Waterproofing basement

[Pendicle]

@Thorfun we are building a basement open on 2 sides, construction ICF, intended to have UFH in slab only waterproof design has advised us to do in screed, we pushed back and they have given us a design that includes water guard drainage channel which we need to precast in the slab. I think you had the same issue but you went with a screed, is that correct? I saw one of the waterproof drawings and looks like they designed the same channel into the screed. Obviously easier than in the 250mm slab although currently this is what we are looking at doing and trying to get my head around how to actually do it, any pointers!

for reference 

[Pendicle]

This is our design

WYK-SD 039 Stepoc Water and Gas Proofing with Preformed Channel.pdf

[Nickfromwales]

4 minutes ago, Pendicle said:

This is our design

WYK-SD 039 Stepoc Water and Gas Proofing with Preformed Channel.pdf 173.61 kB · 2 downloads

What ICF product / system are you considering atm? 

[Nickfromwales]

And why are you pushing back? Lack of head height? 

[Pendicle]

Hi @Nickfromwales econekt, they are based not far from us and will be an assisted build

[Pendicle]

@NickfromwalesHead height but also I have 250mm of slab that can accommodate UFH, so screed on top seemed a wasted expense but I’m happy to be corrected. It would be easier as you can see from @Thorfun drawing

[Nickfromwales]

5 minutes ago, Pendicle said:

@NickfromwalesHead height but also I have 250mm of slab that can accommodate UFH, so screed on top seemed a wasted expense but I’m happy to be corrected. It would be easier as you can see from @Thorfun drawing

How much insulation have they proposed under the slab?

[Pendicle]

@Nickfromwales our insulated raft is 250mm

 

[Nickfromwales]

4 minutes ago, Pendicle said:

@Nickfromwales our insulated raft is 250mm

 

250mm insulation with 250mm concrete over it? EPS insulation?

 

Then it looks like much thicker ring / intermediate beams too.

 

Just wondering it the SE isn’t exactly enamoured with you cutting a trough in the slab at the perimeter, where the physics are extremely pivotal. 

[Pendicle]

@Nickfromwales SE knows about it but has not said anything although I understand the mesh reinforcement will need to be bent but that did not come from him. He has had the proposed design for over a month and made no comment, shares office with architect who has drawn it up for warrant. We have asked about the bending of mesh and how he proposes this is to be done, still waiting. Maybe you’re right and I need to go for screed disappointed SE didn’t think to say anything before changing drawings, one step forward 2 steps back. Thank you for your comments, I really appreciate them. I will chase SE tomorrow, yet again the shared experience and wisdom on this site has trumped my well paid experts.

[Nickfromwales]

11 minutes ago, Pendicle said:

@Nickfromwales SE knows about it but has not said anything although I understand the mesh reinforcement will need to be bent but that did not come from him. He has had the proposed design for over a month and made know comment, shares office with architect who has drawn it up for warrant. We have asked about the bending of mesh and how he proposes this is to be done, still waiting. Maybe your right and I need to go for screed disappointed SE didn’t think to say anything before changing drawings, one step forward 2 steps back 

Yes, I work on a lot of client projects where disappointment is the norm, from professionals they sought help from (and paid handsomely for the ‘pleasure’).

 

I’m not saying to go for a screed, more just thinking out loud; eg how this can be simplified and therefore become cheaper / faster to do.

 

Bending the pins pre delivery is simple, had this on a project in Oxford, just makes the tying a bit more complicated / time consuming, but plenty ‘doable’.

 

I was more of the opinion that you’d need to be robustly insulated if considering UFH in slab.

 

Has either professional stated this is possible? Some SE’s hate putting pipes in a constructional slab, afaic for zero good reason with a slab this thick! 
 

On the job in oxon I suggested (more demanded) that the upper layer of mesh was dropped to get the requisite concrete cover over the top of the UFH pipes, which they eventually agreed to. 
 

Saved the client thousands in more layers atop, screed, loss of head-height etc.

 

Go rattle some cages (and go from passenger to driver) is my 2 cents.

Edited Sunday at 11:51 by Nickfromwales
Stupid autocorrect ffs

[saveasteading]

I don't really understand what this is about. 

What is a basement "open on 2 sides?

What is the drainage channel for? The wall should not leak if designed properly.

Putting a membrane inside a basement is to resolve an existing leaking basement, not newbuild.

Where does the water go from the channel? Presumably it is 2m or more underground.

[Nickfromwales]

22 minutes ago, saveasteading said:

I don't really understand what this is about. 

What is a basement "open on 2 sides?

What is the drainage channel for? The wall should not leak if designed properly.

Putting a membrane inside a basement is to resolve an existing leaking basement, not newbuild.

Where does the water go from the channel? Presumably it is 2m or more underground.

I was working my way to this being OTT, as essentially we’re just discussing retaining walls for a semi subterranean structure aka a walk out basement.

 

FYI, membranes are very much used in new build basements, haven’t long spec’d a very big 4-sided basement, with a 4m excavation. Measures were needed both inside and out, including internal membrane and 2 perimeter drains, each with their own sumps / pumps due to the size of it.

[Thorfun]

why do you need internal drainage/waterproofing system? we had an external membrane and waterproof concrete. we'd rather keep the water out that deal with it on the inside. @Pocster used the internal system so might have more insight in to what is being proposed for you.

