Taping the outside edge of PIR?

[Tony K]

I'm about to lay PIR boards on top of my concrete slab (inside the watertight superstructure) ahead of a dpm, UFH and screed. I will be laying the boards in a staggered pattern and taping over the joints with the appropriate silver tape. 

 

A neighbour has recommended the application of a different but similar tape to the exposed outside edge/face of the boards, covering the polystyrene faces that meet the internal walls. He says this increases performance. 

 

Anyone heard of this? 

Edited March 8, 2023 by Tony K

[ADLIan]

No. Waste of time and tape

[Bonner]

+1 waste of time, the edges should be butted up to an upstand anyway

9 hours ago, Tony K said:

covering the polystyrene faces that meet the internal walls. He says this increases performance. 

 

[JohnMo]

11 hours ago, Tony K said:

lay PIR boards on top of my concrete slab (inside the watertight superstructure) ahead of a dpm, UFH and screed

Your DPM should be below you concrete slab.  The is no DPM above the PIR, that's just a seperation layer to stop the concrete in the screed making contact with the aluminium foil and causing a chemical reaction.

 

As mentioned your boards should be butting up against and insulation upstand.

[Dave Jones]

the upstand actually can sit on top of the boards, a lot of ufh installers use the sticky stuff which is really thin.

 

Use Marmox blocks as the first course and you dont have to bother with any upstand. They are a better U value than the insulation and stops the internal walls becoming a massive radiator leeching heat from the floor.

 

https://www.marmoxonline.co.uk/en/thermoblock/160-marmox-thermoblock.html

 

 

[Iceverge]

Technically he may be right. One of the reasons I prefer EPS. I'm not sure if the products have improved since this test but it shows with no facer the insulation degrades faster.

 

https://www.researchgate.net/publication/44073583_Long-term_thermal_resistance_of_Polyisocyanurate_foam_insulation_with_impermeable_facers

 

 

[ADLIan]

18 minutes ago, Iceverge said:

Technically he may be right. One of the reasons I prefer EPS. I'm not sure if the products have improved since this test but it shows with no facer the insulation degrades faster.

 

https://www.researchgate.net/publication/44073583_Long-term_thermal_resistance_of_Polyisocyanurate_foam_insulation_with_impermeable_facers

 

 

 

Most of the blowing agent loss, hence loss in thermal performance, is through the top and bottom faces and is accounted for in the declared lambda value. The foil facings slow this process hence foil faced PUR has a lower lambda than product with glass tissue or bituminous facings. Edge losses are minimal. The foil-facing is a complex laminate of al foil, kraft paper and polyethylene and is adhered to the uncured, liquid foam in the manufacturing process. Adding a self adhesive foil tape to the edges would not be gas tight and would make no difference.

[Iceverge]

1 hour ago, ADLIan said:

Edge losses are minimal.

 

Any more info on the edge leakage for further reading? 

 

 

[Tony K]

5 hours ago, Bonner said:

+1 waste of time, the edges should be butted up to an upstand anyway

 

 

I have been thinking about upstands.

 

My original detail was as follows:

 

 

Following minor water ingress (the bituthene layer plainly having failed somewhere), I had a basement/waterproofing firm instal an internal drainage system, akin to those used in basements. They have applied 8mm waterproofing membrane to the wall, 50mm waterproof insulation across the top of the slab, and an 8mm membrane across the top of that, taped into position, including around the edges. 

 

I plan to lay a further layer of 50mm PIR on top. I will then add a DPM (not to prevent damp, but as @JohnMo rightly says,  its just a separation layer to stop the concrete in the screed making contact with the aluminium foil and causing a chemical reaction. The UFH pipes will go on top, then 50mm of screed. 

 

I will place a 5/10mm expansion foam around the perimeter in all rooms using tape to secure it to polythene, as shown here:

 

 

Can/should I still try to incorporate a PIR upstand in these circumstances?

 

Thanks

Edited March 9, 2023 by Tony K

[Mr Punter]

Yes.  Even more so if the lowest inner leaf block is not aircrete, as you will have a thermal bridge via the slab.

