Basement pump system

[Cookie]

We have a basement planned in our build, and it has a toilet/shower room. It also has the drainage system of floor gullies for the waterproofing runoff water. As far as we are concerned, the waterproofing runoff should be directed to the sump pump (double system) which will remove that ground water. The foul water from the toilet/shower room should be directed to a mini sewage pumping station. That was our plan, as people with no actual knowledge of drainage but with a firm grasp on Google. Anyway - both the architect and the structural engineer feel both systems can drain into one pump, which would be the sewage pump. Everything we've researched says this is not best practice. They disagree. I want two separate systems, they say it's not required. Also, they say the sewage pump must be outside the house and so we need a deep manhole covered shaft for the pump to sit at the bottom below basement floor level, in the driveway area, and this must be accessible for someone to access the pump at the bottom. This is quite a shaft they are suggesting! It just feels wrong, and a couple of pump providers I've asked have said it can definitely go inside the plant room in the basement with a sealed fit lid to prevent any possible smell. So I think we should have a sump pump placed in a well in the plant room, with a fitted cover. Also in the plant room a second well for the sewage pump with a fitted cover. Anyone have a thought on this?

[Bitpipe]

I had a contractor suggest similar (sump & pump for both services) but in end I used an alternative waterproofing system (concrete) and don't have any wet services down there aside from plant room.

 

It's your build, so do what feels right but maybe ask building control for their opinion.

 

What's the rational for the membrane, sump & pump waterproofing system? What's your ground water level in relation to the basement depth?

[markc]

Got to agree with the above, as a new build, why go for secondary water management instead of building waterproof in the first pl;ace.

Then the toilet could go through a maceration pump and save a lot of work

[PeterW]

Would also check how much your waterproofing  system is designed to produce and look at your water table as you’re probably talking about tiny amounts. If it is large amounts as it’s a pumped membrane type system, then it should have its own double redundant pump as should any sewage system. 

[Cookie]

57 minutes ago, Bitpipe said:

I had a contractor suggest similar (sump & pump for both services) but in end I used an alternative waterproofing system (concrete) and don't have any wet services down there aside from plant room.

 

It's your build, so do what feels right but maybe ask building control for their opinion.

 

What's the rational for the membrane, sump & pump waterproofing system? What's your ground water level in relation to the basement depth?

Hi - the ground investigation showed groundwater strike at 7.5m and then 'at rest' 6m. The basement is 3m deep. Basement is ICF. We've been told the best waterproofing is waterproof membrane draining to a sump pump. It's a very wet site at times - neighbours have had trouble with heavy rains pooling around the base of their houses as water runs off the hill behind the builds. The concrete within the ICF is not waterproof.

So is your basement simply waterproof concrete and no other system in place?

Thanks for your help!

[Cookie]

45 minutes ago, markc said:

Got to agree with the above, as a new build, why go for secondary water management instead of building waterproof in the first pl;ace.

Then the toilet could go through a maceration pump and save a lot of work

The basement is ICF and the concrete within is not waterproof, we have asked why, and it's not usual for it be waterproof apparently. That sounds ridiculous writing it out. But the membrane/sump arrangement, we've been told, is the way to go. 

[Cookie]

30 minutes ago, PeterW said:

Would also check how much your waterproofing  system is designed to produce and look at your water table as you’re probably talking about tiny amounts. If it is large amounts as it’s a pumped membrane type system, then it should have its own double redundant pump as should any sewage system. 

I don't have the info yet on how much it will produce, but it's apparently the system we should go with on the ICF and it does have a double sump pump for the waterproofing runoff. Water table 'at rest' on the investigation was at 6m and the basement is 3m, but it can be a wet site - other builds have had trouble with water on their plots after heavy rains. We're basically going with the waterproofing as designed by the architect.

[markc]

1 hour ago, Cookie said:

The basement is ICF and the concrete within is not waterproof, we have asked why, and it's not usual for it be waterproof apparently. That sounds ridiculous writing it out. But the membrane/sump arrangement, we've been told, is the way to go. 

The ICF and concrete core will not be waterproof, but i would still be looking at waterproofing the structure before back filling.

[Conor]

1 hour ago, Cookie said:

The basement is ICF and the concrete within is not waterproof, we have asked why, and it's not usual for it be waterproof apparently. That sounds ridiculous writing it out. But the membrane/sump arrangement, we've been told, is the way to go. 

