Engineered flooring

I would have said floating was better given the heating cycles as long as the floor is on an underlay that aids sliding.

I have heard of bonding it down, but no personal experience - all mine are floating.

I disagree that glued joints are likely to fail if done well - I have seen "clicky" laminate work some tiny gaps before over a year but my clicky engineered floors have been fine over quite moderate temperature cycling - and one of those is heavily weighted down with wardrobes and shelves which does occasionally cause a very slight creak as you walk over it but is seems to handle expansion and contraction OK generally.

If you go to UK Self Build faq there is a significant section on UFH and engineered flooring. (I wrote it)

I laid engineered Oak and very pleased with the product.

Your basic idea is correct ... use a 2/3mm closed cell underlay that has good heat transmission properties (not insulating) .... lay floating, and glue joints with quality PVA. Good tip is to fix in 3 or 4 strips first and, making sure it's fully scribed in and 2 & 3rd rows are absolutely square, clamp up with ratchet clamps and leave overnight.

Space off wall by 10mm spacers and then fit rest ... I would advise no more than about 1.2m depth each time before allowing glue to set.

Do NOT glue to screed... it will not suit UFH ...

I have had my Oak flooring down for 7 years .... no joints have opened, sprung or warped .... that is the beauty of engineered flooring it is dimensionally stable. Also if I ever want to re-finish it will re-sand at least 3 times.

Happy to take any questions by PM ... as I don't read group every day.

p.s. If you want a cheap set of ratchet clamps let me know ... finished with mine.