250mm insulation under UFH slab

[Tetrarch]

Hi,

 

I have now removed floorboards and joists in the lounge and have a hole to fill (actually 2 when the dining room is completed). I am looking at a 20mm Eng Wood Floor on top of a 70mm UFH slab and thus have ~30 sq m of 250mm depth to insulate.

 

What is the most economical and effective way to fill this 250mm? After a little research I believe I have three alternatives.

 

A bespoke 250mm Jabfloor EPS (or similar)

 

Layers of off-the-shelf Jabfloor EPS to reach the 250mm

 

A Jabfloor layer topped with a Celotex (or similar) overlay

 

I'm looking for any advice/experience or alternative recommendations

 

Regards

 

Tet

 

PS: Below is a floor schematic where the green is floorboards, the yellow (uninsulated) concrete (to be dug up and replaced) and the orange is the proposed new extension

 

 

[Nickfromwales]

250mm of EPS will be ample, and cheap. 300mm is heading for passive house standard levels of insulation. 
If you can get hold of seconds for the upper 150, then go for PIR ( celotex / kingspan etc ) and use 100mm EPS underneath. Or 150 EPS and 100mm PIR atop. Anything above EPS is a benefit, but I’d be more than happy with 250mm EPS tbh. 
Depending upon how you want to use the heating ( timed for working family / on long and low for retired ) then there could be argument for putting a slightly thicker screed down, but 70mm is a good average for this type of emitter and will give an even spread of heat output.

Edited March 1, 2021 by Nickfromwales

[tonyshouse]

70mm too thin, will crack. I like the idea of multiple layers of eps , you need a proper slab and for me that means min 100 thick concrete with anti cracking mesh and presumably ugh pipes in it too. Need perimeter insulation too pir? 

 

then min 4 months to fully dry out before laying wood on it 

[dpmiller]

2 minutes ago, tonyshouse said:

70mm too thin, will crack. I like the idea of multiple layers of eps , you need a proper slab and for me that means min 100 thick concrete with anti cracking mesh and presumably ugh pipes in it too. Need perimeter insulation too pir? 

 

then min 4 months to fully dry out before laying wood on it 

 

Poured thinscreeds don't crack at 70mm...

[Nickfromwales]

5 minutes ago, tonyshouse said:

70mm too thin, will crack.

You’ll get fractures from curing, but nothing that’s not expected. To say that will crack is a bit coarse a statement.

At 70mm I wouldn’t be laying a liquid screed anyway, I would be using a dry sand and cement screed.

No need for 4” thick reinforced concrete unless you’ve got very big rooms and no possibility of introducing relief joints at the doorways etc. The most important thing is to get the ground level, flat and true, and to apply a blinding layers of sharp sand over the compacted subfloor. 
Also remember the perimeter insulation up-stands, made from 25mm PIR for thermal break, and then a thin compressive strip of the small foam stuff to allow expansion.

If the subfloor prep is spot on, the floor won’t go anywhere. 

[Ian]

10 minutes ago, dpmiller said:

 

Poured thinscreeds don't crack at 70mm...

but it's not a screed.

Screeds are laid on top of a concrete floor (not 250mm of insulation)

[Russell griffiths]

Just now, Ian said:

but it's not a screed.

Screeds are laid on top of a concrete floor (not 250mm of insulation)

Not necessarily, I have a screed laid on top of eps insulation. 

It depends what is supporting the insulation. 

If the insulation is on top of compacted hardcore then I would use concrete with mesh reinforcement. 

If the insulation is over a concrete slab or block n beam then a screed.

 

Depends what is suppling the strength and support. 

 

@Tetrarch what is this insulation going down on to.  

[Ian]

15 minutes ago, Russell griffiths said:

Not necessarily, I have a screed laid on top of eps insulation. 

It depends what is supporting the insulation. 

If the insulation is on top of compacted hardcore then I would use concrete with mesh reinforcement. 

If the insulation is over a concrete slab or block n beam then a screed.

 

Depends what is suppling the strength and support. 

 

@Tetrarch what is this insulation going down on to.  

Sounds like @Tetrarch is infilling what used to be the void of a suspended timber floor so it's unlikely that the ground underneath will be properly compacted hardcore.

[Nickfromwales]

Doesn’t need to be compacted hardcore.

Needs to be sound and stable, and we obviously need a bit of feedback before saying more.

Ive done loads without, just a quick blinding and a whack and job done. What I do, ( if at all unsure of the subfloor ), is build up the 1st 50 / 75 / 100 with individual sheets of 25mm EPS so they can easily conform to the subfloor. 
DIY not here tbh, so one assumption is a builder with at least 3 brain cells will be employed and able to govern. But then again, you’d probably then end up with a 150mm slab, 50mm of insulation and 50mm liquid screed  

Edited March 1, 2021 by Nickfromwales

[Tetrarch]

Hi guys,

 

Thank you for the responses.

 

Floor is hundred year old concrete. It is a bit weird as it is light in colour the stones are larger than I would have thought is normal now, but it appears extremely solid. I attach a couple of pictures.

