After asking around, this is all I can find on decoupling in British Standards;
From BS5385-3:2014 clause 5.5
Polyethylene or suitable sheet membrane should be used in preference to
building paper or bituminous felt. A minimum thickness of 0.125 mm should be
used for most conditions, the purpose of the separating layer being to ensure
that the applied screed or concrete does not adhere to the base.
NOTE Uncoupling membrane systems provide an intermediate substrate between
the tile covering and load bearing substrate. They can be used over a variety of
substrates, which include timber, concrete, cementitious screeds and gypsum based
screeds, etc. They are designed to neutralize lateral stresses that occur between the
substrate and tile covering; they are not designed to accommodate differential
vertical movement. The membrane works by preventing stresses from the substrate
being transferred into the tile covering; this prevents cracking and possibly
delamination of the covering material. They are designed to work with tile adhesives
where the bedding does not generally exceed 10 mm.
It doesn't mention heated screeds or even recommend anything. Is there a bit on this subject I've not found?
