Underground garage cost?
Discussion
We're rebuilding a house on land where a bungalow currently sits. Due to lack of space (width of plot) the garage is proving difficult to accommodate and our architect is trying to steer us toward an internal garage. However, given there's considerable room in the front garden for a long driveway/ramp, I wondered if the PH collective knows how much more an underground garage would cost (per square meter) over an integral garage? Soil type is clay, house will be on a gentle slope which would reduce angle of ramp, all structures above planned garage location will be new too.
I did a barn conversion approx 8 years ago and dug a 8m x 8m basement beneath part of it.
It added an extra £20k to the ground work package, over and above what had already been quoted for normal 1m deep footings. We were lucky in that all removed soil was disposed of on site, if we'd have had to transport it away the cost would have been much much higher (prohibitively so).
If you go for it i'd advise an internal waterproofing system with a sump and pump. Relying solely on an external tanking system is very brave - if it fails your really in trouble.
My only regret was only digging a basement under half the barn, if i did it again i'd do it under the whole thing.
It added an extra £20k to the ground work package, over and above what had already been quoted for normal 1m deep footings. We were lucky in that all removed soil was disposed of on site, if we'd have had to transport it away the cost would have been much much higher (prohibitively so).
If you go for it i'd advise an internal waterproofing system with a sump and pump. Relying solely on an external tanking system is very brave - if it fails your really in trouble.
My only regret was only digging a basement under half the barn, if i did it again i'd do it under the whole thing.
Hundreds of variables to consider and unfortunately I only have a copy of 2001 Spons at home. However, for projects such as this it gives an indicative functional unit cost for full height basement car parking in the region of £11.5k - £19k per car. I think that's a little shy but will be able to check when back at work next week. Depending on size I would budget minimum £25k - £30k per space.
As stated above though, no point in doing half a job if you're going to the trouble in the first place.
As stated above though, no point in doing half a job if you're going to the trouble in the first place.
100 IAN said:
I did a barn conversion approx 8 years ago and dug a 8m x 8m basement beneath part of it.
It added an extra £20k to the ground work package, over and above what had already been quoted for normal 1m deep footings. We were lucky in that all removed soil was disposed of on site, if we'd have had to transport it away the cost would have been much much higher (prohibitively so).
If you go for it i'd advise an internal waterproofing system with a sump and pump. Relying solely on an external tanking system is very brave - if it fails your really in trouble.
My only regret was only digging a basement under half the barn, if i did it again i'd do it under the whole thing.
I did a similar thing with our house (new build), had to put the garage under the house due to planning, cost about £25k to do. I also regret not making it bigger!It added an extra £20k to the ground work package, over and above what had already been quoted for normal 1m deep footings. We were lucky in that all removed soil was disposed of on site, if we'd have had to transport it away the cost would have been much much higher (prohibitively so).
If you go for it i'd advise an internal waterproofing system with a sump and pump. Relying solely on an external tanking system is very brave - if it fails your really in trouble.
My only regret was only digging a basement under half the barn, if i did it again i'd do it under the whole thing.
The biggest single cost factor to consider is whether there is sufficient space to 'batter back' the excavation when digging out the basement garage. If there are adjacent boundaries or buildings (imagine a 45deg angle down from the level of adjacent building foundation levels, if these impinge upon your excavation you have an issue) you will need to hold up the excavation sides by some means as you dig out. If there are adjacent buildings will need an engineered solution to make sure nothing moves whilst excavations are open. All of which will be ££s on the total cost.
If you have lots of clear space around the proposed basement (which sounds the case), you can do a simply large muck shift, either battering back to slopes or a stepped excavation. After building your walls and tanking (also massively simpler in this method) you can simply backfill. A small basement using mass dig and reused backfill is achievable for the £30-£40k mentioned. If you have to hold the excavation sides up, depending on method you could be talking +50%, maybe more.
If you have lots of clear space around the proposed basement (which sounds the case), you can do a simply large muck shift, either battering back to slopes or a stepped excavation. After building your walls and tanking (also massively simpler in this method) you can simply backfill. A small basement using mass dig and reused backfill is achievable for the £30-£40k mentioned. If you have to hold the excavation sides up, depending on method you could be talking +50%, maybe more.
