Underground garage advice

[BandOfBrothers]

I know what you're thinking, but my house is particularly suited to an underground garage:

- we already have a basement converted to living space (recently retanked and sumped)

- that basement has a cut out in the ground down at the front of the house, down to about 5ft from the basement floor with clearance to around 7ft from the basement floor level with a window in it and therefore a supporting lintel above it, facing the front drive, where we could put a door through into the underground garage under the front drive.

- we have a reasonable sized front drive (7m by 20m), with nothing built on it and nothing likely to get planning to be built on it.

- I want somehwere dry to store and work on my car(s).

- There is good access to the front drive from a road

Potential negatives:

We are semi-detached and have a close neighbour on the other side of us.

There are no other underground garages in our area

The soil is clay



I understand planning won't be required for an underground garage? Does connecting it to living space change that?

My thoughts would be to dig out the front drive (by JCB and muckaway truck) to an area around 5m wide by 12m long by 3m deep.

Put in a layer of concrete into the bottom that hole with concrete with rebar at a right angle under the edge of where the garage will be and sticking up by about 3 feet.

Have a steel box essentially built to measurement off site, transported to site, dropped in by crane and connected to doorway into basement.

Install car lift.

Cover steel box in concrete.

Finish the top as paved/resin driveway.


Can anyone give any idea on how to go about the above properly and any idea as to likely cost?

[Equus]

BandOfBrothers said:

I understand planning won't be required for an underground garage?

Almost certainly incorrect.

And the only way to get a halfway accurate idea of cost is to have a design prepared and priced (either by a QS or by builders).

[alscar]

Absolutely no expert but would have thought the no planning permission requirement is very dependent upon where it actually is on the property ie if separate and away from the house then perhaps not but underneath ?
Being a semi and on clay soil might also change that requirement.
Seeing what an external conventional garage costs I would guess that anything along the lines you mentioned has got x2 written on it and north of £50k but I that’s a wild stab.
Would love to see a build thread if it happens so best of luck.

[BandOfBrothers]

Equus said:

BandOfBrothers said:

I understand planning won't be required for an underground garage?

This is not the case.

And the only way to get a halfway accurate idea of cost is to have a design prepared and priced (either by a QS or by builders).

Thanks Equus, can you elaborate on the planning permission side of things a little as this will need to be the first step if required.

My understanding that an underground structure did not require planning due to the old rules around bomb shelters from WW2. What particular parts of an underground garage trigger the requirement for planning permission - is it the joining up to the living quarters, being at the front of the house, and/or something else?

[BandOfBrothers]

alscar said:

Absolutely no expert but would have thought the no planning permission requirement is very dependent upon where it actually is on the property ie if separate and away from the house then perhaps not but underneath ?
Being a semi and on clay soil might also change that requirement.
Seeing what an external conventional garage costs I would guess that anything along the lines you mentioned has got x2 written on it and north of £50k but I that’s a wild stab.
Would love to see a build thread if it happens so best of luck.

Thanks, I don't expect it to be cheap, or to add the same value as the cost to the house, but we intend to stay here for a while, I'm getting older and have never had a garage to keep my cars in.

I've also looked around and getting a decent garage nearby is likely to cost at least £40k, so realistically I'd be ok with double that.

[Equus]

alscar said:

... if separate and away from the house then perhaps not but underneath?

I'd say the opposite: if there is an existing (lawful) basement/undercroft and literally the only work involved would be to form a door opening in the existing front wall, with the remainder of the work being internal alterations to EXISTING floorspace, then it might be argued to fall under the scope of Permitted Development (for the door) and Section 55(2)(a) of the T&CPA (for the internal alterations to form the garage).

Otherwise, even the excavations mentioned in the OP would be classed as 'engineering works', which fall within the definition of 'development'.

[Equus]

BandOfBrothers said:

Thanks Equus, can you elaborate on the planning permission side of things a little as this will need to be the first step if required.

