Retrofitting DPM for UFH

[Jilly]

Still struggling with how to retrofit the DPM (on rough old solid concrete floor) and insulation etc Am not going to manage brilliant insulation as I failed to realise we couldn't take the DPM above the DPC ( at 150mm), even tho there is the head height. 

Am hoping for UFH in screed (supplied won't do 50mm, only 65mm). Would the retrofit UFH sort which goes over a floating floor be better? 

 

See BC full plans specification: there is a significant thermal bridge, so I would like to use Kingspan Kooltherm K103 as it has a better u value than Celotex PIR and also use it as an upstand. Does it have to overlap the DPC too (as the extern al wall insulation doesn't come down far enough)?

 

Have been told to use sand blinding layer, but how should we protect the DPM from the rough wall bits, is a combination of 'paint on' OK?

 

Would really love a Noddy's guide on how to do this ? Or at least which rules I need to follow...Thank you everyone

 

 

Floor detail.pdf

[PeterW]

1 hour ago, Jilly said:

Am not going to manage brilliant insulation as I failed to realise we couldn't take the DPM above the DPC ( at 150mm), even tho there is the head height. 

Says who..??

 

Sand blinding over the concrete then build an insulation upstand. 

[Temp]

Either a sand blind or possibly some 25mm EPS would protect the DPM. Could fit some perimeter insulation (blue roll) to protect it if the walls are very rough.

 

How much height do you have and what floor coverings do you need to allow for?

 

 

[Jilly]

When I asked, BC said that you wouldn't normally go above the DPC and wanted me to submit more architects drawings. The architect's technician thinks I could get away with asking them at an inspection (a different BC officer attends). 

 

The floor varies, the DPC is 150mm to the second course of bricks and the wooden batten is placed at 250mm at the bottom near the patio door (which I was hoping to make into a low profile entrance), but it is less in other places (see other photo). The slate tiles I have bought are 10mm. 

[Temp]

I can't think of any problems that would arise if the finished floor level was above DPC..... after all the first floor is 3m above DPC ?

 

 

[Temp]

Disabled access ramp to front door wouod have to be a bit higher? 

[Temp]

OK so you have..

 

150mm

-10mm slate

-5mm adhesive (more if stone is bit irregular?)

= 135mm

 

-65mm screed

=70mm available for insulation, DPM and blind.

 

I'm thinking a 20mm closed cell insulation, DPM and 50mm PIR.

 

Not ideal though. We have around 80mm of PIR insulation under our UFH and would definitly put in more if building again. I'd probably aim for at least 150mm.

 

If you really don't want to raise the door sill there are some UFH boards that can be tiled over without screed. They are typically 20mm thick and intended to go on top of suspended timber floors but it might be possible to adapt them for use over insulation or insulation and OSB. No screed required. One issue is that insulation boards don't always lay flat and need screed to weight them down so the don't move under load causing cracks in tiles/stone flooring.

 

 

https://ambienteufh.co.uk/tiling-over-underfloor-heating/

 

https://www.wundatrade.co.uk/shop/home/quick-shop/wundatherm-quick-shop/boards-quickshop/underfloor-heating-board-wundatherm-ultimate/

 

Who is your UFH vendor?

 

 

Edited July 28, 2021 by Temp

[Jilly]

As I understand it the DPM should ideally be contiguous with the DPC...

 

Lithotherm tiles (recycled brick) for UFH are heavy only 45mm thick and a screed replacement, but I don't know anyone who has used them.

Edited July 29, 2021 by Jilly