100 IAN said:
I did a barn conversion approx 8 years ago and dug a 8m x 8m basement beneath part of it.
It added an extra £20k to the ground work package, over and above what had already been quoted for normal 1m deep footings. We were lucky in that all removed soil was disposed of on site, if we'd have had to transport it away the cost would have been much much higher (prohibitively so).
If you go for it i'd advise an internal waterproofing system with a sump and pump. Relying solely on an external tanking system is very brave - if it fails your really in trouble.
My only regret was only digging a basement under half the barn, if i did it again i'd do it under the whole thing.
When I did mine, one thing that the structural engineer had to check was that the structure on top of the basement was heavy enough. He said that had there been a high water table and too lightweight a structure then the whole house could potentially have 'floated' upwards.It added an extra £20k to the ground work package, over and above what had already been quoted for normal 1m deep footings. We were lucky in that all removed soil was disposed of on site, if we'd have had to transport it away the cost would have been much much higher (prohibitively so).
If you go for it i'd advise an internal waterproofing system with a sump and pump. Relying solely on an external tanking system is very brave - if it fails your really in trouble.
My only regret was only digging a basement under half the barn, if i did it again i'd do it under the whole thing.
Whilst the concept of a house subsiding made sense, up until that point i'd not considered a house 'floating' upwards if too much of it was in the ground. Makes sense once you think it through, but until then no one had drawn my attention to such a possibility.
Depends on the ground conditions but may be worth sheet piling. As mentioned above heave is a problem so the garage floor will have to be stronger than usual. Making the garage the full width of the house will greatly reduce the possibility of differential settlement. Try to use precast stuff where possible.
I looked at this a while back on a property where I simply wasn't going to be able to build a decent garage above ground. Min at least 4 cars size. Access a good, no properties nearby (apart from the house). Was looking like 80-100K.
Didn't make sense property value wise so I gave up on the idea. Fantastic house, great location. Never mind............
Didn't make sense property value wise so I gave up on the idea. Fantastic house, great location. Never mind............
I also considered an underground garage with car-lift for the house I just bought, as a way of creating more garden space. The cost was ludicrous (well into six figures), and the project manager said in most cases where he's been involved with builds where car-lifts were installed that they rarely get used and the cost of maintaining the machinery can also be prohibitively expensive. Needless to say I went for a normal garage instead.
Interesting thread. I'm half looking into this m'self. I've got a chalet bungalow which is set higher than the road. Currently driveway, say 25m long, slopes up to the house and levels out. I was wondering about digging a flat section of drive from the road, which would go to a garage dug out underneath the house. Sort of like this.
Most googling seems to suggest that this'd be prohibitvely expensive.
Did the OP get much further with his idea, or anyone else with experience?
Most googling seems to suggest that this'd be prohibitvely expensive.
Did the OP get much further with his idea, or anyone else with experience?
Thing is if you are staying at that house forever more then its worth doing and the cost (unless not affordable) is neither here not there.
If you need those car spaces and that's the only solution then you need to do it.or buy a bigger house which no doubt the stamp duty alone would have paid for works.
If you need those car spaces and that's the only solution then you need to do it.or buy a bigger house which no doubt the stamp duty alone would have paid for works.
CoolHands said:
why is removing earth so expensive?
If you've got an unrestricted site 'digging out' the earth is not the expensive bit per-se, its the 'disposing' of it,If you're lucky enough to have enough land and can lose it on site then that's a huge benefit, but having it carted away can cost £££'s
When you're trying to work out how many lorry loads you'll need you need to at least double it compared to the size of the hole
eg a double garage size hole 7m x 7m x 3m = 147 m3 but that is with the soil densely compacted. Once its dug out it'll take up probably 300 m3
A quick google tells me that a typical grab lorry will carry 12-15 m3, so 20-25 lorry loads..............hence why 'losing' it on site is such an advantage!
100 IAN said:
A quick google tells me that a typical grab lorry will carry 12-15 m3, so 20-25 lorry loads..............hence why 'losing' it on site is such an advantage!
Is that how it works in reality? It'd take days for the grab lorry to go back and forth doing 25 loads. Doesnt the trade have more efficient ways of disposing of excavated soil?Gassing Station | Homes, Gardens and DIY | Top of Page | What's New | My Stuff