Mr Punter

What a cowboy. This needs to be insulated to comply with building regs in England. I can't imagine this being different in Scotland.

I would use type 1 to part fill where it is over 50mm and sharp sand elsewhere, compact with a whacker to get it nice and level. Cleaner and more forgiving than concrete and simple to DIY.

I can't see it being an issue as your current system looks very simple

I am with the 900mm being too small to be of any use. 1500mm depth means you can have a table and enough room to get round one side. Can you make it deeper? I assume this is supported on posts and they are properly detailed at the base so they don't rot? You will need an outlet and downpipe for the drain. Will the drain channel have a built-in fall? What is the plan for the soffit underneath and the finish on the sides? If this is going the be used and is overlooked, consider using obscure glass so you are less exposed.

Has an engineer looked at the building? It is important that the external brick wall is properly stable and restrained, otherwise it may compromise the structure. If you want to go blockwork internal, it must be built plumb. You will need a selection of wall tie lengths. Do as @PeterW suggested with blown in beads.

As above but fix horizontal resilient bars to the vertical battens before fixing the plasterboard. Seal all the edges with mastic before you fix skirtings.

If the trusses are cheaper for supply and fit then I would go with them. Metal resilient bars are cheap and if you fit them at right angles under the trusses before you fit the plasterboard ceiling it will cut down on noise. You could always double board as well. Add some Rockwool acoustic insulation in the floor void. Take a look at the suggestions from plasterboard firms as most of their solutions are properly tested / measured for sound attenuation. Really like the 3d btw. Who did it? And welcome to the forum!

I guess there was no dimmer. Was the fitting reasonably well ventilated (not covered in insulation)?

Actually I noticed a few. Please strim and re-post. Quite shocking.

How are you dealing with the foundation for the new wall? How far out of true is the existing? Did you look at doing the inner leaf in timber frame, as you only need a residual 50mm cavity and you can insulate in the depth of the frame.

The LA are not going to do anything about it. It is very difficult to control the use of privately owned property. You may be in hot water if you rent it, however. Carpet and stairs could just make it a games or hobby room.

Maybe also consider Leca expanded clay beads to fill the void

Where we are (Sussex) the electric people insist on smooth ducting - 32mm single phase, 50mm 3 phase.

Does the trench go right up to you house? Is the water level anywhere near the underside of your floor? If there is some sort of spring it may be good to intercept it higher up and divert it outside your house footprint, assuming you are on sloped ground. I can't see why the water co would care unless there is nearby contamination in which case you should use barrier pipe. I would be tempted to line the trench and pipe with building sand as gravel may have a french drain effect.

Probably the neatest building site I have seen. Manifold looks very, timber frame with double noggins. Did the architect detail where the windows would go in relation to the frame and external cladding? It is an easy detail to slip up on, but simple enough to remedy. Are you on a deadline which must be stuck to (tenancy ending or whatever)? If not, just award the project another few weeks and give yourself a pat on the back for what looks like a first class job.

...and maybe change out of the profile picture outfit on the day?

It could be that they are a fairly small outfit and will not be willing or able to represent or defend themselves, in which case straight to court. You will still need to prove your case with evidence to the satisfaction of the District Judge (or whatever they are now called).

Sorry - I missed that. If they have the same strength and stiffness, chose the one that is cheaper. I guess the 18mm is lighter, which may make it easier to install if you are doing it on your own.

Go for 22mm lay at right angles to the joists. Normally try and lap the end on a joist and stagger the laps by half a board. I like D4 glue on the joists and on the tongue. Screw the boards down.

Not sure of your supply pipe. We have a sprinkler system at mains pressure and achieved over 100l / min at the inlet valve, so <10 mins for your tank. A couple of months ago before the pipework was properly secured and boxed in one of the kid's friends opened the front door and the handle hit part of the valveset and caused a fitting to come apart. It took about 2 minutes to shut off, by which time the ground floor of the house had about 5-10 mm of water throughout.

11mm feels much stiffer and the price difference is v. small. If you OSB it may be prone to mould. Some of the MGO can be left without even painting the underside.

Magnesium oxide board (MGO board) might be good. It will stiffen up the roof a fair bit too. Water and fire proof.

You will need access at the base of the stack up to the main run plus access to rod the main run.

This is very difficult to work with without specialist equipment. We did 50m in 90mm O/D for a pumped application. Even on a hot day it took some serious wrestling before it could be placed in the trench. Also you have the issue of connecting the ends which will make it far more trouble than it is worth.

I would only run drainage under the slab where it was not possible to do otherwise. If you can achieve a min 1:80 fall by running outside, do this. You can change direction with an IC. The biggest financial risks in housebuilding are foundations and drainage.