Building a shed below ground level

[Gibbo84]

Hello,

I'm new to the forum having followed it for many years. I know my first question is slightly odd but I'd appreciate the help having been unable to find it else where.

I'm thinking of building a single skin shed at the bottom of my garden later this year.
To get more space on the inside without having to apply for planning permission I'm thinking of digging down into the ground a few feet to gain more room on the inside.

I've spoken to my local planning office because I could find no information about it on the planning portal. Believe it or not they said that it would be fine based on the grounds you don't need planning permission for a swimming pool.

If, for example, I go one meter below ground and 2.5 meters above my internal wall height would be 3.5 meters. All 4 walls will be 3m long.

My question is, would 10cm concrete blocks with a pier on each wall give me a strong enough structure? The reason I've chosen single skin is to save on building materials and space.

What is the maximum height I could build a single skin outbuilding using 10cm concrete blocks?

(To deal with the obvious issue of damp I intend to tank the structure up to the damp proof course.)

Many thanks,
Ian

 

[munchingB]

i would do some research on retaining walls as i doubt 10cm is going to stop your garden swallowing your shed..especially after a few days heavy downpour.

i think anything over a metre needs to be properly engineered.

 

[Gibbo84]

Yes, a couple of people have suggested building a retaining wall around the base of the shed so there is an air gap around all the walls to prevent damp.

I'm concerned though of the implications of having a trench around my shed that might become a moat after heavy rainfall.

My whole garden is on a slope. My plan was to put something like a french drain around the base of the structure and then direct the water well away from the shed.

What do you think of using thicker blocks below ground level and up to the damp proof course instead of a retaining wall to prevent my shed from being swallowed?

 

[munchingB]

retaining wall is to keep the soil, which weighs many many tons, from knocking your walls in on you.

 

[^woody^]

Build wall in the ground double skin, and then single skin when out the ground. Keeping the inside face flush.

Add your waterproof barrier to the inside face of the outer skin, and connect this to the barrier in the floor slab to prevent damp ingress

 

[OwainDIYer]

This is not a shed. This is a bunker.

It needs to be engineered as otherwise it will flood, collapse, or float.