Crazy idea... Basement for my shed

[JRJ]

So... This might sound like a crazy idea but I'm really contemplating it.

When I was granted planning permission for the extension, I also included plans to convert the old coal sheds into usable space namely a storage shed and summer house/bar/gym total footprint about 3.6m x 8.5m, now I would need to scrape out and dig new footings anyway but part of me has got the crazy idea of going deeper and adding a mancave underneath.

I've watched a few YouTube videos of various ways to do this Colin Furze/shipping container/block walls etc but they all differ and all run into different problems with no one solution.

I'm thinking I could effectively build a 2 storey shed with one floor underground, french drains around and tanked walls, I doubt anyone has done it on here but may have experience from trade or regular basements on how to solve issues?

 

[dlockers]

Pfft, rookie.

 

[ik9000]

You done any basement work before?

Basements; they're not impossible, it just needs knowledge, experience and being willing to pay good people instead of budget barry bodgit. Get a proper engineering design. Your council may well insist on it as part of the planning application. It's become increasingly common in the London boroughs since Camden, Westminster and RBKC kicked up a fuss and implemented their basement policies a number of others have followed suit.

A couple of things to consider:

0) a lot of councils do not allow basements in gardens (anymore), they have to be under the house and can only extend a limited distance from it. Check before you invest too much in this!
1) building flotation. Seriously, I've seen them pop-up out the ground in a storm! With only a shed/garage over it there's not much weight to hold it down. Where is your ground water, and what happens in the storm events?
2) soil disposal - it can be really expensive to get it taken away, especially if there are any contaminants, and you are obliged to get it tested I'm afraid. Google WAC testing.
3) as a rough rule of thumb it's 3x more expensive to go down than to stay above ground.
4) heave and associated ground movements. Digging out several meters of soil allows the underlying ground to relax and swell. As this happens the walls move in and there is a ripple effect contouring out on plan for further than you might think. It doesn't take much to start affecting buildings and the like even one or two houses away!
5) given the depths proposed, unless you have a country estate you're probably going to fall into the realm of needing party wall awards. Brace yourself for the fees of all the adjoining owners - which you have to pay IIRC!
6) temporary works. If you don't believe me find the youtube of the clown on grand designs who tried to build a basement without any because the wally of a builder said he could do it without (so far as the programme implied) any proper soil investigation, nor temporary shoring and propping. He is digging 3m of vertical cut unstable soil below the water table and surprise surprise it collapse in. Not only in breach of H&S legislation endangering workers as it started to collapse, but also the surrounding buidlings, where (again implied) it seemed there was no party wall award in place. FFS... and they went on TV!
7) waterproofing, as another thread, water always wins. Allow for min 2 forms of waterprooing as BS8102, one a drained cavity.
8) effect on trees, tree root systems etc.

edit. Your two storey shed idea is probably also contrary to planning restrictions too. It definitely wouldn't be allowed around these parts.

 

[JRJ]

You done any basement work before?

Basements; they're not impossible, it just needs knowledge, experience and being willing to pay good people instead of budget barry bodgit. Get a proper engineering design. Your council may well insist on it as part of the planning application. It's become increasingly common in the London boroughs since Camden, Westminster and RBKC kicked up a fuss and implemented their basement policies a number of others have followed suit.

A couple of things to consider:

0) a lot of councils do not allow basements in gardens (anymore), they have to be under the house and can only extend a limited distance from it. Check before you invest too much in this!
1) building flotation. Seriously, I've seen them pop-up out the ground in a storm! With only a shed/garage over it there's not much weight to hold it down. Where is your ground water, and what happens in the storm events?
2) soil disposal - it can be really expensive to get it taken away, especially if there are any contaminants, and you are obliged to get it tested I'm afraid. Google WAC testing.
3) as a rough rule of thumb it's 3x more expensive to go down than to stay above ground.
4) heave and associated ground movements. Digging out several meters of soil allows the underlying ground to relax and swell. As this happens the walls move in and there is a ripple effect contouring out on plan for further than you might think. It doesn't take much to start affecting buildings and the like even one or two houses away!
5) given the depths proposed, unless you have a country estate you're probably going to fall into the realm of needing party wall awards. Brace yourself for the fees of all the adjoining owners - which you have to pay IIRC!
6) temporary works. If you don't believe me find the youtube of the clown on grand designs who tried to build a basement without any because the wally of a builder said he could do it without (so far as the programme implied) any proper soil investigation, nor temporary shoring and propping. He is digging 3m of vertical cut unstable soil below the water table and surprise surprise it collapse in. Not only in breach of H&S legislation endangering workers as it started to collapse, but also the surrounding buidlings, where (again implied) it seemed there was no party wall award in place. FFS... and they went on TV!
7) waterproofing, as another thread, water always wins. Allow for min 2 forms of waterprooing as BS8102, one a drained cavity.
8) effect on trees, tree root systems etc.

edit. Your two storey shed idea is probably also contrary to planning restrictions too. It definitely wouldn't be allowed around these parts.

