Mr Punter

Any chance of breaking out the old floor so you can get it properly level and insulated?

Yes, take at brick out. Could you also insulate the pipes? Wot Nick said

You can do them in shorter lengths and pack under the bits that need to be fatter with some timber.

I once had some very big 2g units and the panes had touched in the middle so some of the coating came off. Had them replaced. Get the rep out to look. They will try to swerve but you will get a feel for whether it is acceptable.

Do you charge a higher rate to fit the Habito? We used Fermacell on some flats a while ago. Never again, but the Habito looks good.

https://www.screwfix.com/p/turbocoach-coach-screws-yellow-zinc-plated-8-x-120mm-50-pack/52740 You can sink the heads in 10mm with a spade bit. 3 ply 45mm = 135mm. Your 90mm will not have any embedment in the 3rd timber.

I don't think there is much in it. Use whatever you have. I understand the soil pipe may be more UV resistant than the below ground.

The metal I studs are a fair bit stronger than the C studs, if you want a freestanding wall. We used it to line a tanked basement. The metal frame guys can put the stuff up very quickly. I / we can't.

I don't think the noise of the water will be an issue at all. More likely to hear the water as is goes down the sink waste, not once it is in the pipe and running steadily.

I would run the waste right to the end of the kitchen units in 40mm. It looks like there is a void or some insulation behind anyway. Run it to a decent fall. I don't know where the drain is outside in relation to your plan. 23m is not a particularly long run. if you know the invert of the drain we can let you know if you can let gravity be your friend.

The breather paper is normally stapled to outside of the panels so I suppose you could build panels on the ground, breather paper them and lift them into place. A bit of fiddling where they meet. I think it is most useful for weather protection before the external cladding is complete, so not really that important for you. With your inside membrane, do this as carefully as you can. Return it into windows and doors and down to the floor. If you can marry it up with floor joists, even better.

100% appeal. If you post up the refusal letter and anonymise it you may get some useful suggestions for the appeal. The planning officer report can also prove useful.

Sand / cement screeds (which you have) are normally 60-80mm. Liquid screeds are 40-60mm. Either one is fine with UFH. 30mm is too thin. Are the UFH pipes embedded in the screed? How are the levels at doorways etc?

Why not just use a buff colour mastic sealant?

Been waiting 14 pages for this and the pipe has sunk like the Titanic. Jesus what a let-down! Let us just say that @pocster may be left wanting.