insulation under screed

babybuilder

Hi,

I have decided to place 125 mm kingspan floor insulation on top of the 150mm subfloor of my new build. Then I want to place 75mm or 100mm of screed on top of this. Has anyone out there done this and what type of screed or even concrete would be needed. I have been told by someone that I may have to place reinforced concrete screed over the 125 mm insulation. I would be grateful for any advise on this matter.

Thanks

Viking House

Hi Babybuilder,

Here is my opinion!

I don't think that Polyeurethene is suitable for insulating under or between concrete slabs for the following reasons.
The U-value of Kingspan gets worse over time as the trapped Pentane gas migrates out of the insulation.
The Lambda value is 0.015 when it leaves the production plant and 28 days later the Lambda value has deteriorated to 0.025 which is the Lambda value that the product is marketed at. What happens 28 months later? This can be seen easily when you break open a piece of fresh Kingspan and put a cigarette lighter near it (it flames up) and do the same with an old piece of Kingspan (no reaction).

Kingspan is not a good product in the floor as the U-value also deteriorates considerably when it gets wet as it soaks up water.
On the Kingspan Agreament Cert you are suppose to put plastic under the insulation which becomes the condensation point where all the moisture is trapped making the insulation wet.

When you pour concrete directly onto foil-back Kingspan the foil reacts with the concrets and dissolves letting the insulating gas escape, letting the water from the cement direct access to the Polyeurethene reducing the U-value even more.

The Dew Point (condensation) occurs on the outer 10-15mm of Kingspan and the Concrete being not very breathable allows this moisture to build up at this point making the insulation even more wet.

babybuilder

Thanks Viking house
I've heard of this off-gassing before with this type of insulation. Can you suggest a replacement insulation for this situation?

Viking House

Polysterene is the best one for the foundations but you should use at least 250mm.

muffler

Viking House wrote:

Hi Babybuilder,

Here is my opinion!

I don't think that Polyeurethene is suitable for insulating under or between concrete slabs for the following reasons.
The U-value of Kingspan gets worse over time as the trapped Pentane gas migrates out of the insulation.
The Lambda value is 0.015 when it leaves the production plant and 28 days later the Lambda value has deteriorated to 0.025 which is the Lambda value that the product is marketed at. What happens 28 months later? This can be seen easily when you break open a piece of fresh Kingspan and put a cigarette lighter near it (it flames up) and do the same with an old piece of Kingspan (no reaction).

Kingspan is not a good product in the floor as the U-value also deteriorates considerably when it gets wet as it soaks up water.
On the Kingspan Agreament Cert you are suppose to put plastic under the insulation which becomes the condensation point where all the moisture is trapped making the insulation wet.

When you pour concrete directly onto foil-back Kingspan the foil reacts with the concrets and dissolves letting the insulating gas escape, letting the water from the cement direct access to the Polyeurethene reducing the U-value even more.

The Dew Point (condensation) occurs on the outer 10-15mm of Kingspan and the Concrete being not very breathable allows this moisture to build up at this point making the insulation even more wet.

A lot of companies manufacture and supply polyeurethene insulation slabs and I fail to see what makes Kingspan any different from the rest.

All these products are certified based on tests of the highest calibre so I fail to see how you can find fault with this Kingspan product when the NSAI doesnt.

I dont understand where you are getting all this "moisture" from. As with any type of polyeurethene insulation for floors it is clearly specified that construction water and screeds be allowed to dry prior to fixing the insulation. In any event the moisture will be insignificant within a couple of days. If you use the same analogy re moisture then kitchen/bedroom units or furniture etc will never be in a house because of their high moisture absorbency capacity.

Viking House

Hi Muffler

muffler wrote:

A lot of companies manufacture and supply polyeurethene insulation slabs and I fail to see what makes Kingspan any different from the rest.

I didn't mean to single out Kingspan, its the product that the OP mentioned and I continued with it. All Polyeurethene insulations have these problems.

muffler wrote:

All these products are certified based on tests of the highest calibre so I fail to see how you can find fault with this Kingspan product when the NSAI doesnt.

