Big Basement with pool

[Raju Singh]

Hi guys

 

Would really appreciate any advice on building a big basement with indoor pool (400sqm, 3m high ceilings, 10m*4m pool)

The swimming pool would have 1m below ground and 50cm above ground level

Early considerations include:

• the plot is a 1.1acre and luckily there are no considerations of neighbouring boundaries etc
• access is good 

 

Ground investigations have been completed for my house, and the house next door, they show the same thing more or less, these can be uploaded as requested

Without going into loads of detail, summary:

• Windlesham formation units: silty glauconitic sand to around 4.5m, then clay
• Encountered water around 2-2.5mbgl in areas (not everywhere)

On the basis of the above 

• shoring recommended, perhaps sheet piling needed (ground collapses around the dig quite fast in areas)
• dewatering needed (it looks like there is perched water around 2-2.5mbgl)

 

We (the groundworks team and my appointed SE) have concluded so far that:

We dig out 1.5mbgl - this area would be stable.  Then dewater and pile below this (keeps piling cost down).

We need to get to around 4.5-5.5mbgl for the basement (to include services etc and headlight approx 3m and 1m for the pool)

 

Main areas of advice please to relate to potential costs of:

1. Potential Piling needed
2. Basement construction

Also any recommendations of contractors around the Windlesham, Surrey area?

 

I have received a quote from Glatharr prefabricated basements at around £500K (10 week build time)

Other traditional builds are running at around £400K-£1mill! (4-6months build time)

Prices include waterproofing and 10 year warranties etc

 

Everyone so far has recommended against ICF, although the nudura rep seems to think its totally possible

 

I think I want to go with the germans - because:

• They are German
• This is specialised work
• Basements leak in our area
• The house on top will only be as good as the basement below etc
• Much quicker build and I want to get on with the rest of the house

 

BUT Is £500K a crazy price?

 

Many thanks in advance for any help/advice 

 

Best

 

Raju

 

 

[Thorfun]

welcome. sounds like an amazing space. there are a few on here that have basements and I'm sure @Bitpipe will add his experience in due course. I've just gotten to watertight stage with our build and we have a basement and, tbh, I don't think £500k is far off the mark for a 400m² basement when digging down 4.5m! we have 3m ceilings and 120m² and, if I subtract what I think the foundations without the basement would've been, I estimate it cost us about £1200 - £1250/m². so £500k seems about right to me although I guess it all depends on what that includes. if it's all internal walls, watertight with 2 forms of waterproofing and all the light wells and dealing with the water etc then I'd say it sounds reasonable. I've heard stories of £1000's a week just on pumps to keep sites dry.

 

good luck and I look forward to following your progress should you choose to post about it! ? 

[Ronan 1]

Did your quotes include for excavation and piling if so I'd say 500k was very cheap.

 

If you going sheetpile route, you will want to lower the ground to withing 3 to 3.5 meters in order to allow the sheets to work in cantilever to avoid any bracing which adds big moneys as not only is there the hire and install but it can affect the excavation sequence along with the construction sequence.

[ToughButterCup]

Welcome. Or should I say Wilkommen?

 

15 minutes ago, Raju Singh said:

...

I think I want to go with the germans - because:

• They are German
• This is specialised work ...

BUT Is £500K a crazy price?

 

As a German, I'd say there's nothing all that special about German companies. The reputation of the product also depends on the quality of the build process. So, I'd say that one important factor  could well be : will German workers do the job (or supervise the job) , or will their their UK counterparts do everything? As you say, this is specialised work.

Have you asked any similar specialist UK companies to quote yet?

 

Glatharr  (Finished cellars company) will have its competitors.  Because its very common indeed to have a cellar in ze Fatherland. Do a bit of digging around for cellar construction companies in Germany.

[Raju Singh]

Wow

 

Many thanks for so many responses so quickly

 

@Thorfun

The £500K quote is for the substructure of the basement including the lightwells and up to DPC only, ready to build the rest of the house

Does not include:

1. Groundworks
2. Piling
3. Dewatering

 

Includes

1. load bearing internal walls
2. 2 forms of waterproofing

Happy to post as we get going, hopefully get the pre-commencement conditions discharged soon and the old house can finally be demolished

 

@Ronan 1

Was hoping 6m sheets will work, 3m in, 3m out

Any idea how much this will cost?

 

@ToughButterCup

Will defo look into other German companies, thanks

I think the Germans do manufacture and send over - I think whoever they have trained here German or Brit or whatever will put it together

The brand does carry weight in the industry from what I've heard

Their rep Andy has been very forthcoming and informative too

[Ronan 1]

17 minutes ago, Raju Singh said:

@Ronan 1

Was hoping 6m sheets will work, 3m in, 3m out

Any idea how much this will cost?

You might struggle with 3 in and 3 out, it'll depends on the calcs on the ground, you may be pushed to 3.5m or 4m in for 3m in cantilever.

Sorry I am too long gone out of the UK to be able to give any idea on the price now, however make sure you look at the time frame and ask for a price to buy the sheets along with hire them as if they are going to be in a while it may work out cheaper and most companies will offer you a buyback price too especially the way steel is at the minute.

Also especially if go the hire route make sure your SE designs your basement walls as un propped so you don't need to wait for transition slab (if you have one) to hit strength before you can backfill your walls.

