"Glueing" PIR insulations board to concrete.

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Hi.

Is there a best way to "Glue" PIR to a concrete floor. I have an existing screed of 70mm that I am replacing with 20mm PIR and 50mm flowing screed, just wanted to make the boards a little more secure while installing UFH pipes, etc.

My plan was for a few blobs of spray foam with a few heavy blocks on top of the board while it goes off, that stuff seems to stick to everything, even the stuff you don't want it to stick to!

Cheers.

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20mm of pir won't satisfy building regs.
Are you sure you want to proceed with this as you'll be loosing a lot of heat from your underfloor heating.
 
20mm of PIR is not very much.
You could use VIPs, if you have enough budget. (20mm VIPs cost about £100 / sqm; to get the same level of insulation using PIR you'd need about 80mm, costing about £15 / sqm.)
If you can't afford that and really want to continue, make sure your boards are phenolic, i.e. Kooltherm, not just PIR. That gets you about another 20% I think.
 
Agreed with the above you'll need more like 80 to 90mm boards, but to answer your questions if you tape it together andand dpm on top that should help stop it floating away
 
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Thanks all. The 20mm is being retrofitted into the existing kitchen diner. The actual extension has 120mm insulation. The 20mm was the max I could get given the existing screed depth. Do building regs have to be taken into account for the existing but if the house? 20mm is better then the zero that was there before. Thanks again.
 
Apply a brick stabiliser to the concrete floor, then use adhesive foam such as everbuild or illbruck
 
20mm is better then the zero that was there before.
Did you have ufh before though? Heat loss through floors is actually quite low due to heat rising. However make the floor your radiator (a massive surface area) and the back half is going into the floor.
Heat loss is based on temperature difference, and with ufh it can be three times the difference as without the ufh. Also ufh covers the whole floor, much bigger than a rad, and usually has some kind of floor covering meaning slightly less heat coming upwards.
All in all your insulation is more critical for ufh.
 
Do building regs have to be taken into account for the existing but if the house? 20mm is better then the zero that was there before.

Some regs have a "no worse than previously" rule for upgrades to existing structures; I'm honestly not sure if this applies in your situation. Have you submitted plans and had them approved?

How much of the perimeter of this area is external walls? If not much, that also helps.
 
And as you're putting UFH in, you're going to insulate the perimeter of the slab as well. Now I could be wrong, but I was under the impression that you could get away with a 40mm slab if it was a flowing screed.
 
There is a build thread here that will hopefully answer some of the questions.

https://www.diynot.com/diy/threads/maybe-if-we-just-knock-that-wall-down.487243/

The flowing screed will be between 40mm and 50mm. Existing house isn't that level :(

Building regs plans were submitted and approved for the extension. The perimeter will be insulated. Only 1 wall will be external, about 4.8m.

No UFH heating beforehand.

Cheers
 

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