We went for a self adhesive bituminous system that was laid under the slab and then lapped over the footing and stuck to the ICF walls all the way up to ground level. Comes guaranteed. 100mm perforated perimeter drain and back filled to ground level with clean stone and geo-membrane. We didn't do anything else. The best waterproofing is keeping water away from the building. Drainage around and under the slab is essential. You just need somewhere to drain to....

Edited April 28, 2021 by Conor

[Thorfun]

a couple of comments on this thread as I've done a lot of research for our basement that's being dug out as I type....

 

1. sounds like you're only having 1 form of waterproofing and that's Type C (Internal membrane and drainage channels). Although that is possible to adhere to some BS number that I can't remember for a habitable basement you require 2 forms of waterproofing (although I believe @Bitpipe only has a single form so it is obviously doable). We decided against ICF for our basement as we feel that RC is easier to get waterproof as you can use Waterproof concrete and see the pour when the formwork is struck (Type B) and we're also going for an external tanking system (Type A) to get the two forms. When the basement was originally planned it was with Type B and C waterproofing but our groundworks company said that the Type A and B system is perfectly good and they're offering a 25yr warranty so I'm happy. also means we don't have to worry about internal drainage and gain a small amount of internal space (not that the basement is small) without having to have that drainage channel in the walls. having said that, the Type C waterproofing is highly regarded and for ICF it should work nicely.

 

2. our civil engineer also specified a foul water chamber for our basement toilet. this would've had to be 4.5m deep and the cost for just the chamber and pumps was over £5k and then there was installation to consider! after I found that out I asked them to redesign the foul water to make it all gravity fed and the toilet in the basement will have a macerator. a LOT cheaper! and macerators can also be fed by showers so maybe this would be another option for you instead of a deep chamber.

 

one thing you didn't mention is if the basement is open on one side or fully underground as if it's open to one side then you should be able to use gravity as you'd be on a sloping plot.

[Bitpipe]

3 hours ago, Cookie said:

Hi - the ground investigation showed groundwater strike at 7.5m and then 'at rest' 6m. The basement is 3m deep. Basement is ICF. We've been told the best waterproofing is waterproof membrane draining to a sump pump. It's a very wet site at times - neighbours have had trouble with heavy rains pooling around the base of their houses as water runs off the hill behind the builds. The concrete within the ICF is not waterproof.

So is your basement simply waterproof concrete and no other system in place?

Thanks for your help!

 

Similar ground conditions to us. I think you have been badly advised on using membrane, sump & pump, it will likely never see much ground water. It can make sense when you have a high water table, i.e. above the floor level of your basement or if you use a system like casting piles in situ which are hard to make contiguous.

 

BTW I'm not surprised, basement construction (aside from retrofits under existing) is still something of a rarity in UK so very little working knowledge out there amongst architects. Ours was dead against the whole idea - it will be damp and smelly he said. Turns out he'd never worked on a project with one and it was 'what he had heard'. 

 

A wet site / surface pooling is likely due to poor percolation and heavy soils (clay). When you dig a basement, you have a working gap of about 1m around the basement perimeter that you backfill with something free draining like clean stone. At the bottom of that space, next to the edge of the slab, you have a land drain (perforated drainage pipe, wrapped in teram and covered in pea shingle that drains to a soak away below the level of the basement slab. Ours is a ring chamber that's about 6m down. When it rains, water will run down that to the land drain and never touch the basement walls.

 

2 hours ago, Cookie said:

The basement is ICF and the concrete within is not waterproof, we have asked why, and it's not usual for it be waterproof apparently. That sounds ridiculous writing it out. But the membrane/sump arrangement, we've been told, is the way to go. 

 

I think your instincts are correct, it's not that it will not work but it sounds inappropriate based on your conditions. Feels like someone is 'specifying what they know' rather than what is needed. You can use WPC with ICF - you can't see the quality of the end pour but it it's poured and pokered by an experienced crew then there should be no issues.

 

However you may want to add an external membrane for additional peace of mind  - you then have your two systems (A + B). We only used WPC as it was given a 15 year insurance backed warranty from Sika which our warranty company accepted. We cast in situ vs using ICF as that's what the contractor offered.

