Floor slab insulation: PIR and EPS mix - what's on top? Separate with DPM?

[oranjeboom]

Okay, big iceberg delivery yesterday, so now I need to start laying the insulation for my slab:

 

 

Bungalow has two extensions which are piled slabs – both extension slabs will have a mix of PIR and EPS. The bungalow floor has been dug up, hardcore is down and I am ready to fill that with EPS.

 

The extension slabs both have SIPS sitting on blockwork, with cold-bridging around the sole plate best mitigated with marmox block beneath and external insulation on outside SIP wall (see pic). No feedback required on that please! : ) I just need a sanity check on the slab insulation please:

 

• Bamboo flooring
• 80mm meshed concrete with UFH (with 25mm EPS upstands)
• DPM
• 100mm PIR
• 160mm EPS
• Radon barrier (lapping with DPC under sole plate)
• 225mm Existing piled slab

 

 

A mix of PIR and EPS to attain desired u-value  / get correct FFL height. My thoughts were that it’s safest to get PIR on top of the EPS away from piled slab in terms of moisture. I was also thinking the PIR is better at withstanding point loads from the mesh chairs/spacers that will keep the mesh elevated above the insulation. Should I wrap it entirely in polythene/DPM to prevent moisture travelling up into the PIR? I was just going to cover the top with DPM as it is foil faced. Or should I have EPS on top and PIR at the bottom? Or does it matter??

 

Feedback appreciated.

 

OB

Edited May 5, 2017 by oranjeboom
EPS corrected to 160mm. doh

[Mr Punter]

I would have thought the radon barrier would be all the DPM you need.  Not sure what the others are for.  How are you fixing the sole plates?

[Dudda]

4 minutes ago, Mr Punter said:

I would have thought the radon barrier would be all the DPM you need.  Not sure what the others are for.  How are you fixing the sole plates?

The DPM is more a sheet of polythene to stop the screed or moisture from the screed making it's way down between the joints in the insulation when it's getting poured or having it dry out too fast particularly if it's getting polished.

 

I think the rule for walls, roofs, etc is to have the better insulation on the outside to prevent interstitial condensation. In a floor that won't matter so whichever is easiest. If you've underfloor heating I'd have the PIR on top as that's better and also if you use the plastic staples to hold the underfloor heating pipes down they'll get a better grip in the foil faced PIR than you would with EPS.

[A_L]

I am with Mr Punter on this, your radon barrier is also likely to be DPM. Certainly the one from Visqueen is http://www.visqueenbuilding.co.uk/products/gas-membranes/radon-membrane So another one not needed.

 

[MikeSharp01]

Yes provided the radon barrier does not get punctured by things, small stones / rough cement, sticking out of the slab then I cannot see the need for anything else. I cannot think why either way round has an advantage so either way and, as you saw with our pour the reinforcing supports didn't push through the EPS, in fact my experience was that he supports crushed before they went into the EPS.

 

 

[Onoff]

@oranjeboom, ref your question in the other thread:

 

25mm EPS in my case is to stop any sharp bits of the levelled, home made "Type 2" puncturing my DPM even though it's blinded with levelled sharp sand. Done after taking various advice on here. So to recap I went:

 

- Compacted "Type 2" direct to the clay

- Sharp sand blind

- 25mm EPS

- DPM

- 150mm PIR (100+50 overlapped at joints)

- Polypipe panels with Pex-Al-Pex UFH (this doubles to protect the PIR foil from the concrete)

- A142 mesh

100mm wet concrete (levelled with screeding rails on opposing walls).

 

Next time I wouldn't forget to add the fibres to the concrete!  The jury's out on the Polypipe panels. Makes it a doddle to run the UFH pipes and then some but it's not 100mm thick all over because of the 'castellations'.

 

I'd also likely lay the 50mm PIR first then the 100mm as the 50 is quite springy.

 

 

 

 

 

 

 

Edited May 5, 2017 by Onoff

[oranjeboom]

1 hour ago, Mr Punter said:

I would have thought the radon barrier would be all the DPM you need.  Not sure what the others are for.  How are you fixing the sole plates?

SIP structure is already up. Sole plates fixed through the marmox with bolt fixings into the blocks below (below the marmox blocks that is). 

