Floor build up for ground floor UFH

[vala]

Should be starting a little extension which will form part of the UFH on the ground floor. Plan is to have the existing slab taken up, dug down, insulation and a new slab with UFH within. Plan is for the finished floor to be polished concrete but just the 'cream' standard.

I need to discuss with the builder but from info I've read on here and other sources, I thinking of a baseline to be:

hardcore compacted,

sand binding,

200mm PIR,

UFH on mesh,

100mm concrete slab.

 

Would this be ok? Or should I be looking into other thicknesses of concrete, different amount of insulation, different insulation, UFH clipped onto PIR instead of tied to mesh, etc etc?

 

Any help would be much appreciated.

[PeterW]

Why mesh ..? What size is the slab..?

 

if no differential movement I would just go with 100mm slab and make sure there are no stress points such as changes in depth of the hardcore.

[vala]

24 minutes ago, PeterW said:

Why mesh ..? What size is the slab..?

 

if no differential movement I would just go with 100mm slab and make sure there are no stress points such as changes in depth of the hardcore.

builder mentioned it when we were discussing floor build up due to the UFH.

not set on using it, just looking at other option and then will discuss with him.

if we can lose the mesh then great, and can then just clip the pipe work to the PIR.

 

slab is only circa 55sqm.

[HughF]

I went with clips, as I have them… only 16m2 though. 
 

hardcore, sand blind, bag, 240pir, bag, 125 conc.

Edited June 28, 2023 by HughF

[ColdHouse]

On 27/06/2023 at 22:24, vala said:

Should be starting a little extension which will form part of the UFH on the ground floor. Plan is to have the existing slab taken up, dug down, insulation and a new slab with UFH within.

 

Do you mind me asking how much your builder has quoted to dig up the existing slab and replace with UFH?
Is it going to be a lengthy process?

I'm considering doing the same - existing ground floor slab is ~75m²  with ~25m²  extension. 

[vala]

On 29/06/2023 at 21:28, ColdHouse said:

Do you mind me asking how much your builder has quoted to dig up the existing slab and replace with UFH?
Is it going to be a lengthy process?

I'm considering doing the same - existing ground floor slab is ~75m²  with ~25m²  extension. 

no idea on this yet.

first thing is to get the shell of the extension done. Hopefully he fits us in this year, then once the weather warms up next year we'll have the slab in the house sorted.

[HughF]

36 minutes ago, vala said:

no idea on this yet.

first thing is to get the shell of the extension done. Hopefully he fits us in this year, then once the weather warms up next year we'll have the slab in the house sorted.

Time and materials I guess...?

[Dave Jones]

what m2 is extension ? block and beam may be faster.

[vala]

On 30/06/2023 at 22:23, HughF said:

Time and materials I guess...?

yeah, it'll be the same builder so sure he'll some idea when he does the first part.

On 01/07/2023 at 07:14, Dave Jones said:

what m2 is extension ? block and beam may be faster.

Tiny, 9sqm. Literally just for a downstairs loo.

[vala]

So looks like polished concrete may off be table now, so the back up option is to go tiles.

Spoke to my tiler who noted that if the UFH pipes were installed above the slab, on clips or in trays, they could lay a 60-65mm screed and then tile on this (with the use of a decoupling mat).

However also seen I could install the pipes on the insulation, have the slab poured, then look to have the tiling done.

 

Is there any benefit to either option and would one be suited more depending on house make up? For reference its a 70's built semi detached with ~65mm cavities which will be filled with beads. Aside from the 200mm PIR which will be under the ground slab, first floor has UFH in a pug mix, and loft has ~250-300mm insulation.

[JohnMo]

 

10 minutes ago, vala said:

UFH pipes were installed above the slab, on clips or in trays, they could lay a 60-65mm screed and then tile on this

Doesn't that just add more expense for little or no benefit.

 

Staple UFH pipes to the PIR, then fibre reinforced concrete, tile to concrete

 

So

hardcore compacted,

sand binding,

DPM

200mm PIR,

Polythene separating layer

UFH stapled to PIR,

100mm fibre reinforced concrete slab.

 

 

 

[vala]

1 minute ago, JohnMo said:

 

Doesn't that just add more expense for little or no benefit.

 

Staple UFH pipes to the PIR, then fibre reinforced concrete, tile to concrete

 

So

hardcore compacted,

sand binding,

DPM

200mm PIR,

Polythene separating layer

UFH stapled to PIR,

100mm fibre reinforced concrete slab.

