drainage runs in underfloor insulation?

[Tom]

My (proposed) floor make up is: ground - blinding-DPM/radon-300mm EPS70-200mm concrete- 75mm screed and my builder wants to run the 110mm drainage runs through the EPS layer rather punching through the DPM and running through the ground. Is this acceptable? I guess I'm worried about the loss of insulation in these areas (albeit less than half of the 300mm thickness). He is also saying we need to do the same for the narrower drainage pipes from showers and basins and T in to the 110mm in the insulation layer. Again, is this what's done? Seems to me too many joins with potential leaks somewhere I will be able to do naff all about once the slab in poured. I'm rapidly losing faith in my builder - not least as we have yet to get above floor level and he has already managed to pour one ICF wall in the wrong place. Not a good week this week ?

[Tom]

Bueller?

[saveasteading]

It might work.

The loss of insulation is very small.

My worry would be that this is an experiment.

The pipes would have to be carefully laid to gradients. which could be tricky. On a concrete bed, and probably surround too. Then the upper insulation is sitting on a bed of concrete very locally and there could be differential movement.

 

So no, I think this is  a bad idea.

 

[Tom]

Thanks mate. Is it an experiment? I got the impression from the builder that it would be normal to do. The pipes would be in the insulation, at worst resting on the DPM/oversite and the concrete slab above is suspended rather than ground bearing, so the weight would not be taken by the insulation/pipes.

[saveasteading]

Explain please. If the concrete above is suspended, is it not still sitting on the insulation?

[Temp]

Our small bore drainage (solvent weld) is in the insulation. The 110mm is in the ground. No problems.

Edited September 9, 2021 by Temp

[PeterW]

@TomTrying to work out why you have 200mm concrete then 75mm screed on top ..??

 

Have you got a section drawing to share ..?

[Mr Punter]

The 110mm pipe should be in a trench bedded in shingle.

 

Can you post up some plans as @PeterW suggests?

 

[Tom]

4 hours ago, PeterW said:

@TomTrying to work out why you have 200mm concrete then 75mm screed on top ..??

 

Have you got a section drawing to share ..?

It's' a long story.... well not that long actually. We have a suspended slab over the whole build and in the main living area are having this powerfloated and polished as the finished floor surface. In the rest of the build we have the slab but will be having other floor coverings but it was too much of as ask to get the builders to sort the levels out for different floor finishes, shower tray formers etc, figured it would be just simpler to add a screed.

 

I don't have a section drawing unfortunately!

[Mr Punter]

You will need to be taking the pipework outside the building as soon as you can, but I don't see a big issue with it running in the insulation.  It may be good to wrap it in compressible material so it is properly supported and does not deform.

[Iceverge]

1 hour ago, Tom said:

It's' a long story.... well not that long actually. We have a suspended slab over the whole build and in the main living area are having this powerfloated and polished as the finished floor surface. In the rest of the build we have the slab but will be having other floor coverings but it was too much of as ask to get the builders to sort the levels out for different floor finishes, shower tray formers etc, figured it would be just simpler to add a screed.

 

I don't have a section drawing unfortunately!

 

It sounds like a roundabout way of doing things. How thick are your other floor finishes?

[PeterW]

2 hours ago, Tom said:

powerfloated and polished as the finished floor surface

Never seen anyone powerfloat and polish a sand and cement screed. It doesn’t polish the same way as concrete as far as I am aware. Has this been shown to you ..?

[saveasteading]

16 hours ago, Tom said:

 

I don't have a section drawing unfortunately!

Can you sketch one then please, then attach as a scan or photo, as i am not understanding this. Where is the insulation for one thing.

[Conor]

We've a few short runs in through the screed insulation, but majority are below the slab in the hardcore layer. Make sure you tape the dpm well to the pipes.

 

I'm assuming building control approved your drainage design? 

Edited September 10, 2021 by Conor

[Tom]

Massive thanks for the replies, all is very much appreciated. Sorry for the delay in getting back, bit of a crazy day yesterday.

On 09/09/2021 at 19:24, Iceverge said:

 

It sounds like a roundabout way of doing things. How thick are your other floor finishes?

 

Haven't finalised other floor finishes but some rooms will be tiled, others wood and bedrooms carpets - so 20-30mm I guess. I just figured pouring the slab in these areas to take in to account these differences would be too big an ask - easier to do it with a screed at the end.

On 09/09/2021 at 20:15, PeterW said:

Never seen anyone powerfloat and polish a sand and cement screed. It doesn’t polish the same way as concrete as far as I am aware. Has this been shown to you ..?

 

We're not pwerfloating the screed Peter, we'll be doing this to the slab in the other half of the build.

 

22 hours ago, saveasteading said:

Can you sketch one then please, then attach as a scan or photo, as i am not understanding this. Where is the insulation for one thing.

 

OK, have done the best I can with the children's felt tip pens!

And also a diagram of what I think would be better than everything in the insulation: the 110mm passing through the DPM into the ground. The wastes from showers can T in to the vertical 110mm and travel through the insulation. The toilets can T in above floor level and be boxed in. Does this look reasonable?

 

 

[Tom]

21 hours ago, Conor said:

We've a few short runs in through the screed insulation, but majority are below the slab in the hardcore layer. Make sure you tape the dpm well to the pipes.

 

I'm assuming building control approved your drainage design? 

 

All plans have been passed by BC, but TBH they are light on detail with regards the drainage. I spoke to BC two days ago and they were, typically, fairly non-commital.

[saveasteading]

The sketches are a great help.

I am thinking that we have different understandings of what a suspended floor is.

