Internal cavity drain membrane

[Thorfun]

morning all,

 

our architects as principle designers needed to consult with a waterproofing company to design our basement's waterproofing system and weren't happy with just waterproof concrete and external tanking unless it was signed off by them. the waterproofing company came back with the following:

 

 

to be fair I don't really have a problem with the internal system I was just wondering if anyone had any comments, experiences, preferences, advice for this route of basement waterproofing?

[Mr Punter]

It is fairly risk free to do type C.  You lose a small amount of floor space as you have to build a metal stud wall inside the membrane.  If you line it first with OSB you will not have issues fixing things to it.  You need to form a sump and install pumps in it.

 

I would not spend the extra money on waterproof concrete and external tanking if you have internal as well.  Some on here @Bitpipe? have gone without the internal membrane and had it fully guaranteed.

[Conor]

Normally you need two types of tanking to meet the required standards. In my case the concrete core in the ICF and an external tanking membrane. SDG are happy to guarantee it, and I'm happy with it. Does your tanking system wrap right around the building including under the slab? That what ours does - at the critical junction of the ICF to the slab, we've three layers of tanking - the sheets coming up from under the slab, a "fillet" strip along the junction, and finally the wall membrane that laps over the other two. All self adhesive rubber with primer on the concrete.

 

The tanking guy said the best type of tanking system you can possibly get is a proper drainage system under and around the structure so you never need to rely on the primary tanking systems in the first place. That's why I've spent £2k on stones lol

 

Finally, a tanking system is worthless unless somebody is prepared to write a gurantee on a piece of paper and sign it....

[Thorfun]

18 minutes ago, Mr Punter said:

It is fairly risk free to do type C.  You lose a small amount of floor space as you have to build a metal stud wall inside the membrane.  If you line it first with OSB you will not have issues fixing things to it.  You need to form a sump and install pumps in it.

 

I would not spend the extra money on waterproof concrete and external tanking if you have internal as well.  Some on here @Bitpipe? have gone without the internal membrane and had it fully guaranteed.

thanks @Mr Punter. I'm not so worried about the reduction in floor space as the basement is pretty big! the only issue might be the plant room but I'll figure something out. sump and pumps have already been designed and as we have a sunken courtyard I've requested that we use a single pump in the courtyard to deal with the internal drainage and the sunken courtyard drainage as well.

 

I need to have 2 forms of waterproofing and so the second form is a choice between tanking or waterproof concrete. the waterproofing company have designed waterproof concrete as the second form of protection so we'll probably just stick with that until I can compare costs for the waterproof concrete compared to the external tanking.

 

I've read @Bitpipe's many posts on the subject and initially just wanted to copy him but the architects weren't happy with that solution and as they'd be responsible as principle designer and so got the design by the waterproof company. I have said to them though that if/when I speak to the groundworks companies they suggest Type A and Type B and will fully guarantee it then that will be ok for the architects. so we've a long way to go in our journey and things might change!

[Thorfun]

18 minutes ago, Conor said:

Normally you need two types of tanking to meet the required standards. In my case the concrete core in the ICF and an external tanking membrane. SDG are happy to guarantee it, and I'm happy with it. Does your tanking system wrap right around the building including under the slab? That what ours does - at the critical junction of the ICF to the slab, we've three layers of tanking - the sheets coming up from under the slab, a "fillet" strip along the junction, and finally the wall membrane that laps over the other two. All self adhesive rubber with primer on the concrete.

 

The tanking guy said the best type of tanking system you can possibly get is a proper drainage system under and around the structure so you never need to rely on the primary tanking systems in the first place. That's why I've spent £2k on stones lol

 

Finally, a tanking system is worthless unless somebody is prepared to write a gurantee on a piece of paper and sign it....

 

the system designed is internal and so we wouldn't be using Type A (external tanking like yours) at all. we'd have Type B (waterproof concrete) and Type C (internal drainage). 

 

I'm a cynical person and I am concerned that the waterproofing company have suggested this route as there's more 'profit' in it for them but as I'm not an expert in all this and definitely don't want to have water ingress issues in the basement I have to go with what the experts suggest and are willing to sign off and guarantee.

 

this is one area I don't want to skimp on financially but I also don't want to be taken for a ride!

[Mr Punter]

3 minutes ago, Thorfun said:

the architects weren't happy with that solution and as they'd be responsible as principle designer

 

I don't think the CDM role of principal designer would have anything to do with this.

[Thorfun]

Just now, Mr Punter said:

 

I don't think the CDM role of principal designer would have anything to do with this.

that's interesting. he seemed to imply that if there were issues it would come back to them. 

