Floor insualtion - how precise do I need to be?

[Conor]

Just started laying the 200mm floor insualtion on our basement, small room as an experiment. Build up is tanked concrete slab, 50mm EPS, 50mm PIR, 100mm PIR, DPM, UFH, 50mm liquid screed.

 

Ive scraped off any lumps on the floor and done a quick brush up. I'm laying the boards staggered and as tight as possible. It's not perfectly flat but within 15mm across the slab.

 

What sort of gaps are acceptable at joins? 5mm Ok? Expanding foam for anything bigger.

 

What about vertical differences at joins? I've a couple boards that don't line up and there is a few mm (5mm or so) and when you stand on the edges they settle down. No rocking as such. Is this acceptable? I'm assuming weight of the screed with deal with this.

 

Is taping required? And presume just the top layer? 

 

And, yes, I 100% agree that cutting PIR is the most horrible job in a house build.

 

Edited January 12, 2022 by Conor

[markc]

Wedge boards as tightly together as possible, foam any gap that won’t close up.

small differences in level at joints is normal and these will squash down and everything settles with some load on.

tape every joint if you can, costs very little and is worth it for piece of mind.

Edited January 12, 2022 by markc

[MikeGrahamT21]

Yes, tape the joints with aluminium tape (top layer only is fine), foam any larger gaps, and smaller ones too if the nozzle will go in.

 

You basically need to be able to pour what is the consistency of double cream on and it not go down the cracks, otherwise you are in the realm of thermal bridging, with there being more than one layer, if it gets under it could float the top layer slightly too, would be a shame after all the work.

 

Don't worry about slight unevenness, as long as the joints are taped, everything will settle one the screed is poured

Edited January 12, 2022 by MikeGrahamT21

[nod]

Yes tape the joints 

Any lumps or. Bumps will soon be flattened by the weight of the screed 

 

[Conor]

Should I tape between the boards and wall?

[joth]

On 12/01/2022 at 15:54, MikeGrahamT21 said:

Yes, tape the joints with aluminium tape (top layer only is fine), foam any larger gaps, and smaller ones too if the nozzle will go in.

 

You basically need to be able to pour what is the consistency of double cream on and it not go down the cracks, otherwise you are in the realm of thermal bridging, with there being more than one layer, if it gets under it could float the top layer slightly too, would be a shame after all the work.

 

Don't worry about slight unevenness, as long as the joints are taped, everything will settle one the screed is poured

Presumably the DPM will ensure nothing can get into / under the PIR+EPS sandwich?

 

We had DPM under the insulation so taping was a lot more mission critical.

 

55 minutes ago, Conor said:

Should I tape between the boards and wall?

Again DPM should mean it's not necessary, but you might want to anyway just to help pin everything in place?

I doubt the aluminium tape will hold on the block work/concrete though unles you cover it with sprayon primer first? Feels like a job for heavier tape. 

 

[joth]

58 minutes ago, Conor said:

Should I tape between the boards and wall?

Actually now I think about it we put in a 75mm high PIR upstand around the perimeter to keep the screed  off the walls. The upstand was actually all put in first so the horizontal boards propped it up

[MikeGrahamT21]

Yes you need an upstand, 25mm all way round, which would normally be tucked into the floor insulation to keep it in place, which allows for any expansion of the concrete without cracking.

 

Bead of silicone all way round the junction to stop leakage, then put an upstand in, which can be cut to correct size once pour complete and set.

[Conor]

3 hours ago, MikeGrahamT21 said:

Yes you need an upstand, 25mm all way round, which would normally be tucked into the floor insulation to keep it in place, which allows for any expansion of the concrete without cracking.

 

Bead of silicone all way round the junction to stop leakage, then put an upstand in, which can be cut to correct size once pour complete and set.

 

The guy from the screed company is here today laying the polythene and taping a 25x100mm expansion strip around all the walls.

[Thorfun]

Just now, Conor said:

 

The guy from the screed company is here today laying the polythene and taping a 25x100mm expansion strip around all the walls.

been through these discussions on this thread recently

 

 

common consensus seems to be that 8mm expansion strip is all that's needed and it is what our screed company has asked for (just bought 125m of the 8mm x 150mm stuff from eBay). I thought the 25mm or thicker insulation upstand was to reduce thermal bridges? but you've got ICF, right? so there shouldn't be any of those. @Nickfromwales has also mentioned in the past (iirc) that even with the insulation upstand you'd still need the expansion strip.

 

I do have a thousand things going around in my head though and so can't retain everything I read so I might be wrong. plus I'd hope the screed company know what they're doing!

[Conor]

I'm now thinking it's not 25mm... Could be thinner. I could check but Im enjoying my hot soup right now.

[Nickfromwales]

If it’s doesn’t compress, fit the foam expansion skirting afaic. It’s an expensive mistake if you find it was needed.