Your concrete slab appears to be sitting on a bed of polystyrene.

Suspended would normally mean spanning freely from one structural support to another, and so is unlikely to be on top of polystyrene, especially an exact contact.

 

If the slab depends on the insulation for support then,  I would not be happy with cutting lumps out for the drainage.

Your second sketch is more normal and appropriate.

 

I would also question why the builder does not want to put the drains in the ground, which is normal and easy, and proven.

 

What stage is construction at now?

[Tom]

Thanks mate. I was initially confused a bit by the proposed floor make up but it is a suspended floor as you describe above, in that it is supported on the perimeter by blockwork. The slab itself is spec'd to have two layers of A393 rebar mesh in it. It is designed to take internal blockwork walls laid directly on it with no need for extra footings etc underneath. The EPS is the lowest compressive strength available (EPS70) as it will not be taking any of the load from the slab. We went down this route as the ground we are building on is pretty much all made ground and this way we take all of that uncertainty over what is underneath out of the equation. It also means we can add/move blockwork walls with carefree abandon in the future if we were so inclined.

 

2 hours ago, saveasteading said:

What stage is construction at now?

We're just coming up to floor level now and doing the last bit of oversite preparation before putting the blinding and DPM down.

 

One more question, where should I be aiming to bring the shower waste up - how close to our proposed shower location? I'm guessing we will run a shallow fall of pipework from this to the shower trap itself within the screed?

[Iceverge]

Usually in this scenario it's like this

 

 

All waste water pipework is run straight down through the concrete base and then horizontally towards the perimeter of the building to an access junction. 

 

Is the only reason you're planning to put the slab above the insulation, to allow you the bourgeois pleasures of randomly building concrete blocks whenever and where ever your heart desires?!!!

 

 

When our place was built all pipes were taken straight down into the middle of the hardcore layer below the DPC with 110mm waste pipe and then outside to an AJ. They were left well proud of the final level of the floor and cut down later. They used normal 90deg bends, I gather these would have been better.

 

 

They also Tee'd some joints under the floor. In hindsight it would have been more robust to run each drain outside individually. Soil pipe is very cheap. And join them at one of these

 

It would have made it possible to rod every drain properly should they ever get blocked. 

 

Do you have your shower trays/formers picked out?

[Tom]

8 hours ago, Iceverge said:

Is the only reason you're planning to put the slab above the insulation, to allow you the bourgeois pleasures of randomly building concrete blocks whenever and where ever your heart desires?!!!

 

Ha, yes it was top of the design brief... No, the floor was designed like that due to the nature of the ground. I's an agricultural site, made ground etc. As it was, we ended up digging out most of the made ground down to original ground level so could have made everything back up to spec and had a ground bearing slab. Hey ho, you live and learn I guess. Anyway, we are where we are so will be having this mental floor make up.

 

8 hours ago, Iceverge said:

Do you have your shower trays/formers picked out?

 

Not yet. How critical is positioning of the shower waste pipe at this stage though? How much bodging-room do you have to play with if you have a 75mm screed to alter/shutter/hack out? If I'm T-ing in to the 110mm stack with the shower waste as indicated in my diagram above, how can I be certain it won't empty the shower trap/gurgle etc? Are there rules of thumb with regards the design of this? Found this: https://www.marleyplumbinganddrainage.com/support/installation-advice-and-help/design-advice/soil-and-waste-design-advice/ which seems to indicate my proposed design should be OK.

[saveasteading]

If  the made ground  settles, then the insulation will go down with it, and you will have a gap between insulation and floor. If this gets any draught at all through it then you will have lost the insulation effect. I am really surprised that this is being allowed by BC but more importantly, you should reconsider the whole thing for your own heat economy and comfort

.

Perhaps you can tie the ins up to the floor with wires.

 

I'm also a bit confused by the drawing attached by Iceverge. Perhaps this is much simplified by the company producing it, (to sell insulation or pipes?).

There is no mention of stone base, on which there would be blinding. then normally dpm on that before concrete/insulation/screed.

 

Getting pipes through the floor at exactly the right position is tricky. what seems very precise at foundation stages can be annoyingly approximate when you find that a vertical pipe is too close to/too far from a wall. There is a lot to be said for keeping boxouts around the penetrating pipes, and adjusting/infilling later.

 

 

[Tom]

The ground isn't going to settle now, we've built back up and compacted well, there will be no possibility of ventilation under the slab either, so I'm sure it'll be fine. I think that's a good idea re keeping boxouts around the pipes. I think we'll do that when we pour the lab so we have greater scope for adjustment later on.

[Iceverge]

13 hours ago, saveasteading said:

I'm also a bit confused by the drawing attached by Iceverge. Perhaps this is much simplified by the company producing it, (to sell insulation or pipes?).

Yup. 

 

It was just one of the first ones in Googled. Sorry for any confusion. 

 

 

[saveasteading]

19 hours ago, Tom said:

The ground isn't going to settle now,

Up to you, but I suggest you get this cleared formally by the building inspector. 

Even 1mm of settlement (or other movement) and a gap will be created.

Seasonal movement and drying of the ground could also make this happen, and it is then not resolvable.

 

[Tom]

On 13/09/2021 at 11:46, saveasteading said:

Up to you, but I suggest you get this cleared formally by the building inspector. 

Even 1mm of settlement (or other movement) and a gap will be created.

Seasonal movement and drying of the ground could also make this happen, and it is then not resolvable.

 

Thanks mate, it's all been passed by our LABC. The ground has been compacted well. A few mm drop would not be enough for convection currents, esp as it's all sealed, and the air gap might even improve U values!