Mr Punter

Your bigger problem is that the way it is set up with the insulation and shower room it will rot out within a few years. You have a cold flat roof and there should be a continuous air gap above the insulation so that there is an easy airflow path all round. You don't have this, so any warm moist air from, say, the shower, will find its way up until it meets the cold decking and roof joists where it will condense keeping them coated in water, with no way to escape. Unless you have insulation above the decking this is a disaster.

Well, they seem to have the correct Declaration of Conformity, so fill your boots!

Well you can only play it from where it is. Do you need to obtain Building Regs, or can you just ignore it? You may be able to obtain an indemnity policy for future sales so that the buyer would not risk being pursued by building control for the breach.

I have used a slate hook to lift them up. It just fits between the tiles, rotate and lift.

Unless they have lined them with greaseproof paper I can't see why multi finish won't stick. I doubt you can reclaim VAT on these.

I wouldn't want Building Control to ask about them but if this is just standard boards, not for structure or fire resistance, it is a good saving. I bet the likes of @nod get plasterboard cheap.

If it is lightweight it could alternatively be expanded clay, such as Leca, but either way at a metre thick you may not need to add more insulation. Find out exactly what you have and do the calcs. Yes, you can lay your limecrete on this once all the timber has been removed.

Next door looks a bit rough as well.

The dishwasher is faulty and a fire hazard if you don't fix it.

If it is rainwater nobody will care. 25m will be fine.

One of the best builders I know has no formal qualifications but has been in the business for over 40 years. He is very successful and sought after. His day starts at 5:00AM and he finishes around 7:00PM as he also has a small farm business. His literacy is limited but he can read a plan and spec.

That looks far too close to ground level.

I don't expect you will be going for drinks with him any time soon. So you are leaving them to do the brickwork only? You will still need scaffolding up to do the roof. It may be simpler just to part ways now, but you know him and the project better than we do.

Well that has messed with your plans! For the internal wall you could chop out sections of timber and infill with brickwork. Maybe for the outside walls you could cut out sections of timber with a recip saw and infill with brickwork. Any timber left will probably rot quite quickly and any fungus may travel through the brickwork in search of food.

Why don't they just correct the errors? 100m2 of additional wall area is significant. It must impact on building volume, footprint, ventilation, airtightness etc.

+1 it looks like the rear is parting company with the front. Just keep an eye. What is it like at the base and the other side?

Yes you need a rest bend. You could also have an access to the stack about 1m up in case it gets blocked. You could have a small inspection chamber downstream on the underground if you need to connect other pipes.

Good to see Pasquill stepping up on this. Well done them and @boxrick.

This plus plumbers and electricians not just mutilating the airtight layer. Unless you are doing MVHR with the associated install and maintenance issues I am not convinced that anything less than 3.0 is worthwhile, especially on a smaller property in the SE where mains gas is available.

The OP "wanted to gauge what target (and actual) people have had for air tightness in a traditional block and brick masonry build?"

I just had an air test done on brick and block flats and they were just under 4. No mastic or sealing as I did not want to get less than 3 and certainly did not want MVHR ducting.

It would not be an ideal first self build and unless you were skilled and experienced you could get your fingers badly burnt.

Turnkey including all fees, main contractor £1M, you as full time project manager £750k.

It will be much easier to tile a square one. You could get this in stainless steel and it may look better.

A good result. Did your builder use insulated cavity closers on the sides of openings for doors and windows, or close them with blockwork as per the drawings?