UFH in slab or screed, eps or pir insulation?

[Tin Soldier]

Hi there,

 

I've a 125m2 extension being erected next year with a pretty basic floor slab planned.

 

Floor covering

65mm Screed

UFH Pipwork

150mm PIR insulation

100mm c35 concrete with mesh

 

Whilst looking at the overall prices of each piece of work there's a couple of questions that have come up

would it beneficial to change the floor structure to incorporate circa 250mm of eps insulation under the concrete slab, instead of the 150mm pir above slab.

And whilst I am at it, possible to incorporate the Under floor heating pipework into the slab, as opposed to having the pipework in a screed on top of the slab?

 

The reason for looking at this is to save time and money.

The 250mm of eps insulation has similar u value to 150mm pir, whilst being cheaper - circa 1k at the moment, but there is another price increase on pir due in February.

 

If I incorporated the pipework into the slab, I could save circa 4k for the screed work post panel installation, but it would also mean I could crack on with the studwork immediately after the kit erection as opposed to laying pipework and ordering in self levelling screed.

 

any thoughts/drawbacks?

[Nickfromwales]

More insulation, and put the reinforced slab as your finished floor with the UFH pipes attached to the mesh.? Do away with the screed and have a much more efficient floor to boot with the extra insulation . 

Go for 100mm of PIR, over 100mm of EPS and have the DPM under the PIR. Lay the EPS over your levelled and compacted type one and no need for loads of blinding with sand other than to fill any troughs in the type one after whacking 

 

[chrisb]

I've just done this - see other thread that I can't link to on my phone :-(

Don't underestimate the work involved in cable-tying UFH pipe to mesh.

Also, walking on the mesh (necessary to install pipe) caused it to bend and lift in places. The builder and concrete chap were concerned about it rising up when the concrete was being laid. We had a 120mm slab. In the end, the whole thing took an extra 2m3 of concrete as the EPS underneath compessed, so the actual thickness is a bit more than 120mm.

Perhaps consider 150mm slab thickness so you have no worries about covering the mesh/pipes?

 

Chris

 

[Onoff]

- Compacted Type 2 (home made, hardcore graded through a 40mm sieve).

- Sharp sand blind

- 25mm EPS

- DPM

- 150mm PIR (100 then 50)

- Polypipe tray with 16mm UFH Pex-Al-Pex

- A142 mesh

- 100mm concrete

 

...s'what I've done.

 

If I could have been ar$ed digging deeper I'd have thickened up on the PIR. 

 

[Nickfromwales]

The EPS won't compress as it should be EPS 100 ( not 70 ), so my money is on the groundworks having not been prepared properly / fully. . 

If the ground is compacted with grade 3 stone, then topped with type one, whacked thoroughly as it's being layered, and then blinders with a sand layer it'll simply never compress to that degree, certainly not 20mm. Laying 150mm of wet concrete will also weigh a hell of a lot more and consume a lot more volume than the required 100mm. Many here have gone for 100mm reinforced slab without issue, plus pex-al-pex UFH is pretty solid stuff which my screeders regularly wheel full wheelbarrows of screed over and walk upon without issue. Striking the pipe of stepping on it where it is not supported by the rebar is of course a daft thing to do, so it's down to the care and diligence of the contractor to be careful, and down to you to be there to enforce this in what will be one of the most important parts of the build. 

Absolutely no need for 150mm of reinforced concrete afaic, so focus on the prep work and the rest will be relatively easy / straightforward. 

[Tin Soldier]

thanks for the replies guys

 

Could I ask what the reason for recommending 100mm or eps then 100mm of pir? as opposed to 250mm of eps100?

[jfb]

its 6.25m3 less material to dig out/dispose of! depends on what you can do with that material I guess

[Nickfromwales]

1 hour ago, Tin Soldier said:

thanks for the replies guys

 

Could I ask what the reason for recommending 100mm or eps then 100mm of pir? as opposed to 250mm of eps100?

In the previous text you won't get 250mm in unless its excavated more.  The mix of insulation type is cheaper and still has a very good u value plus I always favour EPS against Mother Earth as it's will conform to the surface better. I also put the DPM above the first layer of EPS and under the pir so it's protected against puncturing. 

If you can get 250mm of EPS in then go for 150 EPS and 100 pir just for the better u value. 

[chrisb]

Depending on when you intend to do this, you may encounter supply issues with both EPS and PIR. This has been the case over the last month or so with my extension.

I have 250mm EPS in the new extension and 150mm PIR in the existing kitchen (floor dug up and replaced).

[Tin Soldier]

 ok I'll have a think,

 

I have me own digger to excavate and lots of land to distribute material on, so more than happy to dig.

[Bitpipe]

8 minutes ago, chrisb said:

Depending on when you intend to do this, you may encounter supply issues with both EPS and PIR. This has been the case over the last month or so with my extension.

I have 250mm EPS in the new extension and 150mm PIR in the existing kitchen (floor dug up and replaced).

 

Is there a shortage? Does this mean I can finally cash in on the 5 sheets of 200mm EPS70 in my garden? Almost as good as Bitcoin...

 

[chrisb]

2 minutes ago, Bitpipe said:

 

Is there a shortage? Does this mean I can finally cash in on the 5 sheets of 200mm EPS70 in my garden? Almost as good as Bitcoin...

