Anybody experience of a subterranean workshop

[porker]

Hi,
Seeing the other threads about workshop builds, I wonder if anyone has experience of a subterranean workshop? I've been in my current house about 18 months now having moved from a place where I built a 9x4.5m block and render workshop so I have experience of that with the planning, build etc.
In my new place I have plenty of land but it is at a higher level than the house. I would need to dig back (into chalk) and excavate about 8-10 feet where I am thinking of constructing around a 7x7m workshop and building a new patio over the roof. The front would be level with my existing driveway. I know the costs will be greater than an above ground workshop but I don't have much of an option. I am happy to tackle the planning side of things, the only complication is that I live in an AONB but there are similar projects around and it would be largely hidden.
My main criteria is water tightness. My current thinking is double or triple concrete block construction with drainage and an external membrane barrier with a concrete panelled roof again with waterproof membrane. I have seen a few sites where people in the US have done them and one in NI but nothing in England.
Any tips would be useful.

 

[Droogs]

There was a couple of underground builds, dig and backfill, on grand designs and I believe the magazine website has various details about them and may have some pointers for you

 

[porker]

Thanks, I'll take a look.

 

[jimmy_s]

I have seen a system used where the tanking membrane was laid inside the outer skin and then built around.

http://www.deltamembranes.com/?gclid=CI ... wwodOUkCdA

It worked very well. I think there is much less chance of a failure in the future with these types of systems compared to external tanking.

Probably not the cheapest way but it seemed to work very well.

 

[Alex_E]

Look at Colin furze underground bunker on YouTube I've stated an underground. Workshop/ garage and I've done the dig out while I had a digger at home and will be building the rest in the new year but I'm stuck between concrete construction or doing it the way Colin has. Again I still need to sort drains and I would tank the inside as well of doing concrete.

 

[AJB Temple]

I had a house about 18 years ago with a detached triple garage and a basement beneath of the same size. When we moved in, it was flooded to a depth of 6 feet. The basement had been built for use as a commercial wine cellar and had a sump and pump that had failed. When it was pumped out, you could see water squirting through the concrete block walls in places with some force. The house was on top of a hill and the ground was clay. I was surprised. The building was covered by an NHBC guarantee and their solution was to install internal tanking to walls and floor, add an additional back up sump and pump, and a dehumidifier vented to outside. After that the room was extremely usable and I would have had no problem using it as a workshop. Things to bear in mind:

You really need to know where your water table is and what the rise and fall of it is to see how much water pressure your tanking system will need to withstand. The structure needs to be built with this in mind.
if the tanking fails, flooding can be quite fast, so a sump pump system is a good thing to have. This is of course dependent on continued power supply.
Make sure that you can insure your machinery and tools.
If you contract the work out, try to get it covered by NHBC or sone other form of valid guarantee: remedial work can be very expensive.
Pay good attention to ventilation - fumes etc accumulate in basements.

 

[AndyT]

My workshop is in the basement of our late Victorian house and it has lots of advantages.
It's part of the house so I don't need to put a coat on and cross a dark garden to get to it.
It's not too cold in winter and pleasantly cool in summer.
Despite having no membranes, pumps or heating it stays dry - wood is stable and tools don't rust. I think this is because it is very well ventilated.

Daylight would be nice but modern fluorescents are very good.

I can't have any big heavy machinery, but I don't really want any.

I do need to make sure that any completed projects are small enough to carry up the stairs, and have just managed this, so far.

So overall, it's just right for what I want.

 

[custard]

You really need to know where your water table is and what the rise and fall of it is to see how much water pressure your tanking system will need to withstand. The structure needs to be built with this in mind.

I'd always be nervous about this with a garage/workshop type structure, it's one thing with a house where the weight of the property is holding it in the ground, but on a smaller structure if the water table rises there are enormous forces trying to float the structure up out of the ground.

Every year impermeable concrete swimming pools get drained, heavy winter rains raise the water table, and then the swimming pool floats up on top of the water, rises up out of the ground, and often then cracks and collapses!

 

[Fatboy]

Look at Colin furze underground bunker on YouTube

Wow, could he be any more irritating? Interesting build but I had to turn the sound down in the end

 

[porker]

Thanks all for your input. Useful stuff.
The Colin Furze video was interesting (although if the post apocalyptic world is full of people as loud as him I probably won't bother!). It looks like for waterproofing he was relying mainly on the waterproof concrete.

I think the water table here is fairly low. Partly because the drive level is level with the intended floor and I have not seen any water ever come through the weep holes in the retaining wall that is there already. I also get my water from a borehole in my neighbours property. They told me when it was bored they had to go down a long way to get to the water table. I am halfway up a hill on chalk so probably pretty good. Having said that this is likely to cost me a lot of money so I am thinking multiple measures if possible.

Thanks for the link to the internal membrane - I actually have part of my house that backs into the same garden and this has this type of stuff and it appears to work. (Unfortunately water still comes in through the roof and the front wall due to a poor job on the patio above. I know it can work though as my brother has a basement tanked with this stuff - when he moved in the basement was completely hidden and he only found it when he lifted a floorboard in his front room! The builder who owned the house had plastered and fitted skirting and steps down there but there was about a foot of water. He tanked it and fitted a floor sump and pump as a backup. Ironically, he has a swimming pool down there now. I discounted the internal solution partly because I want to fix to the walls and I will be able to apply something externally but I think I will take another look.

Good point about a guarantee. I wanted to Project manage myself to keep costs down (I am a Project Manager but not in construction) but am worried about it leaking as I guess it can be expensive to fix after the event.

Hoping to get going in the Spring assuming planning and costs look OK. Will post progress when I get going.

 

[BearTricks]

Frank Howarth on YouTube built his workshop in to the ground so he could have a higher ceiling inside.

Sent from my LG-H815 using Tapatalk

 

[SVB]

A sort of worked example:

https://www.ukworkshop.co.uk/forums...t-06-loads-of-pics-t11826.html?hilit=Workshop

Simon

 

[eoinsgaff]

I've built on the side of a hill and I'm an engineer who spent a long time looking for the best option. I believe that an external membrane all around, including under the slab and finishing 150mm above the finish ground level. A protective hard plastic board then on the membrane and most importantly drainage stone all around the structure from the lowest level possible. This only work when you have heading to run this drain away which I gather you have. Using this method ensures you have no water pressure building up outside the wall.

I think you may have been thinking about this in your first post and it has worked very well for me.

I also think that the most efficient construction method is a reinforced concrete slab and walls built homogeneously to form a RC tank. If your ground conditions are reasonable this would also act as your foundation and outer leaf. Also much easier to apply your waterproof membrane under the concrete slab and up the retaining walls.