Partial fill cavity walling is certified and it is impossible to reach the U-values stated with the system because of Cold Bridging and Thermal Looping.
Most certified TF manufacturers put the OSB to the outside which is clearly a bad practice so I don't have much faith in the Certification process.

muffler wrote:

I dont understand where you are getting all this "moisture" from. As with any type of polyeurethene insulation for floors it is clearly specified that construction water and screeds be allowed to dry prior to fixing the insulation. In any event the moisture will be insignificant within a couple of days. If you use the same analogy re moisture then kitchen/bedroom units or furniture etc will never be in a house because of their high moisture absorbency capacity.

Poured vibrated concrete is not very breathable and takes 10-12 months to properly dry out if it is not surrounded by plastic.
When you trap wet Polyeurethene between plastic and non breathable concrete how is it suppose to dry out?
Kingspan state that the product should not be used if it gets wet.
The moisture comes from the concrete and from the occupants in the house.

lfcjfc

What about phenolic based rigid insulation, do they suffer from the same problems?

Mellor

Viking House wrote:

The Dew Point (condensation) occurs on the outer 10-15mm of Kingspan and the Concrete being not very breathable allows this moisture to build up at this point making the insulation even more wet.

Where the dew point occurs depends on the lambda values, thickneses and temperatures, no area is prone to becoming a dew point, it could be any where in the material, or even outside it. Material does not affect the position of the dew point.
For optimum results the insulation should have plastice on both sides.

Viking House

Mellor wrote:

For optimum results the insulation should have plastice on both sides.

That just gives more places for moisture to be trapped.
The best way is to use Polysterene 200mm+ on top of crushed stone 18-35mm and put the concrete on that.

babybuilder

Thanks Viking house et al

I've considered placing the insulation under the subfloor but feel that the total depth of slab + screed, 225-250mm, is too much thermal mass to heat. I suppose that if our climate was more extreme then it would be better. However, imo, having the insulation under 75-125mm of screed/concrete makes more sense in that it can respond to quicker changes in temperature.

My main concern though is the stability of the screed/concrete. Should I use a thin metal mesh or, as someone suggested, a concrete-plastic fibre mix? I would be grateful if there is anyone who has experience of using these types of screed.
Thanks

Viking House

babybuilder wrote:

I've considered placing the insulation under the subfloor but feel that the total depth of slab + screed, 225-250mm, is too much thermal mass to heat. I suppose that if our climate was more extreme then it would be better. However, imo, having the insulation under 75-125mm of screed/concrete makes more sense in that it can respond to quicker changes in temperature.
My main concern though is the stability of the screed/concrete. Should I use a thin metal mesh or, as someone suggested, a concrete-plastic fibre mix?

You don't need that much (250mm) concrete at all babybuilder. 100mm of vibrated concrete with UF heating pipes and steel mesh is sufficient in most circumstances on top of 300mm of Polysterene.
150mm of concrete if you have a raft foundation. Its easier to level the floor when the walls aren't in the way.

FWIW, I went for 100mm concrete with A143 steel mesh & UFH over 200mm of polystyrene. I was a bit worried about using any thicker in case of stability problems.

ircoha

Deleted User wrote:

FWIW, I went for 100mm concrete with A143 steel mesh & UFH over 200mm of polystyrene. I was a bit worried about using any thicker in case of stability problems.

db and vh:
Just wondering where the mesh is positioned vis-avis the UFH pipes, I recall reading elsewhere on this site that the mesh needs to be positioned near the top of the slab or is it done in 2 goes, the first slab with the mesh and then the UFH pipes laid on this slab?

The other point is that thermal bridging should be avoided between the subfloor and the slab.
I think that VH has some stuff on this on his site

Viking House

ircoha wrote:

Just wondering where the mesh is positioned vis-avis the UFH pipes, I recall reading elsewhere on this site that the mesh needs to be positioned near the top of the slab or is it done in 2 goes, the first slab with the mesh and then the UFH pipes laid on this slab?

The pipes go down first, held in place with a plastic channel with grooves cut out of them. Then place shoes between the pipes on the Polysterene that keep the Steel up 80mm, so the steel sits near the top of the slab.

