would be questionable.

Total guesses, but a few grand for the tank and placement, couple grand for form work and excavation?

Might be better to consider an underground storm shelter to get something engineered

 

[BombShelter]

It's not going to meet codes down here, the contractor might not install it without an engineers sign off. Underfloor rooms in our garages typically use "Spancrete" Ceilings and these are full size rooms matching the garage footprint but I'm sure you could do a smaller room

I'm pretty sure a septic tank would be considered "confined space" and you'd have to change some things so you don't have a death trap and you'd have to make sure it had the proper load rating if you put it under your slab.

And if you do it make sure you waterproof the heck out of it, personally I'd use bentonite membrane from CETCO, Voltex for under the floor and Swelltite for the vertical walls. Septic Tanks don't care if water is leaking inside of them but you might.

 

[duneslider]

The storm shelters are very common in some areas of the country, from what I have seen they are premanufactured and easy drop ins. I would explore that route. Might be easier to get through the city than trying to use a septic vault.

 

[billconner]

Root cellars are usually not insulated or waterproofed, and often have dirt or gravel floors. I'd just lay a footing for block walls in one corner of garage. Maybe use steel deck for floor over.

 

[murd]

Thanks for the replies all!

@marak - Yours sounds just like what were were thinking of. We were really only thinking of it as a root cellar, our grandparents used to have them and we thought it would be good for our keeping the veggies stocked up.

@BombShelter - I had looked at the spancrete option for a full basement, but that's definitely out of my price range.

The more I think about it, the more it is probably not something I need to go to through the effort for. Just wanted to make sure I wasn't dismissing it too soon.

 

[Armorpoxy]

Agree with above most definitely would need an engineer to sign off on this since someone will be going into the space and there is a concrete roof above it...

 

[isb cornbinder]

Proper ventilation should be on your list of concerns. Persons die from oxygen deprivation in poorly ventilated "root cellars".
Industrial level confined space rules should be applied.

 

[larry_g]

Anything is possible with the $$ to make it happen. One concern that is going to come up is how are you going to keep the carbon monoxide out? As other have said ventilation is necessary but I can see where some bureaucrat may ask the above since your in a garage with automotive exhausts.

lg
no neat sig line

 

[billconner]

It might be simpler to build a root cellar separate from garage project.