Waterproofing / tanking building

[lotus_esprit_s1]

I have a new build I am building that is partially dug into the hillside (rock / ram), max depth is 1.5m below ground level at one end. The retaining walls are 440mm thick - 4” block on side inside and out, with staggered 4” block bridging the cavity, with 20mm rebar, entire cavity has then been filled with concrete. The architects have spec’d a full complement of Newton waterproofing for the external faces at thousands and thousands of pounds. I mentioned this to the building inspector on his last visit and he remarked that off the record, it was absolutely ludicrous what the architects had specified, he had never seen anything like it for this type of build, it was more akin to a sunken basement in a waterlogged area. He thought I would be wasting my money and recommended painting the external walls with “Blackjack”, and applying overlapped DPM lengthways, and would be more than happy with that, along with 110mm perforated land drains along the wall lower edge.

Can anyone offer any thoughts on this before I go ahead with the building inspectors recommendation?

(I now know the architects / structural engineers have massively over engineered this to a ridiculous level - footings are in solid rock / hard ground, yet were specced at 2m wide, fully reinforced with 16mm rebar caged structure at 300mm centres)

 

[brightspark]

blackjack and and dpm membrane and land drain and pea gravel will work fine ive just tanked someones garage wall the water was pi.ssing in and flooding the floor dug all round and put land drain in and gravel job done there well chuffed when it hisses down no water in sight

 

[Onoff]

You'd do well to get yourself on the buildhub forum.

As an aside this book is excellent. I had it but lent it to a neighbour. Lots in there about tanking such walls and back filling with aggregate to allow drainage.

The Complete Book of the Underground Houses: How to Build a Low Cost Home: Amazon.co.uk: Roy Rob: 9780806907284: Books

Buy The Complete Book of the Underground Houses: How to Build a Low Cost Home by Roy Rob (ISBN: 9780806907284) from Amazon's Book Store. Everyday low prices and free delivery on eligible orders.

www.amazon.co.uk

 

[KaneH]

It’s all about warranties / insurance with waterproofing. Anything below ground is considered basement work (even 100mm) and is treated the same as though you were 5 stories down into the dirt. Absolute madness but it’s the approach the insurers are taking. The detail that the architect has provided will likely have been provided by Newton based on your building layout. Build to Newtons detail and they will offer warranty on the detail as well as the product warranties. Choose to deviate from the suppliers “approved” detail and they won’t offer any warranty on the installed arrangement. So if something starts to leak you’ll end up having to sort it yourself.

The likelihood of a correctly installed membrane system with adequate protection / drainage of failing is very small but as I say it’s a risk that suppliers aren’t willing to take. Similarly, architects insurers won’t take too kindly to a deviation from a suppliers approved detail so the risk is being avoided at a cost to you. Great eh!

 

[sako243]

Two walls of my workshop are similar to you in that they are about 6ft below the neighbours farm yard. When I moved in water was ******* through a hole in the wall when it was damp. Got a digger in, dug a trench down to my internal ground level (couldn't go much deeper for a variety of reasons). Put a 6" land drain coil in there and a couple of access pipes for rodding if needed. Backfilled with 4" drainage stone about 18" wide from the wall. Four years on water floods out through the pipe when it's wet but no water comes through the wall. We didn't go anything, not even repointing the stone below ground to the original wall.

 

[Smallfry]

One side of my workshop is built into a bank at about the same depth also on a raft foundation.
Very aware of damp, I laid a couple of layers of membrane before pouring the slab, carefully shaping, folding, and sealing all the corners and edges, and leaving a large excess to go the wall a couple of feet. Land drain and geotextile at the bottom. As I built up the hollow block wall incorporating rebar, I used blackjack as I went, and used the widest DPC in overlapped layers up the wall, also backfilling with pea shingle as I went. All this sounds complicated, and pictures would help, but I don't have any.
Place is as dry as a bone. I have tools and welded stuff in there that has not been painted, and even that has no rust on it, so it must be working !

 

[Agrismith]

It’s all about warranties / insurance with waterproofing. Anything below ground is considered basement work (even 100mm) and is treated the same as though you were 5 stories down into the dirt. Absolute madness but it’s the approach the insurers are taking. The detail that the architect has provided will likely have been provided by Newton based on your building layout. Build to Newtons detail and they will offer warranty on the detail as well as the product warranties. Choose to deviate from the suppliers “approved” detail and they won’t offer any warranty on the installed arrangement. So if something starts to leak you’ll end up having to sort it yourself.

The likelihood of a correctly installed membrane system with adequate protection / drainage of failing is very small but as I say it’s a risk that suppliers aren’t willing to take. Similarly, architects insurers won’t take too kindly to a deviation from a suppliers approved detail so the risk is being avoided at a cost to you. Great eh!

Unless of course the insurance is through bc and the inspector will sign it of but otherwise yes if the architect design is the insurance approved design it needs to be followed.

 

[Onoff]

Seem to recall from buildhub that a "water bar" is a thing if you're say casting a slab then the walls later for a basement esque structure. If it's not poured in one homogeneous hit of waterproof concrete then the joint is obviously a weak point. A water bar gets installed and swells (with water) to prevent ingress.

 

[Morrisman]

When I lived in the Philippines they would build large water storage tanks out of concrete block, then rendered inside and out with cement, and they add something called Sahara into the cement, and it seemed to work.

Our swimming/paddling pool was done with the same stuff, and it was built half above ground for various reasons. I never saw water leaking out of the pool.

Does anything like this exist in the U.K.?

 

[sako243]

Pudlo I think

 

[gaz1]

tanking and french drain within a property with a water pump

its not the paint on type as its the wrong thing to use with stone soil built walls as the walls need to breathe

https://www.mig-welding.co.uk/forum/threads/tanking-old-houses.102976/