When i pulled a concrete slab driveway up one time there was an existing clay pipe below it. Was fine. Bet that was less than 200mm. Concrete had mesh in was tough as nails.
See lots of shallow pipes under driveways.
I'd say it wouldn't be worth the effort. As above once you stop the draughts with ply and have the lvt down it won't feel as cold. Insulation would have to be thick to make any difference
I found with lvt never felt cold feet in bathrooms no need for ufh. Electric towel rad was great on other hand. Drying towels for a few hours after shower when the heating wasn't coming on.
Have you seen proper self compacting concrete? Im not just talking about a wet normal concrete. There is 10mm agg, admixtures and fibres in the proper stuff. Ive never had water added to it and the last batch I had came from what was at the time one of the most advanced batching plants in the UK. There was an article about it before a national bought them out.
It is good. Ive never had reason to complain about it. Never had to use SLC on it either its that flat. Always seal my dpm up well as like you say, its runny.
Price wise it did used to be getting on for twice the price. But the rep helping you lay it was included in the price with all the gear they bring. It always made economic sense to me.
I dont understand all the hate for self compacting here. Ive used it on every house I've built. Whether its ground bearing slab or being used as a "screed" ontop of b&b. Always had the wagon back right up to the house and pour it in. Rake it about, dapple bar and get the sealer sprayed on. Very flat and has always been level enough as I've always poured to the top of the blockwork at dpc level. Back in the lafarge days they sent a rep/concreter out inc in the price to help you with all the gear. Last lot I had needed to pay a guy to help who the concrete company reccomend. It certainly doesn't do the job for you but its a lot easier and better flowing than normal concrete.
Ive had kommerling before. It didn't seem any better or worse than other upvc profiles. Does it depend on the supplier? Do the foils last as long as the frames or do they deteriorate faster?
That trax pipe is expensive isnt it. I had a place 40 odd metres from the rd. Standard gas connection is only like 32m max or something round here. I built a dwarf wall at the max length point and split the ducting here thinking was gonna need the trax. The gas guys just took it all the way to the house for me without even asking. There was a comment after about how it was over max length, a drink to all the crew seemed to quiet that!