[Thorfun]

1 hour ago, Mr Punter said:

It is fairly risk free to do type C.  You lose a small amount of floor space as you have to build a metal stud wall inside the membrane.  If you line it first with OSB you will not have issues fixing things to it.  You need to form a sump and install pumps in it.

 

I would not spend the extra money on waterproof concrete and external tanking if you have internal as well.  Some on here @Bitpipe? have gone without the internal membrane and had it fully guaranteed.

 

I also think @pocster is using the same type C waterproofing as well iirc. @pocster?

[PeterW]

1 hour ago, Thorfun said:

sump and pumps have already been designed and as we have a sunken courtyard I've requested that we use a single pump in the courtyard to deal with the internal drainage and the sunken courtyard drainage as well.

 Isn’t that a bit dangerous as it means your external sump is linked to your internal sump, so if the external floods then the internal will flood to the same level...??

[Pocster]

16 minutes ago, Thorfun said:

 

I also think @pocster is using the same type C waterproofing as well iirc. @pocster?

Exactly. I have an internal perimeter drain that goes out the building to two pumps . Dimpled membranes on the wall and floor . Philosophy was manage water rather than try and keep it out .

[Pocster]

Here’s where I got my goodies from . It’s not difficult to install ; we know that because I did it . Any questions just ask

 

https://www.permagard.co.uk/?gclid=Cj0KCQjwreT8BRDTARIsAJLI0KIc5FFw5UwTGFSMNyM4yIH8n4oy8AcTd61sEiiGBQqRF35rN4R4UJoaAs5yEALw_wcB

[Thorfun]

30 minutes ago, PeterW said:

 Isn’t that a bit dangerous as it means your external sump is linked to your internal sump, so if the external floods then the internal will flood to the same level...??

interesting, no one has mentioned that as a possibility. I was trying to negate the need for 2 x sumps and pumps and also trying to remove the need to have a pump internally in the basement.

 

I'll speak to them all about it. thanks for pointing out this possibility.

[Thorfun]

27 minutes ago, pocster said:

Here’s where I got my goodies from . It’s not difficult to install ; we know that because I did it . Any questions just ask

 

https://www.permagard.co.uk/?gclid=Cj0KCQjwreT8BRDTARIsAJLI0KIc5FFw5UwTGFSMNyM4yIH8n4oy8AcTd61sEiiGBQqRF35rN4R4UJoaAs5yEALw_wcB

 

thank you for this! I hadn't thought about doing this DIY as it's not something I want to get wrong and I thought the quote for the waterproofing company to do it was 'reasonable'. plus it means that any issues they will have to get it sorted out. sometimes that piece of mind is priceless. but I will definitely keep the link and keep it all in mind if I need to make some potential savings.

[Pocster]

10 minutes ago, Thorfun said:

 

thank you for this! I hadn't thought about doing this DIY as it's not something I want to get wrong and I thought the quote for the waterproofing company to do it was 'reasonable'. plus it means that any issues they will have to get it sorted out. sometimes that piece of mind is priceless. but I will definitely keep the link and keep it all in mind if I need to make some potential savings.

Understand your point entirely .

Although at the start I intended to do pretty much everything I do get companies  out to quote for install . Because they see my project ‘ non standard ‘ they either charge a fortune or say they’ll install and won’t give a warranty !!! ?

It’s not difficult to install . It is a fair bit of work especially on your own .

Peace of mind is a big thing and if the installer takes the ‘risk’ and you can afford it I.e it doesn’t tank your budget - then get them to do it ; one less thing for you to worry/think about .

Edited October 28, 2020 by pocster

[Pocster]

1 hour ago, Thorfun said:

have already been designed and as we have a sunken courtyard I've requested that we use a single pump in the courtyard to deal with the internal drainage and the sunken courtyard drainage as well.

You want at least 2 pumps . At different heights . Battery back up . When I started with just a hole I went through crap pumps at 1 a month . My basement became a swimming pool when a pump failed !

There are expensive pumps just for this . I just got 2 cast iron ( can check the make / model if you wish ) . So if 1 breaks I can simply Chuck another in . I was struggling to justify maybe 2k on a ‘proper’ system when these yet to fail pumps are about £150 each .

[Thorfun]

3 minutes ago, pocster said:

You want at least 2 pumps . At different heights . Battery back up . When I started with just a hole I went through crap pumps at 1 a month . My basement became a swimming pool when a pump failed !

There are expensive pumps just for this . I just got 2 cast iron ( can check the make / model if you wish ) . So if 1 breaks I can simply Chuck another in . I was struggling to justify maybe 2k on a ‘proper’ system when these yet to fail pumps are about £150 each .

