In message , Andrew
writes
On 26/01/2021 08:57, Tim Lamb wrote:
In message , Andy Burns
writes
ARW wrote:

OK so this is a refurb and not a newbuild I am working on.

Is the whole thing anywhere near done yet?
One difficulty* we discovered with a refurb and planned underfloor
heating throughout is adequate insulation over solid floor slab.
The original arrangement with wall hung radiators had 25mm
polystyrene under 22mm chipboard. The new system uses slotted
polystyrene slabs with about... 25mm of insulation below the pipes!
We could have put more under but only by losing ceiling/door height.


Don't worry. According to the ?polyplumb salesman at a
self-build exhibition that I visited many years ago, he
assured me that even though the overlay slotted
insulation panels were only an inch thick, it would
still be cheap to run because 'heat rises'.

Ha! I suspect I am warming a lot of Hertfordshire. I think TNP suggested
the main loss is to the sides rather than directly down.

It has crossed my mind to consider external insulation down to the
footings. Currently shingle filled French drain so not a huge job but
without some idea of the benefit, not over likely to happen.

--
Tim Lamb