Mr Punter

Yes you will fill the gap between the rough edge and the extender.

Yes, the extenders are the way forward. Shame they were not fitted pre-plaster, but at least it gives something to fill to.

Your biggest challenge will be to get the concrete in the right place, as once it is poured you won't be moving it. If you can get the lorry near all the trenches, fantastic. If not you would do well with a concrete pump - either boom or line type. You will need minimum 3, preferably 4 people, plus the pump guy and concrete truck driver. Work out exactly what you are doing before anything turns up. How will the concrete lorries get in and out, traffic management etc. 6m is very wide to screed to. Can you get some pegs in the ground as levels? If there is a screed layer on top, the accuracy of the slab doesn't matter too much.

I have only done these in flats.

Not me. I would spec it on external render though.

As suggested by @ADLIan and @IanR, it is probably the thermal bridge calculations that are the issue. You are far better off using existing calcs than having custom ones. The default psi values are unbelievably negative and these are probably the ones that were used.

Bed joint reinforcement (the train track stuff) above and below the openings may have helped. I have only specified it on rendered walls or brickwork feature panels like stack bond. Mesh in the render also helps. You best option now is filler.

I saw these people the other day: https://anthonygold.co.uk/service/leaseholders-and-freeholders/conversion-to-freehold-enfranchisement/ May be worth another quote. Are the other leaseholders on board?

It looks nice and tidy. Did you concrete over a pipe there?

I know someone who used expanded clay fill, then concrete slab with UFH. It was a considerable depth. You will need a SE input obvs.

If the cavity does not need ventilation you could fit a DPC cavity tray around the base of the plinth bricks linked to the inner leaf and fit the mini weep vents at 900mm centres.

Well the good news is they haven't tried to cover it up. Get a full survey and report. Make sure it includes roof condition, timber condition, damp, dry rot and condition of brickwork.

So is this an insulated masonry cavity wall?

You need to confirm with the contractor that they will immediately spray the curing compound on the finished slab. If the water evaporates from the slab too quickly the concrete will not properly cure. That said, the house will not fall down.

If there is only 1 layer you will be fine with the overlaps. If you can get someone to help placement it would help a lot as the sheets are heavy and awkward. You may want some tie wire where the sheets join and allow for a 300-400mm overlap (40x wire size).

On a gable with a raking roof abutment and windows, it is hardly glory work!

Stapling the tape on may help straighten it up a bit. Get it clad ASAP.

Looks fine. I would normally expect to see vertical stapled on tape to identify where the studs are.

Keep the higher bits as close to the surface as possible, especially of it is path only. 300mm min cover is fine and you could do less at a pinch. Use the mini shallow ICs at the sides and back and for corners where you will add a 45 either end. Avoid clashes with the surface water system. Make sure the foundation is low enough where the pipes cross at the front. This can just be short sections.

If you are that tight on fall, could you raise the building by 200mm? Hardly noticeable I would think.

I don't know why you redesigned this. Are you short on fall? You have about the same number of ICs as the original. Not sure why the line at the front has moved 6 metres. It may prove another obstruction. Very large property! Can you feed the drawing to an AI chat?

I must say that if it means application details are easier to complete to LA satisfaction then the AI approach sounds like a win all round.

You could fully fill with 140mm pir between studs and line internally with 50mm pir, held on with 38 x 50 battens to create a service cavity. You could put the 50mm on the outside but you will need different wall ties and another layer of breather membrane etc. You will need about 30mm cavity to the brickwork. If the timber frame co quote for the insulation it saves a lot off faff and mess on site.

Insulation tends to be mineral wool or PIR. What is the proposed "rain screen"?

This type of unit MUST be installed and commissioned by a legally certified F-gas installer.