Planning permission (underground)?

[toasty]

Hi,

before I start, no this isn't a windup!

Running a bit short of space in our garden, not really any room to build another shed and besides I'd like to keep the garden the size it is.

I would like another room to use as a workshop, would I need planning permission to build an underground concrete bunker? I was thinking something about 3m x 3m and about 2.4m high. I appreciate there would be a fair amount of work in digging the hole, but is it feasable?

Obviously I'd have to build it to a high standard so that it was strong enough to hold the soil back and the very top of it would only be a foot under the ground.

So would i need planning permission, or can I dig down as deep as I like?

Anyone else done anything similar?

 

[splinter]

I would hazard a guess and say YESyou would need planning promition.The only similar thing I have been involved in was a garage we constructed for someone under their front garden,aldo a similar type of construction was quite popular during the cold-war and around 1939-1941

 

[noseall]

believe it or not, you may find that theres a clause allowing an underground shelter to be built on your own property.
best to check at the local council though.
funny b*g**rs, those planning folks.

 

[rangersman]

If your garden is that tight I would be more concerned with the party wall act and make sure you don't bother next doors (or your own) foundations

 

[toasty]

Thanks for the responses.

No we aren't actually short of space, I just want to maintain what garden we have left, which is easily 80 sq metres of grass.

I've had more chance to think about it now. I reckon a 3meter cubed excavation should give me approx 8foot cubed room - with a hatch in the top. I'm assuming that with a bit of preliminary calculation I should be looking at about £2k to do the lot.

I was thinking 6inch reinforced walls and floors with a 150mm beam and block roof with 3 inch of concrete on top, probably about 12" below the grass

I'm thinking water penetration will be an issue, but I guess a 6" think concrete wall would be water resistant in itself, plus the outer bracing I'll use when I dig the bl*&dy great hole will be 18mm OSB covered in DPM so should act as a barrier in itself.

I was just thinking of the normal 6" sq mesh for reinforcing the floor and walls (I'll pour the concrete in a mould fabricated between two sheets of 18mm OSB braced on the inside with 2x4"s every couple feet to leave me an 8foot internal cube surrounded by 6" concrete.

 

[JohnD]

Noseall is righter than he thought, a fallout shelter is exempt from planning permission and building regs provided that its depth is no greater than the distance from the nearest building (this is nationwode, npot dependent on Local Authority).

I suspect this was from the days when (1) having even a badly built one was better than waiting for the 4-minute warning before you started to dig (2) not being on record at the town hall would prevent panicky council employees or neighbours from knowing they could fight their way into your shelter to save themselves at your expense.

It is a good idea to have an escape hatch at the opposite end to the usual entrance, in case of emergency e.g. fire.

 

[splinter]

You would get water seepage between the jionts in the concrete,eg between the floor and walland wall and roof ,you would need a water inbetween these and any other "cold" joints in the concrete.The 4"x2" backing timber would need to be at least 400mm centres possibly 300mm centres,You will also need to decide if you are going to have a one sided shutter or two sided shutters?
If you are going to have a2 sided shutter ,which from what you have written,you are .You will need a pair of6"x3" soldiers opposite another pair or RMD"strong backs"at no more than 1000mm centres,bolted together top and bottom .Plus you may need more than one layer of 6" mesh in the walls,maybe two layers or 10mm reforced bars .Planning premission seems to be looming and 2 grand might be a under estimate

 

[splinter]

I know I should not ask this ,but what is the"hatch"in the top for

 

[toasty]

Funny you should mention the hatch, it's watching LOST that has given me the idea in the first place!!!

Seriously though I am really considering it.

-Dan

And if i don't need planning or building regs, what is stopping me? nothing!!

 

[toasty]

oh and thanks for the advice everyone.

will probably start this project once summer is over, the wife will kill me if I trash the garden now, I've only just got it looking presentable.

So how long will I take to dig out the 27 sq meters of soil using a 2 tonne digger then? 1hour, one day, one week, one month or a year!!

Answers on a postcard please!!

 

[noseall]

i should have posted it as a sticky, but if you read my "diyers beware" earlier in this format, just because you don't need planning permission, it doesn't make you exempt from BUILDING CONTROL.
you still need to follow the uk's building codes.

use either a 4 tonne digger or a 4wd j.c.b.

 

[toasty]

I was planning on using a block and beam floor for the roof, then putting mesh on the top and then pouring concrete on top.

The 150mm beams look suitable for a 3m span, but I can't see prices for them anywhere.

Would you think this was the best way to construct the roof, and are these beams expensive? I was kind of thinking they might be around 40-50quid each? using 450x225mm concrete blocks I'd need 7 beams I think

Also I notice the point about the concrete leaking at the joins. I think with a bit of cunning you could pour the walls and floor in one go, obviously there would still be a join at the roof, but would it really leak?

I suppose what I'm asking is is a certain thickness of concrete totally waterproof? and does a join need to have a rubber gasket sandwiched between it, or will the the new and old concrete bond together sufficiently to restrict the flow of water through it.

 

[Static]

You would be better off using a waterproof concrete (ie, sika or caltite) they are more expensive that standard concrete but come with a 10 year guarantee. 6" thick walls are a little on the thin side, you will be looking more at somthing like 10-12" and you would be better off forming the cover slab in the same waterproof concrete as the walls and base.
You should also consider ventilation, electrics, heating etc.

 

[splinter]

You would be better off using a waterproof concrete (ie, sika or caltite) they are more expensive that standard concrete but come with a 10 year guarantee. 6" thick walls are a little on the thin side, you will be looking more at somthing like 10-12" and you would be better off forming the cover slab in the same waterproof concrete as the walls and base.
You should also consider ventilation, electrics, heating etc.

10 yrs is not a very long guarantee for a concrete structure

 

[JohnD]

A slight fall on the floor, to a sump, is a good idea for an underground structure, just in case of any seepage so you can pump it out. There is a special kind of concrete flooring tile with a drainage channel under it whose name I forget.


(But I know this is just a fantasy, really