Alternative floor build-up for UFH

[Ben Weston]

Hi all,

 

We're looking to have 5G click LVT flooring throughout downstairs. We have wet underfloor and I realise the traditional method would be sand blind, DPM, slab, DPM, PIR + UFH pipes, screed. However, I proposed a build up of:

 

• Sand blind
• DPM
• PIR
• DPM
• UFH pipes
• 100mm fibre-reinforced slab
• Underlay
• LVT

 

Architect and BC are happy with this (architect said it's a common commercial build-up) but the builders are not and reckon it's not the right way. I don't see much point in spending £5K on screed (it's a reasonable area) if we don't need it and I can fill the 75mm that we would have screeded with more (cheaper) insulation. I was hoping I could powerfloat the slab to get the snots off enough for underlay but am I being a bit naïve?

 

Any advice would be much appreciated.

Edited October 19, 2023 by Ben Weston

[jayc89]

Thanks exactly how I'm doing my next slab. 

[Ben Weston]

5 minutes ago, jayc89 said:

Thanks exactly how I'm doing my next slab. 

 

The builders and other trades I speak to on site don't get it but I have come up against this "we've always done it this way..." attitude throughout this project. I don't really see the difference if the insulation values are there and the type 1 and sand is well compacted. The floor isn't structural. I realise a finished concrete slab won't have the mirror finish of a flow screed but surely powerfloating it will get it flat enough to accept the underlay and LVT?

 

Genuine question as I've not personally seen it done this way.

Edited October 19, 2023 by Ben Weston

[jayc89]

1 minute ago, Ben Weston said:

 

The builders are other trades I speak to on site don't get it but I don't really see the difference if the insulation values are there and the type 1 and sand is well compacted. The floor isn't structural. I realise a finished concrete slab won't have the mirror finish of a flow screed but surely powerfloating it will get it flat enough to accept the underlay and LVT?

 

Genuine question as I've not personally seen it done this way.

 

Haven't done it yet, so can't really comment. The last concrete floor I had laid as a sub-floor, was quite rough and needed a bit of work to accept the PIR, so I wouldn't fancy that as my finished floor, but the guy who did my screed can also pour a 10mm flowing aggregate which I suspect will be much smoother. 

[Ben Weston]

Just now, jayc89 said:

 

Haven't done it yet, so can't really comment. The last concrete floor I had laid as a sub-floor, was quite rough and needed a bit of work to accept the PIR, so I wouldn't fancy that as my finished floor, but the guy who did my screed can also pour a 10mm flowing aggregate which I suspect will be much smoother. 

 

Interesting. So you're essentially having a mini-screed on top? 

[joe90]

13 minutes ago, Ben Weston said:

"we've always done it this way..." attitude throughout this project.

So common and a shame some builders can’t move with the times, insist on your way if your happy, architect is happy  and your BC is happy then crack on, perhaps your builder will learn something in the process. If not find someone else  with an open mind.

[JohnMo]

We have a similar buildup, but with a 150mm of steel reinforced concrete below the PIR. We did our floor with fibre reinforced concrete, 100mm thick with UFH pipe stapled to the PIR, finish was power floated, then either tiles bonded oak floor or carpet. Had to do some self leveling compound here and there.

 

Aim for about 200mm of PIR insulation. 

[Canski]

1 hour ago, Ben Weston said:

I realise a finished concrete slab won't have the mirror finish of a flow screed but surely powerfloating it will get it flat enough to accept the underlay and LVT?

 

 

Power floated concrete is only as good as it is laid. The poweefloat simply polishes the surface and if done correctly the poweefloat doesn't touch the floor until you can walk on it leaving only minor footprints. As many here know who have poured concrete floors it is quite difficult to get it to finished floor standards of accuracy.

[Ben Weston]

3 minutes ago, Canski said:

Power floated concrete is only as good as it is laid. The poweefloat simply polishes the surface and if done correctly the poweefloat doesn't touch the floor until you can walk on it leaving only minor footprints. As many here know who have poured concrete floors it is quite difficult to get it to finished floor standards of accuracy.

 

Thanks. Yeah, I think that's the bit I need a bit more understanding on. Not expecting a 'finished floor' standard but something smooth enough to accept underlay and LVT on top. If it needs a layer of floor levelling compound over the top, this would still be cheaper than a screed from the looks of things.

[Ben Weston]

1 hour ago, JohnMo said:

We have a similar buildup, but with a 150mm of steel reinforced concrete below the PIR. We did our floor with fibre reinforced concrete, 100mm thick with UFH pipe stapled to the PIR, finish was power floated, then either tiles bonded oak floor or carpet. Had to do some self leveling compound here and there.

 

Aim for about 200mm of PIR insulation. 

 

Is your floor structural? Was there any reason you effectively went for two slabs? 

[joe90]

22 minutes ago, Ben Weston said:

If it needs a layer of floor levelling compound over the top, this would still be cheaper than a screed from the looks of things.

+1 👍

[Chanmenie]

My floor is exactly as your proposed.

It will work fine, I have not tried the heating in my new build yet as only just got the roof of on, but the house where I currently live is on an estate with several hundred house all built with UFH pipes in 4” - 6” slabs and the ufh works fine.

But I too have been told it won’t work  

[Ben Weston]

10 minutes ago, Chanmenie said:

My floor is exactly as your proposed.

It will work fine, I have not tried the heating in my new build yet as only just got the roof of on, but the house where I currently live is on an estate with several hundred house all built with UFH pipes in 4” - 6” slabs and the ufh works fine.

But I too have been told it won’t work  

 

Good to know, thanks. You're in our neck of the woods too - we're just south of Norwich!

[JohnMo]

52 minutes ago, Ben Weston said:

 

Is your floor structural? Was there any reason you effectively went for two slabs? 

Yes a structural floor, as the house is built on a sand hill.

[Chanmenie]

On 19/10/2023 at 14:06, Ben Weston said:

 

Good to know, thanks. You're in our neck of the woods too - we're just south of Norwich!

Hi Ben 

yeah I’m south of Norwich at Poringland, I live in a Norfolk Homes built house, they have been putting UFH pipes in the slabs for years. The only problem I’ve heard of was a customer putting high tog carpets in with stopped the heat getting through. 
Who’s doing the fibre reinforced slab for you ?

I had Co-Dunkall do mine with Eastern Concrete EC flow, it dried pretty smooth as it’s self compacting.

you’re welcome to have a look