UFH set-up

[stepheni]

I am soon to be laying my underfloor heating in my extension but have a couple of queries. 

 

• Is it ok to use non-foil PIR insulation under the screed?  I am sure I read on the celotex website that the foil was only necessary if there was an air gap behind the insulation.  This would then be covered in polythene before pouring the screed
• See from picture that I have 75mm left from top of insulation.  Was planning on a traditional sand/cement screed (65-70mm) then leaving 5-10mm for vinyl flooring (karndean or similar).  Would this be ok or should I look at liquid screed?
• What do you do round the perimeter for UFH for insulation?  Also if you see in the photo at the bottom of the doors there is a ridge how do you deal with this for the perimeter insulation

[Nickfromwales]

Perimeter insulation can be 25mm kingspan / other rigid insulation, but for a thin dry screed you'll need to have some other form of expansion skirting ( applied directly in front of the 25mm upstand ). 

Sonething like this is what I use. Shop around for best price . 

Liquid screed has a lot of 'after lay' preparation and mechanical cleaning that's needs doing to it before ANYTHING will stick to it ( including primers ). I'd stick with the dry screed TBH, but there are liquid screeds of varying performance based on how much you want to spend. 

With a <70mm dry screed you need to ensure that you observe expansion gaps at the door thresholds so talk to both the screed layer and Ufh installer accordingly about fitting some of these type of things. 

[stepheni]

Cheers nick got it.

 

Anyone got an answer on the first question on whether it is ok to use the non foil boards? 

[Jeremy Harris]

The foil would only get corroded by concrete, anyway, so there seems no point in having it if it's in contact with anything with cement in.