[Tony K]

29 minutes ago, Mr Punter said:

Yes.  Even more so if the lowest inner leaf block is not aircrete, as you will have a thermal bridge via the slab.

 

And would I instal the PIR upstand so that the top of it is level with the top of the screed, and then tape up and over that upstand to the wall?

 

Or, is there any value in installing an upstand to the edge of the PIR which is the same height as the main body of PIR (i.e 50mm) but which is, at least, positioned so that the foil face of the board is adjacent to the wall?

Edited March 9, 2023 by Tony K

[ADLIan]

5 hours ago, Iceverge said:

 

Any more info on the edge leakage for further reading? 

 

 

Sorry no - been a few years since I worked in that sector. From memory BS EN 13165 on PUR manufacture gives info on gas tight and non-gas tight facings and their effect on thermal performance. Gas transfer into/out of the foam matrix at the edges has little impact on aged lambda.

[Tony K]

I have now seen the standard perimeter insulation upstand details (25mm PIR) on this:

 

https://www.labc.co.uk/news/how-to-get-it-right-perimeter-insulation

 

The firm who designed and supplied my UFH kit have also given me rolls of the blue foam stuff shown in my earlier image.

 

https://www.bes.co.uk/edge-insulation-16882/

 

They say it will act as a thermal break between the edge of the screed and the wall, and that a PIR upstand is not necessary therefore. In fairness, they did say the blue foam was not as good as PIR, only that it broke the cold bridge.

 

Would any of you be happy with this foam instead of PIR?

Edited March 10, 2023 by Tony K

[Iceverge]

Assuming a cavity wall with strip foundations that perimeter strip has a noticeable effect on the thermal performance of the wall floor junction. 

 

Thermally I'd put as wide a strip of PIR in there as I could fit with the caveat that too wide and fitting carpets will be a pain. 

[JohnMo]

1 hour ago, Iceverge said:

Thermally I'd put as wide a strip of PIR in there

That's what we did, 70mm around the whole perimeter. The walls were ok, as they got battened out 50mm plus plasterboard.  The doorways were a bit of a pain.  But everyone coped and got the floor finish completed.

[Tony K]

14 minutes ago, JohnMo said:

That's what we did, 70mm around the whole perimeter. The walls were ok, as they got battened out 50mm plus plasterboard.  The doorways were a bit of a pain.  But everyone coped and got the floor finish completed.

 

I will have 25mm batons with the plasterboard mounted, and so can quite easily accommodate at least 25mm PIR upstand (which seems to the be depth shown in most standard details).

 

My concern is more about whether I am wasting my time in adding the PIR upstand, as I am already adding the blue foam?

[JohnMo]

The way I looked at, is 10mm of the blue foam is best to no insulation, there to soak up some expansion really.

 

PIR much better insulation value, you don't need much to go around the house.  Our were but 300mm strips, so 4 strips out of a board, so 10m almost length from 1 board.

 

You could put 40mm in there very easy.  25 + 12.5, would only strick past the plasterboard 2.5mm.

[Tony K]

1 hour ago, JohnMo said:

The way I looked at, is 10mm of the blue foam is best to no insulation, there to soak up some expansion really.

 

PIR much better insulation value, you don't need much to go around the house.  Our were but 300mm strips, so 4 strips out of a board, so 10m almost length from 1 board.

 

You could put 40mm in there very easy.  25 + 12.5, would only strick past the plasterboard 2.5mm.

 

I am thinking of....

 

1. Installing the PIR boards out across the floor. Tape the joins.

2. Add 25mm PIR upstands to the edges.

3. Add the visqueen/DPM (just to keep the screed off of the PIR).

4. Use the blue foam around the edges.

5. Screed.

 

That should do it?

 

[Iceverge]

Consider how best to jamb the PIR upstands in place. You can put them in place first and then wedge them with the floor boards or stick them later with some expanding foam . 

 

I think I prefer the former. 

 

I would go for more than 25mm if I could. It's just a bit fragile at that depth. Wouldn't bother with the blue foam TBH. Just more PIR.