 

Edited February 27, 2022 by Ronan 1

[Raju Singh]

@Ronan 1

Thank you, will pass that on to the SE

[Thorfun]

42 minutes ago, Raju Singh said:

Wow

 

Many thanks for so many responses so quickly

 

@Thorfun

The £500K quote is for the substructure of the basement including the lightwells and up to DPC only, ready to build the rest of the house

Does not include:

1. Groundworks
2. Piling
3. Dewatering

 

Includes

1. load bearing internal walls
2. 2 forms of waterproofing

ok, then I'd say it is on the expensive side! as those things not included will be quite a hefty chunk of cash.

 

we hired a local groundworks company who did the digging and insulation under the slab and they then subcontracted the basement build to another company who came in and put up the formwork, steel, waterproofing membrane and poured the waterproof concrete. then when they left the groundworkers built the internal walls and put on the block and beam top. it worked out a very cost effective way of doing it. you can view how we did it on our blog:

 

 

48 minutes ago, Raju Singh said:

Happy to post as we get going, hopefully get the pre-commencement conditions discharged soon and the old house can finally be demolished

glad to hear it. and we love photos on here as they speak a 1000 words or so the saying goes.

[Bitpipe]

We built a 120m2 basement in Berkshire clay/gravel/chalk.

 

Ground conditions were good so no de-watering required, was able to just batter back sides of excavation. Went down 3.5m and ffl was about 750mm above that.

 

We looked at Glatthar, friends of ours building in the water near the thames used them, very happy, but they are not cheap. You're paying for pre-cast concrete panels to be shipped from Germany to UK vs pouring them in situ using concrete from a plant a few miles away from you.

 

We just used a local groundworker firm who did sub-surface structures like parking garages etc. They did shuttered concrete with a warrantied SIKA waterproofing system - we did not require external tanking or internal membrane. That whole package - demo & removal of existing, excavation & muck away, casting of basement, backfill and in ground services (fouls, rainwater, water & ducts for gas) came to £120k back in 2016. Glatthar wanted more than that just for the basement itself.

 

A basement is just an underground concrete box at the end of the day, the SE will design it and any number of firms can construct it to the required standard.

 

If you have good access and are not tunnelling under an existing building then that simplifies life. The dewatering will be expensive, as will the piling and shuttering though.

 

 

[Ronan 1]

I'd echo Bitpipe re the need for a expensive precast solution.it may seem a "specialist " job to you but to a formwork company it's a pretty simple job.

 But I'd say if you have to sheetpile the whole lot (which looks North of 100meters) when you step back 1.5m for working room would come in at or above bitpipes total cost

[Thorfun]

@Raju Singh you will also need to consider ventilation requirements for the humidity of the pool. @AliG built a swimming pool in his house (although it was above ground) and, iirc, has lots of knowledge (and had lots of obstacles to overcome) to do with it all.

 

I wonder if it's even more complicated with a pool in the basement?

[SteamyTea]

1 hour ago, Raju Singh said:

will pass that on to the SE

Ask his views on all metal fixings. Swimming pools have chlorine in the water. This can cause a lot if problems.

[Tennentslager]

Not if you have a fresh water pool.

Or a river, loch or other such nearby, goodness they have public swimming pools in my area...just a thought.

[SteamyTea]

1 minute ago, Tennentslager said:

Not if you have a fresh water pool.

Or a river, loch or other such nearby, goodness they have public swimming pools in my area...just a thought.

A public, council controlled, swimming pool is pretty good.

Very good safety record.

 

[Tennentslager]

You've not been to the Gorbals pool 10 years ago at the height of eastern European immigration.

The culture of posing (model style) for pics by Polish/Lithuanian young woman in swimsuits was new to the southsiders of Glasgow.

[Raju Singh]

LOL

Brilliant 

[Raju Singh]

Has anyone considered self building a basement?

ICF?

 

Im just finding it difficult to get a decent quote

Based in Ascot - if anyone knows of a decent formwork company?

[Thorfun]

our local Groundworker dug a big hole and then outsourced the basement build to McGuinness Brothers Construction based in Luton who did a very good job. 

[Trw144]

On 27/03/2022 at 09:43, Raju Singh said:

Has anyone considered self building a basement?

ICF?

 

Im just finding it difficult to get a decent quote

Based in Ascot - if anyone knows of a decent formwork company?

I'm thinking of self building my basement - undecided on ICF or concrete with separate insulation at the moment. 

[Raju Singh]

Its:

1. ICF self build
2. Formwork company to build and pass over

I've settled with ICF for the basement and pool

My SE is getting his head around it with the Nudura rep tomorrow morning

I'm slowly putting a team together:

1. onsite Nudura expert
2. Site foreman
3. 5 labourers

Concrete and steel are £ through the roof at the minute - I can't imagine prices coming down anytime soon

Just like everything else in the world atm, increased prices generate increased revenues that each industry just gets used to

I think I've come to terms with it, it is what it is

 

What I can't come to terms with is the £300k odd extra the formwork companies want on top of what I estimate the ICF self build to cost 

 

We plan on digging the pool out first and keeping this as the overflow area for dewatering

We have perched water in our area, not really a high water table

So simple dewatering,.. sump pump etc

At least I hope it will be