My understanding that an underground structure did not require planning due to the old rules around bomb shelters from WW2. What particular parts of an underground garage trigger the requirement for planning permission - is it the joining up to the living quarters, being at the front of the house, and/or something else?

Crossed post, but see above.

Note that the paragraph I linked gives exceptions for work done before 1968, or to repair war damage, which answers your question about WW2.

[BandOfBrothers]

Thanks, very clear Equus.

So the next question, do you think planning would be likely to be approved it being a reasonably busy residential road in a suburban commuter city in the South East (I'm trying not to doxx myself!)?

[alscar]

Equus said:

I'd say the opposite: if there is an existing (lawful) basement/undercroft and literally the only work involved would be to form a door opening in the existing front wall, with the remainder of the work being internal alterations to EXISTING floorspace, then it might be argued to fall under the scope of Permitted Development (for the door) and Section 55(2)(a) of the T&CPA (for the internal alterations to form the garage).

Otherwise, even the excavations mentioned in the OP would be classed as 'engineering works', which fall within the definition of 'development'.

I did say I was no expert thinking you would be along to educate anyway

[alscar]

BandOfBrothers said:

Thanks, I don't expect it to be cheap, or to add the same value as the cost to the house, but we intend to stay here for a while, I'm getting older and have never had a garage to keep my cars in.

I've also looked around and getting a decent garage nearby is likely to cost at least £40k, so realistically I'd be ok with double that.

I know people talk of a local ceiling limit to house value but if that doesn’t bother you and as you say are there for a while then that’s probably nothing to worry about.
Getting the required permission as per E’s comments is presumably the major hurdle.

[Equus]

BandOfBrothers said:

So the next question, do you think planning would be likely to be approved it being a reasonably busy residential road in a suburban commuter city in the South East (I'm trying not to doxx myself!)?

From the level of information given, it's impossible to say.

We managed to get Planning Permission a few years ago (against my advice - the whole project was nutstechnically extremely challenging for a whole bunch of other reasons) to demolish one half of a 1950's suburban semi, and rebuild an entirely new semi-detached house with a basement garage that was worthy of, if not a Bond villain, then at least Gru (in fact we referred to the project in-house as 'Gru's lair'), so anything's potentially possible, but it will depend on precise circumstances.

I'd expect key issues to be visual impact and highways safety.

Edited by Equus on Thursday 18th April 16:03

[BandOfBrothers]

Equus said:

From the level of information given, it's impossible to say.

We managed to get Planning Permission a few years ago (against my advice - the whole project was nutstechnically extremely challenging for a whole bunch of other reasons) to demolish one half of a 1950's suburban semi, and rebuild an entirely new semi-detached house with a basement garage that was worthy of, if not a Bond villain, then at least Gru (in fact we referred to the project in-house as 'Gru's lair'), so anything's potentially possible, but it will depend on precise circumstances.

I'd expect key issues to be visual impact and highways safety.

Edited by Equus on Thursday 18th April 16:03

Thanks. My plan would have it almost invisible from the road and I can't see much impact on highways.

[Peanut Gallery]

I would worry about flooding, basements being the lowest point and all that! - I don't fancy doing a Tavarish (the bloke rebuilding the flooded P1)

[chrisga]

Are you this guy?

[BandOfBrothers]

Peanut Gallery said:

I would worry about flooding, basements being the lowest point and all that! - I don't fancy doing a Tavarish (the bloke rebuilding the flooded P1)

The basement is tanked with a sump and a pump, so as long as the work ties into that properly, it shouldn't be an issue.

[Indecision]

chrisga said:

Are you this guy?

Beat me to it! Was going to link that as inspiration/sanity check (delete as per mental state).

[Biglips]

This is our plan for an underground garage under our back garden. Slightly different to your project but some common themes.

Considerations:

Drainage. Note the attenuation tank
Fire hazard planning. Lots of combustible stuff in garages
Services. Need power, water and drainage
Ventilation. A metal box underground will be a nightmare for condensation
Cost. Ours will be circa £150k before contingency

Hope that helps