75mm uptstand insulation, ok or not?

[grahamA]

Any one see any issues with instaling 75mm PIR insulation as an upstand in terms of its ability to support a finished floor on top? This will be only in areas where we are continuing the floor build up to the outer leaf (bi-fold door opening). Other areas will be a 25mm upstand. 

 

Floor insulation will be 150mm and slab 150mm. Plan for above the the slab will be 5-10mm self leveling compound (marrying upto exisitng floor), 20mm underfloor heating panels and then 22mm floor tile.  

[JohnMo]

I used 70mm.  The only real place mine was exposed was at doorways. Due to strapping the walls out 50mm, plasterboard and skirting.

 

Tiler was a bit surprised, but used a very flexible tile adhesive, we have thick commercial tiles, no issues a year later. The carpet fitter didn't even comment, but I did use a self leveling screed at those doorways.  Again no issues.

 

[Nickfromwales]

1 hour ago, grahamA said:

Any one see any issues with instaling 75mm PIR insulation as an upstand in terms of its ability to support a finished floor on top? This will be only in areas where we are continuing the floor build up to the outer leaf (bi-fold door opening). Other areas will be a 25mm upstand. 

 

Floor insulation will be 150mm and slab 150mm. Plan for above the the slab will be 5-10mm self leveling compound (marrying upto exisitng floor), 20mm underfloor heating panels and then 22mm floor tile.  

Why aren’t you putting the pipes in the slab? Add 50mm more insulation ( EPS ) and reduce concrete. Lose the UFH panels and save some money. You’ll end up heating the slab regardless, so will have slow reaction times to shift room temp, so why this choice of floor arrangement? 

[grahamA]

The main reason is that its going to be an open plan area joining into an exisitng slab which isn't insulated but which i want to install underfloor heating on without adding too much floor height. UFH panels across the whole floor was what i cam up with to ensure i get an even floor across the two floors. When you say 50mm eps, would that sit on top of the slab, where you would then install the UFH heating pipework in screed above?? Not sure if i'll be able to do that as the builder is planning to tamper the concrete off of the blockwork which is already at the intended height.

 

Any thoughts on my initial question?  

[grahamA]

2 hours ago, JohnMo said:

I used 70mm.  The only real place mine was exposed was at doorways. Due to strapping the walls out 50mm, plasterboard and skirting.

 

Tiler was a bit surprised, but used a very flexible tile adhesive, we have thick commercial tiles, no issues a year later. The carpet fitter didn't even comment, but I did use a self leveling screed at those doorways.  Again no issues.

 

Thanks John. Good to know.

[JohnMo]

To have the same UFH across two different floor buildups could work badly, as they may or very likely require different flow temperatures to counteract the differing downward heat losses.

 

If you are doing this, you want to think about different manifolds for the different floors, the flow temp for the new floor could be in the high 20s to high 30s, depending on the overall heat loss.  The old floor flow could be in the mid to high 40s, and still not heat the room well.

 

I would do as Nick suggests, and I really would not want UFH in an uninsulated floor.  It will be a money pit for running costs, perform badly and generally disappoint.

[Conor]

Don't even consider putting UFH on an uninsulated slab. Do as nick says, and forget about UFH in the old part. Put a couple rads in.

[Nickfromwales]

Yup. UFH is done badly more often than it’s done well, particularly when a general builder just comes up with a ‘good idea’. 
Look at the overlay system from Wunda, that may be your best option. 
If it was my house I would break out the existing floor and do it properly, as retro fit UFH done anything less than immaculately will likely not heat the room unless left on pretty much 24/7 with massive running costs to boot.

Original question; yes no issues there. You can cut the up-stand back by 20mm if you’re worried, and bond a strip of Compacfoam ( 400kpa ) on top just where there’s going to be traffic etc.