 

with regards to UFH i don't think we've ever really used it in the basement as it's a pretty constant temperature down there most of the time. i would've attached it to the rebar in the slab though if i'd had more time but the second layer of rebar was put on and i couldn't thread the pipes through it and there wasn't enough cover over it to allow us to attach the ufh pipes to the top of the rebar. so we just put it in the screed.

[Conor]

You don't need the internal membranes or drainage. Money for nothing.

 

If it's a partial basement, with perimeter drain and clean stone backfill, then the external membrane and continuous, consolidated concrete are enough. Our partial basement was 200mm ground bearing slab (300mm ring beam) with tanking membrane underneath and on top of compacted type 3 (permeable) stone. So same as your details above but without the internal systems. We've had zero issues in the last four years. We used Koster.

 

We than had 200mm insulation and 50mm screed with UFH on top of the slab. Our SE couldn't get a insulated raft to work as would have needed EPS300 throughout which was cost prohibitive. We've 2300mm head height in the basement.

 

The absolute key thing here is, you've two sides open, which means as long as you've a proper drain, and loads of clean backfill, then the tanking won't reply come in to play.

[Pendicle]

We had the waterproof system designed by a structural waterproofing specialist who was recommended by the ICF company. There are 3 types of waterproofing A, B and C. We need to have 2 types as I understand. Waterproofing outside the basement type A with membrane which also goes under the raft, geotex protection board and drain with backfill of washed gravel ( SE has been asked to guide us on what he wants in backfill)  type B waterproof Concrete does not really work for ICF as you cannot see the end result without cutting away the ICF, our only option was Type C internal drain with membrane. This meets building reg standards in Scotland. The type C will hopefully never be used but it’s a fallback if anything does wrong. I know you could a number of years ago use 2 type As but that is not the case anymore.
@saveasteading we are on a slope the back of the house is basement level and we have created a return on one side with a retaining wall. So a 2 sided basement not a cassette ie 4 sided basement. The internal drain is connected to outside drainage that then goes to pond and soakaway down my sloped garden. That’s the current plan.

@Thorfun yes we have considered not having UFH in basement at all but as the main open wall in basement is north facing and we live in Scotland, thought better to put in during construction rather than regret it later even if we do not have it on all the time. 

@Conor I would agree but I’m being told that I’m required to provide 2 elements of the Type A B and C waterproofing system by building control. 

[Pocster]

14 hours ago, Thorfun said:

why do you need internal drainage/waterproofing system? we had an external membrane and waterproof concrete. we'd rather keep the water out that deal with it on the inside. @Pocster used the internal system so might have more insight in to what is being proposed for you.

I have external land drain around the base . I was told that essentially this will fail over time . My 100% ( !!! ) guarantee of no water ingress is the internal drain set in the screed . Walls / floors all membrane into it ., then out in my case to a sump . The view I was given at the time was manage the water rather than attempt to keep it out . Tbh when the walls weren’t finished I.e can see the membrane I never saw a single drop of water behind it anyway . Overkill better than underkill ?  😊

[Nickfromwales]

14 hours ago, Thorfun said:

why do you need internal drainage/waterproofing system? we had an external membrane and waterproof concrete. we'd rather keep the water out that deal with it on the inside. @Pocster used the internal system so might have more insight in to what is being proposed for you.

It is very dependant on site conditions, ground permeability, water table, hydraulics etc, so no ‘one shoe fits all’ with a true basement for sure   

[saveasteading]

7 hours ago, Pendicle said:

back of the house is basement level 

OK. So you can walk out of the basement  onto this area outdoors. So it is patio rather than basement?

Rain falls into it?

[Conor]

7 hours ago, Pendicle said:

We had the waterproof system designed by a structural waterproofing specialist who was recommended by the ICF company. There are 3 types of waterproofing A, B and C. We need to have 2 types as I understand. Waterproofing outside the basement type A with membrane which also goes under the raft, geotex protection board and drain with backfill of washed gravel ( SE has been asked to guide us on what he wants in backfill)  type B waterproof Concrete does not really work for ICF as you cannot see the end result without cutting away the ICF, our only option was Type C internal drain with membrane. This meets building reg standards in Scotland. The type C will hopefully never be used but it’s a fallback if anything does wrong. I know you could a number of years ago use 2 type As but that is not the case anymore.
@saveasteading we are on a slope the back of the house is basement level and we have created a return on one side with a retaining wall. So a 2 sided basement not a cassette ie 4 sided basement. The internal drain is connected to outside drainage that then goes to pond and soakaway down my sloped garden. That’s the current plan.

@Thorfun yes we have considered not having UFH in basement at all but as the main open wall in basement is north facing and we live in Scotland, thought better to put in during construction rather than regret it later even if we do not have it on all the time. 

@Conor I would agree but I’m being told that I’m required to provide 2 elements of the Type A B and C waterproofing system by building control. 

BC and other parties were happy that the concrete in the ICF constituted adequate type B. I dont think I'd trust it in a full basement with hydrostatic pressure. In a partial basement, the tanking is more like a glorified damp membrane, as you SHOULDN'T get any hydrostatic pressure for any period of time.

[saveasteading]

1 hour ago, Conor said:

SHOULDN'T get any hydrostatic pressure for any period of time.

My thoughts too. If it is open to a hillside then the rain runs off the hill and the water table will be low.

With an external membrane and a carrier pipe at the base, is that all that is required? It's a retaining wall.

Ask a basement waterproofing company for a basement design and you get what is shown, but it isn't a basement unless I'm misunderstanding.