UFH Pipes on to concrete slabs

[Conor]

Hi,

 

We've just got our ground floor slabs in and have realised the FFL is going to be too high with the planned build up - 25mm PIR, UFH pipes, 75mm screed. (too high as in we're overlooking neighbours as it is)

 

As its a passive house, heating wont be on very often and only have a small area heated, so not bothered about heat from UFH loops going in to the slabs. This would mean we could get away with about 40mm liquid screed, rather than the proposed 100mm build up.

 

Would it be a complete pain nailing/screwing UFH clips to the precast slabs? Any other issues?

Edited November 13, 2020 by Conor

[Declan52]

You could use a mat type system.

https://underfloorheating-direct.com/polypipe-1200mm-x-1000mm-floor-panel-31512-p.asp

[Onoff]

Get a man in and route slots in the concrete?

 

 

[markc]

If the slab is still green then cutting channels is messy but not too difficult.

Nailing clips to the slab with a nail gun isnt difficult ... easier than cutting channels

[A_L]

38 minutes ago, Conor said:

Would it be a complete pain nailing/screwing UFH clips to the precast slabs? Any other issues?

 

you can fix UFH pipe to clip/mount rails which use adhesive patches to fix.

 

https://underfloorparts.co.uk/product/underfloor-heating-clip-rail-track-1mtr-adhesive

 

but would less than 25mm cover above pipe be O.K. 1)mechanically? and 2)heat spreading?

[joth]

3 hours ago, Conor said:

We've just got our ground floor slabs in and have realised the FFL is going to be too high with the planned build up - 25mm PIR, UFH pipes, 75mm screed. (too high as in we're overlooking neighbours as it is)

 

What purpose is the 25mm PIR serving?  In my uneducated mind, it's way too thin to have any value and if you're building a passive house the concrete slab is obviously already very well insulated so why insulate it again?

 

[Conor]

10 minutes ago, joth said:

What purpose is the 25mm PIR serving?  In my uneducated mind, it's way too thin to have any value and if you're building a passive house the concrete slab is obviously already very well insulated so why insulate it again?

 

We've a basement underneath. This is essentially and intermediate floor. Only purpose of insulation is to prevent heat from UFH sinking in to the slab. My original point is that as heating will be so rarely used, I can live with this effect. 

[Nickfromwales]

58 minutes ago, Conor said:

We've a basement underneath. This is essentially and intermediate floor. Only purpose of insulation is to prevent heat from UFH sinking in to the slab. My original point is that as heating will be so rarely used, I can live with this effect. 

Agree that 25mm will only be of benefit to affix the pipes with pipe staples. I’d bin the 25mm insulation and just use clip rails direct onto the slab, fixed down with a Spit nailer. Then sand and cement ( dry ) screed at 50mm thick. 

[Conor]

Update on this... both my architect and builder think this is a stupid idea.... so back to  sheet of insulation, UFH and then liquid screed.

[Bitpipe]

Obviously too late for you but this was one of the reasons we went with suspended timber floor over the basement ('open box' construction). Basement slab sits on 300mm EPS with 200mm applied to outside & meets the insulated layer in the twin wall TF above.

 

We skipped any UFH (or any heating) in basement and it's always sitting at 20^oC or thereabouts.

 

Put alu spreader plates on GF joists, pipe and then the 18mm OSB deck on that, leaving out a strip of OSB where the pipes hopped over the joists at each end.

 

Added 9+12mm cross laid ply to that as sub-base for resin floor (which sits on 6mm rubber crumb mat) so the whole build up is about 50mm thick.

 

Works fine, floor is soft and warm underfoot when needed - as we're PH standard, heating is rarely on.

 

I was worried that if we heated the top of a concrete box, we'd end up heating the whole structure over time.

 

I don't think we saved any money in forgoing the top of the basement box as the walls needed to be thicker and stronger as a result (300mm vs 200mm) so probably the same amount of steel and concrete plus the cost of a steel web over the floor and joists.