Conor

Something like 50mm eps glued to the inside would probably be enough. And lag the pipes.

You'll need continuous ventilation for the pitch roof at a minimum.

I got two lines of festoon lights. Brilliant. Worth the 30mins or so to screw in to the walls /ceilings. I've still got one setup on the underside of our balcony before I put in"proper" lighting. half tempted to hide the wires and leave them there instead of spending £200 on LED spots etc. I didn't bother with 110w, just 240v, perfectly safe if you've a properly installed board.

1. You don't need to use 22mm pipe at all. 15mm is fine for a shower. 2. Direct pipe routes. 3. Use 10mm pipe for basins. 4. You're over complicating it. 5. One pipe per fixture. No joins.

The sewer is public and you should be able to connect your foul sewage to it. It's nothing to do with your neighbour. It's not surprising the water company don't know anything about it, the pipe would never have been surveyed or drawings sent to the water company. You'll have to make an application and submit plans. There might be issues with that pipes capacity or the local network's capacity that will need to be checked by the water company. You WILL need to deal with surface water separately.

Can't normally share a domestic supply between properties. you'll ultimately need an independent supply for the new dwelling. That will be when you mortgage or sell. Bite the bullet and get it done now.

200mm insulation then liquid screed. So fairly typical except for ring beams instead of trenches, as we were already down into firm ground. External walls were ICF with tanking. We originally had it designed as an insulated raft, but SE couldn't get it to work.

Before it was finished, but you get the idea. Our reason for doing this was because it's a basement, we'd already dug out 400tonnes of earth and didn't want more coming from trenches.

That's what we did. Ground bearing raft. Where there were internal walls, the concrete was thicker with an extra layer of mesh. Walls were built off the slab. We also and compacted the Type 3, then the digger driver scraped out the areas for the walls, compacted, then blinding layer. Essentially extending the ringbeam internally.

No, just get it done. Ours was done in December. we only had a small area wash off. The silicone renders cure quickly, even in the cold.

We did it exactly as your building is proposing. If you don't have insulation, fitting the UFH is harder work as you have to attach to concrete rather than soft insulation. yes, perimeter insulation is needed as acts as an expansion gap.

So is all the driveway drainage going in to the aco in the middle there and then to a soak away? Where does the water go when the aco and soak away are overwhelmed? I hope there is flow to the road? Otherwise your house will flood. BC would not accept our patio drainage for that reason, we had to install a separate set of drains incase the primary got blocked or overwhelmed. And indeed, it's happened once that i know of. And agree with Jimbo, you're going to have damp issues all along the front there. An alternative is to install an aco channel drain all along the edge of the house, rather than the bricks. No caps on channel is fine if thet are up against something solid. Would be an issue if loose material could collapse in.

Where is the water coming from? If you're going to cut out and relay, I'd fisning the new surface 5-10mm lower, then come back a week later with a bag of self leveller.

Turn flow rates of your ufh zones down a bit.

Is your heating system working as expected / adequately?