 

 

2 hours ago, Cookie said:

I don't have the info yet on how much it will produce, but it's apparently the system we should go with on the ICF and it does have a double sump pump for the waterproofing runoff. Water table 'at rest' on the investigation was at 6m and the basement is 3m, but it can be a wet site - other builds have had trouble with water on their plots after heavy rains. We're basically going with the waterproofing as designed by the architect.

 

I would be amazed if a drop ever made it through, you will however have paid for all the expense and will need to maintain two pumps for redundancy plus alarms for power cuts etc.

 

Go talk to a contractor (not a 'basement expert' but an experienced ground-worker who does sub surface structures like parking garages etc) and/or a SE who has similar experience.

 

[Cookie]

41 minutes ago, Bitpipe said:

 

Similar ground conditions to us. I think you have been badly advised on using membrane, sump & pump, it will likely never see much ground water. It can make sense when you have a high water table, i.e. above the floor level of your basement or if you use a system like casting piles in situ which are hard to make contiguous.

 

BTW I'm not surprised, basement construction (aside from retrofits under existing) is still something of a rarity in UK so very little working knowledge out there amongst architects. Ours was dead against the whole idea - it will be damp and smelly he said. Turns out he'd never worked on a project with one and it was 'what he had heard'. 

 

A wet site / surface pooling is likely due to poor percolation and heavy soils (clay). When you dig a basement, you have a working gap of about 1m around the basement perimeter that you backfill with something free draining like clean stone. At the bottom of that space, next to the edge of the slab, you have a land drain (perforated drainage pipe, wrapped in teram and covered in pea shingle that drains to a soak away below the level of the basement slab. Ours is a ring chamber that's about 6m down. When it rains, water will run down that to the land drain and never touch the basement walls.

 

 

I think your instincts are correct, it's not that it will not work but it sounds inappropriate based on your conditions. Feels like someone is 'specifying what they know' rather than what is needed. You can use WPC with ICF - you can't see the quality of the end pour but it it's poured and pokered by an experienced crew then there should be no issues.

 

However you may want to add an external membrane for additional peace of mind  - you then have your two systems (A + B). We only used WPC as it was given a 15 year insurance backed warranty from Sika which our warranty company accepted. We cast in situ vs using ICF as that's what the contractor offered.

 

 

 

I would be amazed if a drop ever made it through, you will however have paid for all the expense and will need to maintain two pumps for redundancy plus alarms for power cuts etc.

 

Go talk to a contractor (not a 'basement expert' but an experienced ground-worker who does sub surface structures like parking garages etc) and/or a SE who has similar experience.

 

Thanks so much for the advice. Yes, I come from Canada where basements are the norm so it's still surprising to me that it's difficult to get a suitable plan in place. Yes, it's all clay soils so surface pooling is a problem. I'll explore through everything suggested here and hopefully we'll get to a sensible solution. Thanks again.

[Bitpipe]

1 minute ago, Cookie said:

Thanks so much for the advice. Yes, I come from Canada where basements are the norm so it's still surprising to me that it's difficult to get a suitable plan in place. Yes, it's all clay soils so surface pooling is a problem. I'll explore through everything suggested here and hopefully we'll get to a sensible solution. Thanks again.

 

I can recommend the SE who I used, ICF specialists, if you're not satisfied with the advice you're getting. 

 

Is the whole dwelling above ground ICF?

 

[Cookie]

4 minutes ago, Bitpipe said:

 

I can recommend the SE who I used, ICF specialists, if you're not satisfied with the advice you're getting. 

 

Is the whole dwelling above ground ICF?

 

The basement is ICF, and a timber frame for the main house above ground. Do you have a website for your ICF specialists? Thank you!

[Bitpipe]

Just now, Cookie said:

The basement is ICF, and a timber frame for the main house above ground. Do you have a website for your ICF specialists? Thank you!

 

This is exactly what we did.

 

The specific practice I used has gone but the lead engineer (Tara) now works here https://www.buildcollective.co.uk/

 

[Cookie]

49 minutes ago, Bitpipe said:

 

This is exactly what we did.

 

The specific practice I used has gone but the lead engineer (Tara) now works here https://www.buildcollective.co.uk/

 

Thanks immensely. This is really helpful!