BoylerMan

VH
Have you (or anyone) had any experience using fibers (as asked above) in a (sand/cement) screed in place of the mesh?
I used fibers in the subfloor which I was advised would give superiour strength to mesh. Cost is not too bad for fibers at 10Euro/m3 extra. Surface finish looks hairy even after powerfloating. I am currently building a 3500 sq ft Dormer with UFH both upstairs and downstairs and am about to start the UFH in about 2 weeks. I am trying to make the screed pour as simple as possible and fibers will help eliminate cutting up meash and tripping over mesh when tamping.

galwaytt

I have 70mm of sand/cement screed on 150mm Dow LB-X downstairs, and 70mm of sand/cement screed on 30mm LB-X on a timber deck, upstairs.

I see no merit in this climate of more than 150mm insulation on ground floor, and screed depths (given our mild climate) of 70-80mm is plenty.

I have UFH in my house for nearly 10 years now.

ircoha

ircoha wrote:

db and vh:
Just wondering where the mesh is positioned vis-avis the UFH pipes, I recall reading elsewhere on this site that the mesh needs to be positioned near the top of the slab or is it done in 2 goes, the first slab with the mesh and then the UFH pipes laid on this slab?

I have the mesh about half way down and the ufh pipes tied to the top of this mesh, a centrally placed mesh provides maximum strength to the slab & pipes as near to the top as is practabley (SP) possible for better heat transfer.

babybuilder

Hi

Spoke to tecnical department of kingspan re tf70 125mm insulation. For under screed use: Must have from ground up: dpm(under subfloor in this case), insulation, plastic vapour check, sand-cement screed or fibre-concrete. No mention of reinforced concrete screed. This will give calculated u-value of 0.14 assuming 0.14 m-1 P/A and use of edging insulation.

{This floor detail i.e. insulation above subfloor, is supposed to be suitable for non-constant house heating or occupancy.}

However, my architect will still have a bee in his bonnet about this as he is insistent about using a wire mesh in the screed/concrete finish.
We'll see.

Stell mesh will certainly reduce the risk of cracking, it depends on how large the slab is. In my house the slab is a single cast with "crack lines" splitting it into four pieces each approx 8m x 6m in size to allow for contraction.

galwaytt

mesh in a floor screed is over-kill for domestic applications. Unless it's a colossal room. Aircraft hanger ?

galwaytt

galwaytt wrote:

mesh in a floor screed is over-kill for domestic applications. Unless it's a colossal room. Aircraft hanger ?

Agreed! But I was using it mainly as a mounting for the UFH pipes (I suppose I could have used polypropeline mesh instead).

galwaytt

aaah, I see what you mean. Well there is a plastic clip system and a plastic rail you can use, just put down on top of your insulation, and the pipe, er - clips :rolleyes: - into it.

No need for mesh, then - it's bloomin' awkward, anyway.

Viking House

babybuilder wrote:

Spoke to tecnical department of kingspan re tf70 125mm insulation. For under screed use: Must have from ground up: dpm(under subfloor in this case), insulation, plastic vapour check, sand-cement screed or fibre-concrete. No mention of reinforced concrete screed. This will give calculated u-value of 0.14 assuming 0.14 m-1 P/A and use of edging insulation.

I don't agree with Kingspan on this build up, I think it is flawed.
An Architect friend of mine was fitting new Combi Boilers to an apartment block in London and they had to core through the poured Concrete walls to fit the Flues.
In the middle of the mass concrete walls was a layer of Polysterene. When the guy finished coreing one of the holes my friend picked up the Polysterene core that fell out of the drill. It was like a sponge full of water when he squeezed it. The dew point was at the centre of the wall and the non-breathable dense poured concrete never allowed the wall to dry out. It was like injecting water into the wall under pressure.
Putting Kingspan between two layers of concrete with plastic at both sides of the insulation will have an even worse effect as Kingspan sucks up water like a sponge while Polysterene has a good resistance to moisture in normal conditions.

ennisjim

Viking House wrote:

Kingspan sucks up water like a sponge

Don't agree with this. During my build the insulation (Xtratherm in my case but probably same as Kingspan) in cavity was left exposed to terrible weather last autumn/winter for weeks and weeks. I was concerned that the insulation would act as a sponge and you would think it was if you felt the first few mm's of exposed insulation, but when I cracked some open it was perfectly dry below the surface.