Mr Punter

They tend to be fairly standard but sometimes you may want to include neighbouring buildings for context elevations etc.

I have looked at this in ubakus and it all seems OK. U value of about 0.2 W/(m²K). I would not get too hung up on how to seal the plastic VCL to the insulation. The battens will hold it in place.

You may find it easier to use Wedi / Marmox type board as it is much lighter and easier to cut and fix.

If there is a warranty try the warranty company.

I could be if they have been leaking and made the soil weaker in that area. Get the vendors consent to roll back the carpet. Check the concrete / screed for damage. Tap it all over to see where there are voids. Double check gutters, downpipes and drains as well as water main.

It looks like they could do all the work from your side.

Hot wire is only good for polystyrene, not pir / pur.

Standard timber frame kit is studs at 600 centres and no noggins. Top and bottom rail plus connecting plate at the top. The noggins in the pic are for wall or tall units. OSB is for racking and strength. Amazing how a sheet of 9mm OSB stiffens a wall.

If the hole is too large or small the screw can seize up or not tighten. Also if you need to remove and reinsert the screw it does not behave as well as first time.

I like concrete screws but they can be more fussy than rawlplugs. Concrete screws are quite dependant on substrate you are fixing to and drill diameter. They are good if you are doing lots of the same - like battens etc.

Once the work has been done the PWA has no relevance. If they think you have caused damage, they could claim against you irrespective of an award/agreement being in place. If you were still carrying out works they could issue an injunction to get you to stop, but as works are complete there is nothing to be done.

If the base of your foundation is lower than the base of the neighbouring foundation you will need the PWA.

I think you would normally have solid full height blocking between the joists at the wall junction, maybe x 2. The scraps of OSB don't help as I think it needs a continuous bearing. Why did he not just run the OSB all the way along? If the decking is glued to the joists you may need to move the bottom of the joists to get them upright. I guess they are just nailed? I would want this agreed with your SE.

As per @DevilDamo. Excavation within 3m. Make sure you get a decent contractor as the existing wall will need to be made stable and safe while the work progresses.

Yes you should have a Party Wall Agreement. Get a quote from a Party Wall surveyor. They can act for both of you or your neighbour can appoint their own. You will pay for all. You could just ask your neighbour to consent, but from what you suggest they will not.

Timber frame, timber clad may be considered a risk by lenders and insurers.

For the extract fans, if they are standalone the information is on the manufacturers data sheet. You don't need to test each fan or pay any money.

That is quite an undertaking. I look forward to hearing more as you progress.

Your door track is creating a thermal bridge between the brick and the screed. A small strip of PIR before the screed would solve this.

The Marmox are 100mm wide or optionally 215mm. Depth (height) is 65mm or optionally 100mm.

This is one for your engineer. They should give you full spec, calcs and drawings for the connections. One column either end sounds simpler.

While you are gathering the information on the sewer (diameter, invert, material), find out where the water and electric is to make sure there are no clashes. It looks like you could set the proposed house back a fair bit.

I have fitted an Ikea Metod kitchen and was not impressed. There is no recess at the back and the plinth space is only 80mm high. All services can be a nightmare to accommodate. The wall cupboard hanging is bizarre.

If the wall is not part of the house I do not see the issue.

What is the point of the warranty if you are having to shell out so much?