Root cellar.

I am thinking of building a root cellar on my farm on the side of my hill.

Can anyone direct me to a good set of plans? Or should I just wing it in the design?

I will be using its walls as support for the walls to an big shed with compost bog, shower and changing room on top at a later date!

It depends what you want to achieve Tom.

Three sides in the hill and wall and door to the front.  Arched roof, turfed,  or flat roof to accommodate the ground floor build on top!

So, only a dug in cellar with structure on top really!

OK. First question. Concrete floor with no DPC, OR...'dirt' floor with stone chippings to walk on?

That's really my big issue!

Right Tom, several problems to begin with, first you have to be aware of the hill as they absorb heat like crazy and you have to overcome this problem with depth, you need sufficient depth to get temperature cool enough and then consistent enough to remove any fluctuations. Generally this would result in going deep enough into the hill and then down.

The floor can be a simple broken hardcore to about 4" (100mm) and tamped down, on top of this you can lay 4" of concrete and insert rebar or any other steel so it protrudes about 2" above the laid concrete, leave it level but with a very coarse finish, and let it harden for a week.

Build the outer walls with concrete blocks and let these dry, then cover the floor and inside of the concrete blocks with a bitumen based waterproofing compound such as that from Toolstation as this is much cheaper than DPC and it lasts for decades if done correctly so cover thoroughly and then apply a second coat to be sure. Lay another 4" layer of concrete for the floor and ensure it binds to the steel reinforcing and is free of air bubbles, this will give you an 8" thick concrete floor which is both waterproof and substantial and do not damage the bitumen layer.

Build your inside walls up several courses and insert brick ties every 4 courses, cut these in half and insert the triangular end into your bricks and leave the free end in your void, once you have several courses you fill the void with a slightly cement rich concrete mixture which is wetted out and the brick ties bind to it, then build more courses of bricks, and be aware of damaging your bitumen coating as you pour the concrete into the void. Repeat this until you are two courses lower then your outer wall and let it dry.

Coat the top of your bricks and poured concrete with a couple of good coats of bitumen and get it thick and bind it into the coating inside your outer wall and let it dry fully.

Cast some roof lintels into T shapes and insert reinforcing steel into them, you also cast an L shaped lintel for each end of the structure and you make these to sit on top of the inner wall and poured concrete. Paint your entire L shaped lintel and first T shaped lintel and put into position, fill the void with the concrete blocks so you have formed a block and beam roof and paint each T shaped lintel with bitumen as you insert it, and coat each section of blocks on top once you set them into the beams.

Backfill the entire outer of the structure nearly to the height of the outer wall and then give the entire roof another coating of bitumen. Pour about 2" of concrete over the entire roof of the structure and you will have a waterproof structure you can build off.

It's amazing but that all made sense to me. Thanks for that.

Just one thing. I thought that a controlled 'dampness' was what is required? Rather than a dry inside! Or does the damp come from the walls?

No you dont, a winter atmosphere is damp enough with the moist air, the walls keep out the ground dampness with their waterproof lining and you only use the damp air.

This is often the problem Tom, you need to control the temperature rather than dampness as cooler temperatures allow damp air to remain damp and not dry out, the other problem is that too much damp rots many crops.

So in fact I am looking for an average lower temp is all?

A lot of the videos I see are from the US, and they have hot summers and cold winters.

Correct Tom, the damp UK climate does the rest as regards moisture and it is very much a case of getting the correct temperature and let a UK nature do the rest.

You have identified your first problem which is a lot of this comes from the US and they have wildly fluctuating temperatures ranging from arid in the summer to well below freezing in winter and they assume a 1 size fits all when in reality, something suitable for Texas wouldn't work in Alaska and vice-versa.