On 26/01/2021 15:07, Tim Lamb wrote:
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?
Â*One difficultyÂ* we discovered with a refurb and planned underfloor
heating throughout is adequate insulation over solid floor slab.
Â*The original arrangement with wall hung radiators had 25mm
polystyreneÂ* under 22mm chipboard. The new system uses slotted
polystyrene slabs withÂ* about... 25mm of insulation below the pipes!
Â*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.

Building Regs Part L used to have tables of Uvalues or heatloss
associated with the perimeter. If you only insulate a 1 metre band
around the edge (inside) that is most of the downward heatloss fixed.

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.

Sarah Beaney built a new mansion in Somerset (recent TV series)
and the inner edge of the foundation trenches were lined with
what looked like the blue extruded polystyrene that is ?normally
used under the slabs of coldrooms, and then the concrete poured.