 

I am a DIY'er and the 70mm value is from my (likely) builder. His recommendation was to remove and use hardcore under a slimmer layer of PIR, but I went the whole hog and removed everything. Just to re-terate the measurements I have a tiled fireplace with a 100mm upstand. It is 300mm to the bottom of the vertical tiles so I was working on 250mm insulation + 70mm UFH screed + 20mm Flooring to bring the final floor level about half way up the tiles

 

Edit: UFH is for long and low as this is not for a working family, but newly retired

 

Regards

 

Tet

 

PS - look closely and you'll see that the double socket by the floor is actually connected by a bakelite junction box and a cooker switch plate - bodes well!  

Edited March 1, 2021 by Tetrarch

[Nickfromwales]

Ok, just for clarity, that concrete subfloor is staying yes? 
Be advised that EPS insulation CANNOT come into contact with the electrical cables. 

[epsilonGreedy]

33 minutes ago, Nickfromwales said:

Be advised that EPS insulation CANNOT come into contact with the electrical cables. 

 

 

Is that because of thermal concerns or do the two materials disagree with each other at a chemical level?

[TonyT]

Chemical level, EPS softens the plasticisers in the cable and the cable degrades 

[Nickfromwales]

2 hours ago, epsilonGreedy said:

 

Is that because of thermal concerns or do the two materials disagree with each other at a chemical level?

Chemical. The cause of a number of house fires. The plasticisers get absorbed and the cable insulation degrades to a point where it crumbles and falls away from the copper cores. 
Then ? 

[epsilonGreedy]

17 minutes ago, Nickfromwales said:

Chemical. The cause of a number of house fires. The plasticisers get absorbed and the cable insulation degrades to a point where it crumbles and falls away from the copper cores. 
Then ? 

 

 

Thanks. If EPS is traditional expanded polystyrene that when viewed close up can be seen to be comprised of fused together cellular nodules of polystyrene, do the other floor insulation materials (PIR and XPS) pose a similar danger?

 

[Nickfromwales]

5 minutes ago, epsilonGreedy said:

 

Thanks. If EPS is traditional expanded polystyrene that when viewed close up can be seen to be comprised of fused together cellular nodules of polystyrene, do the other floor insulation materials (PIR and XPS) pose a similar danger?

 

No, but another danger which is derating of the cables if they are not sheathed ( or protected by other such means of containment ). Conduit or other such containment is advised at that point. 

[ADLIan]

XPS will cause plasticiser migration in cables same as EPS - keep them apart!

[Tetrarch]

9 hours ago, Nickfromwales said:

Ok, just for clarity, that concrete subfloor is staying yes? 
Be advised that EPS insulation CANNOT come into contact with the electrical cables. 

 

Concrete subfloor is staying, electrical cables and microbore radiator pipework is most definitely going

 

Regards

 

Tet

[Nickfromwales]

Cool. 

[tonyshouse]

The concrete subfloor is likely to be insubstantial and not very flat or level, it could be only 50mm thick too 

[Nickfromwales]

11 hours ago, tonyshouse said:

The concrete subfloor is likely to be insubstantial and not very flat or level, it could be only 50mm thick too 

Doesn't matter, as it will make an excellent raft to sit the rest of the floor on. It's been in long enough to have settled, and will be fine to take the non point-load of a new upper deck. What's it like when you walk slowly over it? Any movement in the corners?  

[Tetrarch]

49 minutes ago, Nickfromwales said:

Doesn't matter, as it will make an excellent raft to sit the rest of the floor on. It's been in long enough to have settled, and will be fine to take the non point-load of a new upper deck. What's it like when you walk slowly over it? Any movement in the corners?  

 

Absoltely none.

 

May I pop back to my original question. The Jablite (no particular reason for choosing this brand, are others better/cheaper?) comes in standard thicknesses up to 200mm. Listening to the previous comments; to accomodate any unevenness I was thinking of getting a 50mm layer to get a proper level and then laying the 200mm on top - does that seem a sensible plan?

 

Do I need to tape the 50mm layer or just lay the 200mm at an offset and then tape that

 

Finally, the Jablite 70 would seem to suffice - is there any tangible benefit from upping the spec to the Jablite 100?

 

Regards

 

Tet

[Bitpipe]

The number that comes afte

Just now, Tetrarch said:

Finally, the Jablite 70 would seem to suffice - is there any tangible benefit from upping the spec to the Jablite 100?

 

That number refers to the compressive strength of the EPS - the point load in N per M2. When you put EPS as part of a foundation system then its very relevant and is specified by your SE.

 

The EPS under my basement slab is 200 grade.

 

Given you're using it on top, 70 is probably fine.

[Ian]

29 minutes ago, Tetrarch said:

 

Finally, the Jablite 70 would seem to suffice - is there any tangible benefit from upping the spec to the Jablite 100?

No benefit

I used 300mm of EPS 70 under our ground floor slab. It's been down 4 years with no issues. The slab was 100mm concrete with a D49 mesh with UFH

Edited March 2, 2021 by Ian

[epsilonGreedy]

This thread highlights the varying degrees of faith people have in the strength of concrete screed sitting on different thicknesses and different relative spongy behavior of insulation sheet types.