Mr Punter

You could try just painting the wall above with StormDry, which is supposed to last 25 years.

Well done on progress so far. It is certainly no fun doing this but I have seen a number of sites near me where the contractor has had to go back to remedy issues. The recent weather has brought lots of defects into focus. Once the soggy insulation is all stripped it should be easier to see what has gone wrong.

Dreadful for them but I did smile when I saw they were called the Adams family...

75mm would be better. 100mm preferred. 50mm only gives you 1:120. Make sure it is properly supported with a bracket every metre.

You need the roofer and the window people on site for an inspection when (if) the weather improves. Between them they should work out what has gone wrong and suggest a remedy. As others have said, junctions are the most likely area of failure, especially if they are not correctly designed and detailed.

VCL is polythene which vapour does not travel through. Plasterboard is vapour permeable. Odd that the studs either side of the original window opening do not go down to the sole plate and that there are two top plates. Did the design change after manufacture / design deadline?

I scan read the first post and thought they had fitted windows throughout. My estimate was based on them fitting them all and I assumed they fitted about 55m2 of windows at about £60 per metre. Agreed that £2,500 for a door and a window is excessive. How much was that per m2?

The self build VAT rules seem a fair bit stricter than those for developers.

No need to do decoration or tiling. You need to fit sink, baths and WCs to test traps, complete electrics. Get them over and if BC want more work done before final they will let you know.

My guess £3,500

I have appealed a couple of bandings successfully some years ago. It was possible to have a dialogue with the assessor and they seemed fairly amenable if one was able to give evidence of similar houses in a lower band than they had proposed.

The plans that @Ivan_England posted show a full basement in the proposed new house. The footprint is close to both the neighbour and the donor house so the excavation will need support. This could be done with driven sheet piles, trench plates, secant piles, king piles etc but will be very difficult and expensive. While the basement retaining walls are built they will need a bit of working room around. I would not consider building a basement in that location.

We have built near a river. The houses have brick and block ground floor, rigid insulation, electrics set above 1100 from ffl, suspended concrete ground floor, with flood proof airbricks and porcelain tile finish. Ground floor walls are rendered internally. Ground floor use non-habitable (store, gym, office etc. Bedrooms, kitchen etc. located on upper floors.) Skirtings and a few areas are sacrificial. We are also looking at adding some flood barriers for ground floor openings at a cost of about £2,200 per house.

I do not think that the garden wall is a structural retaining wall. It looks to be 100mm thick with 215mm piers. Your engineer will need to consider temporary as well as permanent support to the neighbouring structures. That basement will be a bit of a challenge!

I concur that it does sound rather - um - unusual. I understand that @pocster once had a tenant who left items of a similar ilk.

If the issue is saturated brickwork, you could paint it with Storm Dry. I think this works OK where there is no cavity tray above conservatories and porches. Very long lasting apparently.

Here is the one they designed: The top floor had skeilings so the vents could not go in the corners. Timber frame designer unhelpfully put a strongback where it got in the way. This used 125mm rigid duct. I think the flexi stuff with the manifold boxes would be easier to do.

I once sited a Vent Axia Sentinel Kinetic Plus in a small loft as per the specialist design. You needed to be a contortionist to clean the filters and I doubt the current owners will have ever done so.

LVT flooring is only a couple of mm thick. Just lay it under the dishwasher, sink, washing machine and leave the other bits as bare ply. I like to mastic round like a dam so if anything leaks it will appear from under the plinth.

Like something out of Mad Max. Not sure I would lift a pack of blocks like in the last pic without a change of underwear nearby. Let us know how fast you can drive it!

Agree with @PeterW about the shower. We have one that is 1800 x 700 and it is a bit cramped. Can you have the sink and WC on the same wall?

Room dims might help. Can you add them to the drawing, or will that spoil it?

You would need to do all the ducting and room terminals plus electrics and condense drain but you could leave buying the unit until later.

If there is a screen or panel to the shower don't go less than 600mm. Is there a WC in the far corner? If this is an en-suite maybe used in darkness the layout may need a rethink.

Cut a piece of OSB bigger than the infill and screw it to the face. It lasts a surprisingly long time.