 

 

 

 

Hi, the pipes in trays, and screeded over was mentioned to me by the tiler. But I would much rather lose the screed if possible, maybe have to have a latex poured in case if the concrete isn't flat enough for the tiler but I'll let them deal with that.

I just wasn't aware whether the different options would suit different house make ups?

But yes, if the above is suited for the house then I'd rather go with that.

[Dave Jones]

why do you want to lose the screed its your finished floor ?

 

pipes stapled to the insulation then 75mm sand/cement screed on top.

[jayc89]

On 27/06/2023 at 23:07, PeterW said:

Why mesh ..? What size is the slab..?

 

if no differential movement I would just go with 100mm slab and make sure there are no stress points such as changes in depth of the hardcore.

 

My understanding was that mesh was sat on "shoes" to leave it middle of the slab, which also means the pipework is central, not having to work its way up from the bottom before the users feel any benefit. 

[vala]

4 hours ago, Dave Jones said:

why do you want to lose the screed its your finished floor ?

 

pipes stapled to the insulation then 75mm sand/cement screed on top.

Thought on losing screed to save on how much to dig up.
Current potential build up is as per @JohnMo's reply above. Then with tiles on top.

[crooksey]

How old is your existing house? Are you sure you have a structural slab and not a floor screed?

 

Screed over PIR is generally a better option for a retro fit, and screeds also offer better thermal conductivity, personally I am not a fan of liquids, but look at modified sand and cement screeds, like Mapei Topcem or PCT Xtreme. 

[vala]

9 hours ago, crooksey said:

How old is your existing house? Are you sure you have a structural slab and not a floor screed?

 

Screed over PIR is generally a better option for a retro fit, and screeds also offer better thermal conductivity, personally I am not a fan of liquids, but look at modified sand and cement screeds, like Mapei Topcem or PCT Xtreme. 

house was built in the 70's.

haven't yet confirmed whether there's a structural slab or screed currently in place.

[LiamJones]

On 26/07/2023 at 06:42, Dave Jones said:

pipes stapled to the insulation then 75mm sand/cement screed on top.

Im a bit confused by this, is a concrete slab not required? I’ve always though it’s was 100mm min concrete slab (either over or under insulation) plus 70mm ish of screed on top?

[PeterW]

20 hours ago, LiamJones said:

Im a bit confused by this, is a concrete slab not required? I’ve always though it’s was 100mm min concrete slab (either over or under insulation) plus 70mm ish of screed on top?

old school design - you can put all the concrete on top of the insulation and put the UFH in that and creates one big storage heater. Just need to get your internal floor levels right from the outset 

[LiamJones]

2 hours ago, PeterW said:

old school design - you can put all the concrete on top of the insulation and put the UFH in that and creates one big storage heater. Just need to get your internal floor levels right from the outset 

so if you go 100mm slab on top of insulation you don’t need screed? Is it decent enough to tile on (if done well)?

[JohnMo]

6 minutes ago, LiamJones said:

so if you go 100mm slab on top of insulation you don’t need screed? Is it decent enough to tile on (if done well)?

Yep no issue. We did our finished floor before the walls got built. A few low spots were sorted with a few bags of self leveling screed.

[HughF]

Hardcore-> PIR -> bag -> pipes in 125mm conc…

 

No need for screed.

[LiamJones]

On 06/08/2023 at 20:26, HughF said:

Hardcore-> PIR -> bag -> pipes in 125mm conc…

 

No need for screed.

hi @HughF, I’m getting closer to this and learning more. I’m now trying to work out the spec for the concrete that UFH is laid in. Some do 100mm, some more. Some use rebar, some use fibre, some use none. 
 

Can you shed any light on your choice to use 125mm concrete with no reinforcement? 

[HughF]

10 hours ago, LiamJones said:

hi @HughF, I’m getting closer to this and learning more. I’m now trying to work out the spec for the concrete that UFH is laid in. Some do 100mm, some more. Some use rebar, some use fibre, some use none. 
 

Can you shed any light on your choice to use 125mm concrete with no reinforcement? 

We’re on stable ground, I was going to go with 100mm but my builder suggested 125mm would be better.

 

We just used regular concrete as that’s what we’ve always done for slabs. Perhaps if it was bigger we would have put some control joints in it along with a bit of mesh.

 

[Dave Jones]

On 06/08/2023 at 20:26, HughF said:

Hardcore-> PIR -> bag -> pipes in 125mm conc…

 

No need for screed.

 

only issue will be it wont be flat enough to put a floor on no matter how much you float it. Screed is.