 

ok, thanks. you and @PeterW have made me doubt myself so I've gone back to the plans from the waterproofing company and they have designed 2 x pumps, one internally and one externally in the sunken courtyard. I think where I'm getting confused is that the Civil engineers also wanted a pump in the external courtyard and so I requested that the civil engineer's pump and the waterproofing company's pump are amalgamated so we only have the one pump externally. but we still have a double sump pump internally in the plant room. sketch attached below.

 

 

8 minutes ago, pocster said:

Battery back up

isn't that what the Powerwall 2 is for?

[Thorfun]

actually, just checked my email trail and this was written...

 

"With regards to sump pumps we has proposed an internal Delta V3 Dual and an external Delta V3 Single to the sunken garden, it may be possible to revise this to relocate the Delta V3 Dual to the sunken garden and do away with the Delta V3 Single, and this would be dependent on the proposed drainage to and around the property."

 

so the waterproofing company are suggesting it's possible to just have the dual sump pump externally and nothing internally. I'm assuming the dual sump pump will have 2 pumps for redundancy.

[Pocster]

6 minutes ago, Thorfun said:

 

ok, thanks. you and @PeterW have made me doubt myself so I've gone back to the plans from the waterproofing company and they have designed 2 x pumps, one internally and one externally in the sunken courtyard. I think where I'm getting confused is that the Civil engineers also wanted a pump in the external courtyard and so I requested that the civil engineer's pump and the waterproofing company's pump are amalgamated so we only have the one pump externally. but we still have a double sump pump internally in the plant room. sketch attached below.

 

 

isn't that what the Powerwall 2 is for?

Lol ! Pw2 only just gone in ! As my project is taking ‘sometime’ I still needed a ups . I’ll keep the ups anyway . So pumps have ups , which has Tesla pw ?

Incidentally my pumps have a ups each . Can you see I worry about failure and my house flooding ! . I will add z wave plugs to each pump which report wattage used . As pump 1 is higher than pump 2 - I know if pump 1 comes on something bad has happened to pump 2 ! . Bolts ‘n’ braces and then more bolts ???

Edited October 28, 2020 by pocster

[Thorfun]

1 minute ago, pocster said:

Lol ! Pw2 only just gone in ! As my project is taking ‘sometime’ I still needed a ups . I’ll keep the ups anyway . So pumps have ups , which has Tesla pw ?

Incidentally my pumps have a ups each . Can you see I worry about failure and my house flooding ! . I will add z wave plugs to each pump with report wattage used . As pump 1 is higher than pump 2 - I know if pump 1 comes on something bad has happened to pump 2 ! . Bolts ‘n’ braces and then more bolts ???

 

yeah, some form of remote monitoring will definitely be on the cards as well here.

[Pocster]

19 minutes ago, Thorfun said:

 

yeah, some form of remote monitoring will definitely be on the cards as well here.

I good excuse for HA !!! ?

[Pocster]

2 minutes ago, pocster said:

I good excuse for HA !!! ?

Without being rude but I detect your interest is building the house ASAP and living in it . Not a lifetime diy project ?

If you’ve got the funds ( and to build your Tesla gigafarm ) then get ‘professionals’ to do it ....

[Thorfun]

14 minutes ago, pocster said:

Without being rude but I detect your interest is building the house ASAP and living in it . Not a lifetime diy project ?

If you’ve got the funds ( and to build your Tesla gigafarm ) then get ‘professionals’ to do it ....

yeah, you're correct although the timelines to be in are being dictated by SWMBO. if it was me on my own then I could take more time and save more money. 

 

it's a delicate balancing act between time, ability and money!

[Bitpipe]

The big questions are  

 

- where is your ground water level?

- how free draining is your ground?

 

Your ground investigation survey will tell you this.

 

If it's way below the slab level  (ours is >6m, slab is at 3.5m below ground) and free draining ( we are on gravel/chalk) then you're probably good with warrantied waterproof concrete - key is in the warrantied, you need an insurance backed warrantied product from someone like Sika or Krtyen - they will have reps supervise the prep, pour and finish  - all of their product is used (waterbar etc) and they give you a warranty against water ingress for 20 odd years. You should not need anything else. We got an all building warranty (whatever that is ever worth) based on the concrete alone.

 

But if you're investing in membrane,  sump & pump then don't spend on waterproof concrete. But make sure it's warrantied or it's worthless if you have a problem later. Same for external membrane, if the contractor won't stand by (in an insurance backed method, incase they go bust)  any subsequent problems you have are yours.

 

We had friends who essentially built in a small river near the Thames and they got a full warrantied waterproof basement system from Glatthar, but it was very expensive and they had to pay for de-watering during the build - but Glatthar did the whole install and stand by the warranty - it was pre-made WPC slabs with a spray applied external membrane.

