water pipes underfloor: conflicting advice: help sought.

[saveasteading]

Continuing from a previous post, we are setting pipes and ducts on the original concrete floor, before insulating around and over them , then screeding.

150eps under 150mm pir.

 

For the kitchen island sink,  we need a hot and a cold feed.

In my opinion they both need insulation to avoid heat loss/ transfer, especially from one to the other.

However, the general builder who is putting in the pipes says that we should have both pipes inside  a single duct and to use barrier pipe which is self-insulating.

I've checked and see that barrier pipe is for contaminated ground, not for insulating (although some non-expert sites say it is insulating).

 

The plumbing contractor  now says the same!

 

Both these guys are trusted and very good at what they are good at.

 

In my opinion they have fallen for the hype from the plasterboard companies and then superfoil, that a layer of aluminium is insulating.

 

I assume that a pipe with an insulating layer (armaflex etc) is tricky/impossible  to get through  a duct.

 

I don't want 2 taps, labelled 'slightly cold' and 'slightly warm'.

 

Your  guidance  please.

 

 

 

 

 

 

[SimonD]

I'm guessing the proposal is to lay all the water pipes in ducts? As Water Regulations does state that no fittings should be embedded in a floor or wall, but people do. I don't know what they're talking about regarding barrier pipe unless they're referring the plastic pipe that has an oxygen barrier as I see no need for the barrier pipe you're referring to - it's confusing. You can, however get pre insulated MLCP which is going to be easier to thread through the ducting, just do it before you introduce bends to make installation easier.

[-rick-]

I think what they are getting at is that plastic pipes have some minimal insulative value compared to copper pipes. Nick was talking in another thread how condensation doesn't tend to form on uninsulated plastic pipes. But that by no means they are insulated.

 

If you are putting these pipes on an uninsulated ground bearing slab then putting some decent insulation on them seems very sensible to me.

 

Someone here warned me off the pre-insulated MLCP pipes as the insulation isn't very thick. So fine for some uses but not if you want a lot of insulation.

[SimonD]

12 minutes ago, -rick- said:

Someone here warned me off the pre-insulated MLCP pipes as the insulation isn't very thick. So fine for some uses but not if you want a lot of insulation.

 

It's fine for this kind of use as it's only to reduce heat transfer between pipes and not to insulate the pipes from external conditions. The MLCP insulation is usually 13mm which is in line with indoor pipe insulation. My assumption is the pipe in the OP will be well surrounded by the insulation being installed around them though?

 

 

[-rick-]

2 minutes ago, SimonD said:

It's fine for this kind of use as it's only to reduce heat transfer between pipes and not to insulate the pipes from external conditions. The MLCP insulation is usually 13mm which is in line with indoor pipe insulation. My assumption is the pipe in the OP will be well surrounded by the insulation being installed around them though?

 

My reading was lots of insulation on top of the duct, none below. I assume there would be free air in the duct also.

 

Edit: and the MLCP stuff I was looking at was 7mm insulation. Not sure I saw any when I was looking with 13mm. Link please?

Edited 21 hours ago by -rick-

[SimonD]

2 minutes ago, -rick- said:

 

My reading was lots of insulation on top of the duct, none below. I assume there would be free air in the duct also.

 

Edit: and the MLCP stuff I was looking at was 7mm insulation. Not sure I saw any when I was looking with 13mm. Link please?

 

Ah, yes, if no insulation below, then it's a problem. Oh, you do test me 😉 https://www.bes.co.uk/riifo-multilayer-pre-insulated-fire-rated-pipe-coil-16-x-2mm-x-100m-blue-27351/

[-rick-]

3 minutes ago, SimonD said:

Oh, you do test me 😉 https://www.bes.co.uk/riifo-multilayer-pre-insulated-fire-rated-pipe-coil-16-x-2mm-x-100m-blue-27351/

 

 and I'm not stopping... This is stuff you have actucally bought and checked is 13mm? I ask, because the photo shows a pipe with insulation that looks thinner than the inner diameter of the tube. 16mm tube, 12mm inner diameter.

 

Edit: Basically the photo looks identical to the ones advertising pipes with 7mm

Edited 21 hours ago by -rick-

[saveasteading]

2 minutes ago, -rick- said:

lots of insulation on top of the duct, none below. I assume there would be free air in the duct also.

That's correct.  

I hadn't thought about condensation within the duct.  It would be a closed environment and not get wetter, but maybe it should be inset within the insulation.

 

the hot feed would be at about 40 degrees, and the cold say 16?? so that's quite a difference. The duct would warm up to a fairly steady 25C or so.

 

I was thinking we might just bond the duct to the lab with expanding foam.  or maybe put 25mm eps under.   But the pipes themselves? mdpe will be better than copper.

[-rick-]

1 hour ago, saveasteading said:

Continuing from a previous post, we are setting pipes and ducts on the original concrete floor, before insulating around and over them , then screeding.