@ik9000 Thanks for this much appreciated, first port of call will be the building inspector on his next visit the whole idea could be stopped with a quick chat.
Unfortunately for us we've pretty much had to deal with the majority of your suggested hurdles on the build so far, 200+ ton of clay removed offsite, party wall agreements dealing with underpinning a neighbours property, coal reports and conflicts over required footings Lets say my patience has been tested with Covid thrown into the works as well.

 

[Rroff]

I've never seen anything but problems with shipping containers used in these kind of situations - they aren't designed for it, warping, corrosion, damp, etc. seems to be inevitable in the long term, they also don't seem great from temperature regulation point of view.

 

[ik9000]

I've never seen anything but problems with shipping containers used in these kind of situations - they aren't designed for it, warping, corrosion, damp, etc. seems to be inevitable in the long term, they also don't seem great from temperature regulation point of view.

Shipping containers mostly are fabricated from steel 1-3mm thick (and built up in local areas from combinations of those). Now it's weathering steel, but buried in the ground that is "hello corrosion" and there isn't much there to corrode, so I can well believe it won't perform well. The internal dimensions are also quite meagre for living spaces. It's a bit of a nonsense "solution" for a basement IMO.

 

[Rroff]

Shipping containers mostly are fabricated from steel 1-3mm thick (and built up in local areas from combinations of those). Now it's weathering steel, but buried in the ground that is "hello corrosion" and there isn't much there to corrode, so I can well believe it won't perform well. The internal dimensions are also quite meagre for living spaces. It's a bit of a nonsense "solution" for a basement IMO.

Probably part of the problem as well is people tend to buy or acquire well used ones for this application though even the ones on YT where they prepared them first don't seem to last very well.

 

[sovietspybob]

Having a few shipping containers at work for storage and seeing how quickly they rust into nothing just being outside even with being painted a couple of times i really wouldn't fancy their changes being buried in the damp ground. We've got 1 which is 10 years old and starting to leak with quite a few rust bubbles and that's been painted twice i think in 10 years so you'd maybe get 3 or 4 years at best underground i'd have thought before you started having issues.

We are right by the sea so that'll speed up the corrosion process for sure but it's still better than being in the ground i'd wager.

 

[dirtychinchilla]

Pfft, rookie.

I've been watching this too. He is ******* crazy. I can believe the tunnel going from the workshop to the bunker, but from the house?!

I keep thinking, what if he wants to move? You'd see it as an enhancement to the property of course, but is it even legal? I think he acts like his neighbours don't know, but they probably do.

Love it either way!

 

[MassiveJim]

I've been watching this too. He is ******* crazy. I can believe the tunnel going from the workshop to the bunker, but from the house?!

I keep thinking, what if he wants to move? You'd see it as an enhancement to the property of course, but is it even legal? I think he acts like his neighbours don't know, but they probably do.

Love it either way!

he is you tuber with over 10 million followers I think his neighbour knows lol.
I think the reason for him trying to "keep it a secret" is more to do with the mental amount of noise that he doesn't want to inflict on his neighbour if he used a jack hammer for example

 

[m4rmite]

Colin Furze, turning up the internet to 11 since 2007?

 

[Semple]

Pfft, rookie.

I wonder how he's waterproofed/tanked it. He's only shown the construction of putting up steel reinforcement frame, followed by an inner frame and filled the void with concrete. I'm sure if there was a flood then it would seep it no problem.

 

[m4rmite]

I wonder how he's waterproofed/tanked it. He's only shown the construction of putting up steel reinforcement frame, followed by an inner frame and filled the void with concrete. I'm sure if there was a flood then it would seep it no problem.

He seem welded the steel sheets.

 

[ik9000]

He seem welded the steel sheets.

Can work but it can take a few visits to get right. I've seen a lot of sheet pile walls leak where the clutch welds have missed a spot, blown out etc. Best seen as a way to slow ingress than a complete solution by itself. Coupled with some tanking and water resistant concrete you could start getting somewhere.