Proposed floor build up over UFH

[Captain Scally]

Hi,

I am trying to achieve a low floor build up including wet UFH over a new suspended timber floor in our barn conversion. The area is large, 21m x 8m. Having spoken to various UFH suppliers I have come up with the following:

1. 22mm chipboard subfloor (already laid)
2. 25x25mm battens at 200mm centres
3. 16mm PEX pipe UFH nail clipped to the sub floor
4. 8:1 PUG mix dry sand & cement packed around UFH pipes
5. 6mm No More Ply
6. Flexible tile Adhesive
7. 15mm Natural limestone floor tiles

I am planning to us expansion joints at 5m intervals. I have been told that I do not need a decoupling membrane with the No More Ply.

My target is to keep the overall build up excluding the chipboard subfloor to less than 50mm. I have investigated overlay panels but the seem to be a very expensive option and I am told that they do not perform as well as the PUG mix. I appreciate that what I proposing is a lot of work.

Please can I have your views, good or bad.

Many thanks, Captain Scally

 

[Ajax123]

Why not use liquid screed rather than "pug" mix. It'll improve the thermal performance of tye heating enormously.

 

[Captain Scally]

Thanks for that Ajax. I seem to be getting conflicting advice - I was told the the PUG mix was best for heat transmission but I can see that a liquid screen would have better contact with the pipe.

Is the liquid screed suitable for such a thin covering over the pipe?

 

[Ajax123]

In terms of thermal performance a pug mix is probably the worst performer of all of them. If you needed the screed to act as a sub base to receive the tiles you would need 20mm cover over the top of the pipes. In the arrangement you are proposing you don't need it to do that, you are simply after a conductive thermal mass. Gypsol anhydrite liquid screed will do that perfectly. You dont need cover go pipes to do that job. If it cracks a bit...so what. Its how i did my last loft conversion floorcabout 7 years ago. The board on top is doing the sub base work. I'd probably consider using a gypsum floor board as well but these tend to be 18mm deep so you might not have space.