150eps under 150mm pir.

 

Any thought given to putting in a continuous layer of the 150mm eps then putting the pipe with PIR insulation around/40mm? on top (foamed in)

[SimonD]

2 minutes ago, -rick- said:

 

 and I'm not stopping... This is stuff you have actucally bought and checked is 13mm? I ask, because the photo shows a pipe with insulation that looks thinner than the inner diameter of the tube. 16mm tube, 12mm inner diameter.

 

Edit: Basically the photo looks identical to the ones advertising pipes with 7mm

 Okay, here's another link - 9 13 or 26mm insulation https://www.maincor.co.uk/pipe-systems/products/

 

or this: https://wavin.com/gb/p/f38c1cf7-cf05-4844-9e65-3529628340c8/tigris-pexcalpe-pins13bl-25x25-l25?systemId=C05_F001_S278

 

All manufacturers I will use from time to time.

[saveasteading]

None of the links seems encouraging. They skirt round the subject and don't give any numbers or details.

One of them I can see is for heat pumps. 

 

i guess most people just do whatever, and the water works, so there is no feedback. But this is a chance to strive for perfection.

[SimonD]

12 minutes ago, saveasteading said:

None of the links seems encouraging. They skirt round the subject and don't give any numbers or details.

One of them I can see is for heat pumps. 

 

i guess most people just do whatever, and the water works, so there is no feedback. But this is a chance to strive for perfection.

 

I'm not sure what you mean? MLCP pipe is absolutely suitable for hot & cold supplies and at 13mm insulation thickness it's good enough for your purposes, but if it's exposed to external temperature it needs to be minimum 19mm insulation. Here is a link to maincor's technical brochure about MLCP: https://www.maincor.co.uk/wp-content/uploads/2022/02/Maincor-MLC-Pipe.pdf

 

You can then also buy the pipes that are designed to be buried and are preinsulated and ducted as complete units, either with one pipe or 2. Here is maincor's sheet on that kind of pipe.

 

https://www.maincor.co.uk/wp-content/uploads/2025/09/Maincor_AUSTROFLEX_2025_web.pdf

 

The issue is that with water regulations you shouldn't really embedd the pipes unless you absolutely have to. So use some ducting and thread MLCP pipe through the ducting to the outlets. This is high quality stuff.

[Nickfromwales]

17 hours ago, saveasteading said:

None of the links seems encouraging. They skirt round the subject and don't give any numbers or details.

One of them I can see is for heat pumps. 

 

i guess most people just do whatever, and the water works, so there is no feedback. But this is a chance to strive for perfection.

Why are you ducting these? Just lay the 2 pipes in the lower layer of insulation, cutting notches out that allow for the pipes to be wrapped in 9mm wall insulation, and simplify!

 

Your reputable installers are talking out of their b'ttoms. The hot feed will warm the cold feed, so when you open the cold tap it'll go tepid cold > warm > then properly cold again. Defo cannot and should not be able to interfere with each other; basic uk regs say the hot should always run over the top of the cold when clipping feeds around a property, so rising residual heat cannot affect the cold feeds, basic good practice for as far back as I can remember.

 

These pipes have appx ZERO insulative qualities. Bonkers statement.

 

No need for barrier / additional expense.

[saveasteading]

3 hours ago, Nickfromwales said:

These pipes have appx ZERO insulative qualities

I was hoping you might respond.

That's pretty well what I had in mind so, by default, is correct!

 

I will draw a proposal and send it to our m & e guy, to ask if there are any problems with it, and will he supply the pipes or otherwise tell us what to embed.

As I see it, we lay the 150mm eps, then lay the pipes on top, parallel and about 100mm apart. Whether the pipes will tread into the eps or need  notches, we will see. Then pir on top.

If we had thinner insulation I'd use 2 layers locally.

 

Where the pipes need to emerge we will box around so the pir is no screened and  is exposed for cutting out.... so marking out the runs will be essential.

 

@SimonD your links have been interesting. The product looks good but seems mainly to be for ufh. Where it is aimed at domestic water feeds the thing that bothered me, on reflection,  was the long waffly statements without much backup. It looked as if a keen nee recruit was asked to bulk up the spec pages.

The supplier links ended up at " no longer stocked".

@-rick- I think you said the same.

Thanks all.

But further discussion or disagreement is still welcome.

[-rick-]

My remaining thoughts are that I think I would want a duct, rather than direct bury. I'd want to be able to swap things out if there was a problem.

 

If you are willing to put on top of the 150mm eps, then insulation not so needed. Could run individual pipes in conduit then so you could always pull/replace the pipes (like they do in many european countries). Much lower profile this way too.*

 

I'm sure you've got another duct going in for electric stuff but I would try and put at least one more in for future needs. Probably won't use it but if a future need develops and you haven't got it then you are in a world of pain.

 

* No expert so don't know if there is a flaw in this approach I'm not thinking of.