 

On 28/10/2020 at 10:36, Conor said:

The tanking guy said the best type of tanking system you can possibly get is a proper drainage system under and around the structure so you never need to rely on the primary tanking systems in the first place. That's why I've spent £2k on stones lol

 

 

Completely agree, we have 1m perimeter of large stone for the backfill (fist sized) and a land drain to soakaway at the bottom.

 

As ever, the most commonly used systems are the go-to default for architects and contractors and given the majority of basements are retrofit in London clay, the internal membrane, sump & pump is the most used system.

 

However if you're casting your basement in a new build it seems defeatist to me to plan a structure that will leak and then catch it inside. Plus you need redundancy on pumps, alarms for powercuts etc. External membranes are only as good as the application and need to avoid damage during backfill.

 

On 28/10/2020 at 10:53, Thorfun said:

I need to have 2 forms of waterproofing and so the second form is a choice between tanking or waterproof concrete. the waterproofing company have designed waterproof concrete as the second form of protection so we'll probably just stick with that until I can compare costs for the waterproof concrete compared to the external tanking.

 

I'd push back against that - find out what insurance backed warranty is being issued on the back of the two systems in parallel? That's the key here. Everyone is always happy to spend your money on what they say you 'need' but make sure its what is actually needed and that you have some comeback if there is a problem later.

 

On 28/10/2020 at 10:53, Thorfun said:

I've read @Bitpipe's many posts on the subject and initially just wanted to copy him but the architects weren't happy with that solution and as they'd be responsible as principle designer and so got the design by the waterproof company.

 

Are the architects backing an insurance policy incase there is a leak? if not then their opinion is nice but not that relevant.

 

On 28/10/2020 at 10:53, Thorfun said:

I have said to them though that if/when I speak to the groundworks companies they suggest Type A and Type B and will fully guarantee it then that will be ok for the architects. so we've a long way to go in our journey and things might change!

 

Again, have you done a full ground investigation and do you know what you're digging into?

[Thorfun]

30 minutes ago, Bitpipe said:

The big questions are  

 

- where is your ground water level?

- how free draining is your ground?

 

Your ground investigation survey will tell you this.

 

If it's way below the slab level  (ours is >6m, slab is at 3.5m below ground) and free draining ( we are on gravel/chalk) then you're probably good with warrantied waterproof concrete - key is in the warrantied, you need an insurance backed warrantied product from someone like Sika or Krtyen - they will have reps supervise the prep, pour and finish  - all of their product is used (waterbar etc) and they give you a warranty against water ingress for 20 odd years. You should not need anything else. We got an all building warranty (whatever that is ever worth) based on the concrete alone.

 

the ground investigation went down to 2m when they hit sandstone. there was no evidence of ground water but the survey was done during the summer. we're on clay which isn't very free draining either.

 

33 minutes ago, Bitpipe said:

But if you're investing in membrane,  sump & pump then don't spend on waterproof concrete. But make sure it's warrantied or it's worthless if you have a problem later. Same for external membrane, if the contractor won't stand by (in an insurance backed method, incase they go bust)  any subsequent problems you have are yours.

 

the internal membrane will be warrantied for 10 years. and it is my understanding from Part C that basements should follow BS 8102 which states 2 forms of waterproofing for habitable spaces, right? so, internal membrane (Type C) and then one of either Type A or Type B.

 

36 minutes ago, Bitpipe said:

However if you're casting your basement in a new build it seems defeatist to me to plan a structure that will leak and then catch it inside. Plus you need redundancy on pumps, alarms for powercuts etc. External membranes are only as good as the application and need to avoid damage during backfill.

 

yes, it does seem a little defeatist but our neighbours have a cellar and they didn't use Type C and then had water ingress so had to add internal waterproofing after it was built. I'd rather not have to go through that if I can get it right from the off. but, as I did say, when I speak to the ground workers I will find out what they think and then take it from there.

 

Also, we need a sump and pump to remove the water from our sunken courtyard and so the internal drains will go to that sump and pump and so there isn't an extra cost involved as we need one anyway.

 

no decision has been set in stone on this yet, even though if I make changes at a later date I will probably need to go back to the structural engineer and civil engineers to amend the plans which will incur an extra cost. I'm not set in my ways, if a better solution can be found then I will take it. I'm happy to admit if I'm wrong.....just not to the mrs.

[Thorfun]

thought I'd add the results from our soakage test just for reference.

 

and the groundwater results

 

 

I will ask the waterproofing company if the architects actually sent this report to them or if they went on a desktop study.