torre

Have you asked them what about the project makes them unwilling? How have you determined they're incapable? I'd try and answer those questions before shopping around too much further or burning bridges with anyone already approached.

I'm surprised this hasn't come up at an earlier stage! No personal experience of piling but if you're only 4m away then I think it's likely the party wall 6m rule @SteamyTea linked will apply as you'll presumably be piling quite a lot deeper than the bottom of their foundations. In your case say they've a 1m strip foundation and you're piling deeper than 5m then PWA will apply. Bear in mind that you, not the piling company, will be liable to your neighbour for any damage to next door when taking the pilers advice. Have you already spoken to the neighbour at all about your piling?

Alternative to the chalk line is a membrane with a printed grid

I like the idea of a shadow gap, but getting the detailing right looks tricky!

It reduces thermal bridging at the wall/floor junction, so helps with SAP calculation. I'm sure I remember reading an old thread on here that discussed relative performance of a row of marmox blocks versus lightweight, if you can find it

I think 3k/m2 is more realistic to budget for if you want reasonable quality and aren't doing that much yourself. How much can you derisk the project? Did you PM last time and did you go over budget last time and by much? Could/would you use the same builder/trades?

Swings and roundabouts as you say, but this isn't quite accurate. A 100mm inner leaf of the best thermalites (0.11 W/m²K) is the equivalent of over 30mm of cavity batt 36 and the best 7N blocks (0.18) still close to 20mm equivalent. Multiply that up if you're using 140mm blocks or blocks on the outer too. Also, you might not guess it but even +25mm on the cavity equates to a 2% reduction of floor area in the average size home (around 49m2 per floor versus 50m2).

Signed off by whom? You will certainly need to have satisfied all planning conditions, or it's not a lawful development in the first place. Relevant Planning geek article (we needed a NMA to install our solar during construction as it wasn't shown on the plans, even though clearly PD after)

You can get a good idea of the difference by going on ubakus or similar, configuring your wall build up and swapping the block type and seeing how the u value changes. Switching out thermalite for something like fibolite could take you from say 0.18 to 0.19 and if you switched to a dense block even worse. Might sound a small difference for SAP but houses have a lot of wall area so it will suffer. If you're talking about dense blocks, you'll save on materials but lose some of the difference paying more for labour.

I'd be interested in how this complies with building regs minimum extraction rates etc or if you supplement with extract fans? It also looks very humidity focused, MVHR seems like it'll do a better job of reducing CO2 levels.

Apparently they're subsidised by the grid for helping balance demand which may help explain the pricing. I'd work on the assumption you may have to buy out of the contract (and get a cost for that, it'll probably be more than the subscription) if you want to sell - says the contract can be transferred, but similar leasing of the solar panels themselves has caused problems for plenty of people when selling.

IMO this is a huge improvement over what you first posted, more coherent and less mass. Second floor rear dormer as a balcony might be nice, neighbours might disagree. There's a lot of glazing on the side elevations and you may need to compromise on that, use obscured glass, to avoid privacy objections. I think in real life you'll struggle with the front door now opening direct onto your central open plan area. Fine for guests, not so much for the door to door sales etc.

Pretty sure Idealcombi aren't part of Dovista @Mr Punter but I agree Velfac are, and worth a mention. We were quoted quite a lot less for both Rational and Velfac versus Idealcombi. Neither's slider is that slim though. Lots of slim options around based on Cortizo Cor Vision but @rufiec if it's for a new build you have to be really carefully around PAS24 as most won't be

Starting with which way up you fill the cone!

Have you checked they're using the same delta T when quoting output? Any radiator can produce much higher output at a higher flow temperature, but like you, I'd be suspicious of one performing so much better than another of very similar design.