Be aware that if the manufacturer says sand & cement base and the tray cracks when its down, they usually ask for photo before sending a replacement for just this reason.
Horizontal battens fixed with adjustable screws is another option. They are ingenious things, usually used for fixing battens to wonky timbers but you could use them to back out the battens to the depth of the straps. Widely used on the continent but not seen them used much here.
https://www.amazon.co.uk/TOX-Adjusting-Distance-100-Pieces-09010102/dp/B0166R6KCW/ref=pd_day0_sccl_2_5/259-0917683-5637240?pd_rd_w=7SQ7e&pf_rd_p=8ec13b8a-30d2-48fc-8503-84c56766370d&pf_rd_r=RX8059BTWHP0K1GWJ34H&pd_rd_r=1ce504d0-870b-4d7e-a1a2-ce3c93bd680b&pd_rd_wg=PEOJl&pd_rd_i=B0166R6KCW&psc=1
Just finished mine, low profile shower tray sealed with abacus no more leaks tape.
Multipanel on the walls and i didnt use the multipanel seal kit following recommendations here, I wouldnt go back to tiles.
Silicon (UniBond Triple Protection) also finished with Cramer tool, nice pro finish but still a bugger getting a nice 3 way corner to look good.
A habitable room is defined as ‘…a room used for dwelling purposes but which is not solely a kitchen, utility room, bathroom, cellar or sanitary accommodation.’
Take a look at the Fire Safety Building Regulations. Page 15 onwards
Apparently the latest thing is microcement finished worktops which are touted as hardwearing, joint free & crack resistant and come in pretty much any colour and finish, looked quite good from what i saw, came in around £100-150 m2 just for the finish (usually applied to mdf or ply tops), can even DIY.
One question. Did you also install a land drain? or not bother? and for what reasons either way.
They always seemed to be spec'd on the raft designs i've seen but dont actually seem to be that often installed looking at the examples on this site?
Thanks
The 'Future Homes Standard' is currently under consultation see https://www.gov.uk/government/consultations/the-future-homes-standard-changes-to-part-l-and-part-f-of-the-building-regulations-for-new-dwellings although a lot of people dont think it goes far enough, see https://www.leti.london/part-l for one of the many well thought responses.