 

 

Take it to the car park at Selco in Slough and someone will rob you pay good money for it!

 

Seriously, take a look at eBay. There was hardly anything around when I was looking a month ago.

Edited November 3, 2017 by chrisb
Addition of potentially useful information, rather than soley a facetious comment

[Jeremy Harris]

2 hours ago, chrisb said:

I've just done this - see other thread that I can't link to on my phone :-(

Don't underestimate the work involved in cable-tying UFH pipe to mesh.

Also, walking on the mesh (necessary to install pipe) caused it to bend and lift in places. The builder and concrete chap were concerned about it rising up when the concrete was being laid. We had a 120mm slab. In the end, the whole thing took an extra 2m3 of concrete as the EPS underneath compessed, so the actual thickness is a bit more than 120mm.

Perhaps consider 150mm slab thickness so you have no worries about covering the mesh/pipes?

 

Chris

 

 

 

Something seriously awry, there.  Our slab is 100mm, laid on 300mm of EPS 100, with mesh.  The UFH pipes are tied to the mesh.  At a guess it took two guys maybe half a day to lay and secure the UFH pipe, if that.  There was zero movement in the mesh or the EPS, everything stayed dead flat, and there was no extra concrete used.  Here are the photos:

 

 

 

Edited November 3, 2017 by JSHarris

[chrisb]

The issue seemed to arise because when standing on the mesh, even without the UFH pipe attached, it gets bent a small amount (as it's held on 50mm chairs). This tends to lift the edges of the mesh upwards where it pivots on the chair. After attaching the UFH pipe, this is then harder to level out as there is now pipe tied to the mesh on one side, holding it in that position.

 

In the end, there is no UFH pip, or mesh at the surface, so I think all is fine.

[Jeremy Harris]

10 minutes ago, chrisb said:

The issue seemed to arise because when standing on the mesh, even without the UFH pipe attached, it gets bent a small amount (as it's held on 50mm chairs). This tends to lift the edges of the mesh upwards where it pivots on the chair. After attaching the UFH pipe, this is then harder to level out as there is now pipe tied to the mesh on one side, holding it in that position.

 

In the end, there is no UFH pip, or mesh at the surface, so I think all is fine.

 

 

If you look closely, you'll see that the chairs were temporarily pulled out from the areas where pipe was being laid, then the mesh was lifted back up on to them afterwards.  Get's around the problem and makes the job easier and quicker.

[Tin Soldier]

those are really great pictures to see JSHarris

 

so heres another probably naïve question

 

If my 100mm slab is sitting on top of 250mm eps insulation, how to do you inslate the side of the slab from the blockwork.

 

I assume insulation and looking at my current drawings its noted as 30mm Kingspan tw55 upstand for self leveling screed. is this enough or should it be wider, and if it is wider, how does that effect the studwork/battening that I guess would be going directly above it?

[Jeremy Harris]

Ours is a passive slab, so the outer 2/3rds of the 300mm thick frame sits over a 200mm wide EPS 100 upstand, with only the inner 100mm of the frame (the load bearing part) sitting on the warm, reinforced concrete, ring beam around the edge of the slab.  This means the edge of the slab has 200mm of insulation all around it, which pretty much prevents any heat loss out sideways.

 

For other build methods you have to come up with ways of mitigating the edge loss and thermal bridging that can occur, and a great deal depends on the exact detail of your build.

[TerryE]

I have the same system as Jeremy. Once the crew know how to do it, then they make it look easy and you have to wonder why it isn't the standard way of doing it. It is cheap to do and very effective.

 

The answer, in my opinion, is training and skills or the lack  thereof. Why use a new more effective approach it requires learning something new when the customer will end up paying for it anyway?

 

[Tin Soldier]

eps70 or eps100 for under slab insulation?

 

I'm finding mixed views when I try and search the answer

[jack]

It probably depends what's going on top.

 

We have EPS 100 under most of our MBC slab, with EPS 300 under the ring beam and areas of high load. That's a structural slab though, which has to handle the weight of the entire house.

 

I haven't read everything above, but if it's just a floor slab that isn't bearing any walls, EPS 70 may be fine. That said, it depends very much on what you're actually doing - I'd be checking with your engineer or the suppliers (and building control officer) for advice before committing to a solution.

[Tin Soldier]

its just a slab,

 

sips panels sitting on blockwork on strip foundations.

 

I've asked the architect who will check with the engineer as I'm changing the floor make up

 

struggling to find eps100 in stock at a reasonable price though

[Bitpipe]

It's quite straightforward - you get your SE to calculate the point loading of the structure  and then choose the EPS that meets or just exceeds it.

 

http://jablite.co.uk/wp-content/uploads/2016/01/Jablite-EPS.pdf

 

 

 

 

 

[Tin Soldier]

SE has come back with weight of slab is 500kg per m2, equating to 5Kpa

 

no issue with any type of insulation that I have suggested (eps70, 100 or PIR)

[A_L]

6 hours ago, Tin Soldier said:

eps70 or eps100 for under slab insulation?

 

I'm finding mixed views when I try and search the answer

 

eps 70 has a 1% compressive strength of about 20kPa, 150mm of concrete exerts a force of about 0.150*2500*9.81=3.7kPa so as long as nothing else involved its O.K.

KayMetzler EPS.pdf

[Tin Soldier]

its a 100mm slab with mesh and ufh pipes