The other DPMs - I was just going to use that to prevent contact with the cement on the foiled PIR - I have some spare, so may as well use it. Also a bit more durable than the poly when I am throwing mesh around on top. Potentially I was going to use DPM also to separate the PIR from EPS, but that appears unnecessary.

 

31 minutes ago, MikeSharp01 said:

Yes provided the radon barrier does not get punctured by things, small stones / rough cement, sticking out of the slab then I cannot see the need for anything else. I cannot think why either way round has an advantage so either way and, as you saw with our pour the reinforcing supports didn't push through the EPS, in fact my experience was that he supports crushed before they went into the EPS.

 

 

Slab all clean, clean from sharp bits also. Bit wet in places still so waiting for those areas to dry off before I cover with the radon/dpm.

When we poured the slab here, the chairs crushed all over the place with people walking all over the mesh to the point that the mesh ended up on the EPS. I ended up getting another bag of supports to elevate the mesh again before they came back for the pour. At least it's just me this time, so won't have to 'patch' things up after the experts have been in.

 

26 minutes ago, Onoff said:

@oranjeboom, ref your question in the other thread:

 

25mm EPS in my case is to stop any sharp bits of the levelled, home made "Type 2" puncturing my DPM even though it's blinded with levelled sharp sand. Done after taking various advice on here. So to recap I went:

 

- Compacted "Type 2" direct to the clay

- Sharp sand blind

- 25mm EPS

- DPM

- 150mm PIR (100+50 overlapped at joints)

- Polypipe panels with Pex-Al-Pex UFH (this doubles to protect the PIR foil from the concrete)

- A142 mesh

100mm wet concrete (levelled with screeding rails on opposing walls).

 

Next time I wouldn't forget to add the fibres to the concrete!  The jury's out on the Polypipe panels. Makes it a doddle to run the UFH pipes and then some but it's not 100mm thick all over because of the 'castellations'.

 

I'd also likely lay the 50mm PIR first then the 100mm as the 50 is quite springy.

 

 

 

 

 

 

 

Yes, I'll take a similar approach with the old bungalow set up, by laying 100mm EPS on the sharp sand and then radon barrier followed with remaining EPS insulation. Or I may just lay the radon barrier on top of the insulation to prevent ingress of concrete between any EPS joins. Decisions!

[oranjeboom]

One further question: I presume it's best to continue the radon barrier up the inside wall then lap it underneath the DPC? as I have shown in the above pic and made clearer here:

 

 

I'll use doubled sided tape underneath and then finish off with jointing tape on top. 

 

 

TIA! 

 

Edited May 5, 2017 by oranjeboom

[MikeSharp01]

I would take the radon barrier out beyond the block and drop it down so as to be sure that you get coverage. As you ahve drawn it damp rising in the block work could migrate along the bottom of the DPC over the radon barrier and into the concrete / insulation, if you get over the blocks with the radon this cannot happen all rising damp stops dead there.

[oranjeboom]

31 minutes ago, MikeSharp01 said:

I would take the radon barrier out beyond the block and drop it down so as to be sure that you get coverage. As you ahve drawn it damp rising in the block work could migrate along the bottom of the DPC over the radon barrier and into the concrete / insulation, if you get over the blocks with the radon this cannot happen all rising damp stops dead there.

 

Yes ideally that would have been the way to go. But the SIPs are already up you see. Working front to back here! Blockwork does have DPC at the bottom though (between slab and blockwork), so little transference of damp at that point. The ground level outside will be lower than that DPC (ignore first pic) also so won't have a case of soil moisture being transferred to the blocks. Blocks will be shielded by exterior EPS and final covering of brick slips. So I hope I am covered on the rising damp front.

 

Alternatively, I could lap the radon over the DPC rather than underneath, but more potential for ingres of radon/gases. Not that I am in a high risk area. Previous occupants in bungalow did not die of radon either.

[MikeSharp01]

Cripes - you are only down the road from me and I thought that radon was a rock strata issue not a clay base issue had not even contemplated that I might need to keep radon out.

[oranjeboom]

Yeah, that's what I thought too. There's an online map you can check, and from memory along the coast where you are there no radon risks.