Mr Punter

Why not build it and see what happens? Unless a neighbour decides to be tricky it will be OK. In reality you are not compromising anyone's health and safety. It is your land.

You will need a warranty or Professional Consultant Certificate if you think you will sell or finance in the next 10 years. The PCC route is fairly cheap and can be done retrospectively if needed.

I like the design. Have you looked at doing a blog on here?

Within a metre it needs to be non-combustible, so the log cabin is out.

I see MBC Timber Frame have a similar roof design: https://www.mbctimberframe.co.uk/passive-house/passive-roof/

It does not matter if you are within 6 metres UNLESS your foundation / walls cut through the imaginary 45 degree line. Unlikely unless you are piling or within 3 metres of their building. Party Wall matters can be expensive and time consuming, so if you do not have to do it, don't.

The membrane is heavy. Don't try to do it on your own. You need a fall on the roof of at least 1:60 so on your joists you could run firrings in one direction and then your battens at right angles to the firrings. If you go with the cold roof (which is far from ideal) you will need a very well installed vapour control layer under the joists to stop warm moist air condensing in the cellulose. Have a service cavity for light cables as well. The ventilation around the parapet is quite hard to achieve but changing the wall battens from horizontal to vertical would help.

It is hard to see without seeing more of the plan or elevation. I think you will need to alter this or get refused planning. You could move this to the right, reduce the depth etc. Is that a door to the kitchen? Can it be glazed? You will probably need to move some pipework but it should not be a huge issue. What does your architect suggest?

Nice. Who was the steel fabricator? I thought you had almost finished. What the hell are you building now?

If you are not interested in ROI and cannot put a value on your consuming home grown energy it is difficult to give an answer. It probably depends how much money you have! Can you not get a bigger inverter now and add panels later or is that not how it works? If it were me I would buy the 8K as it is a small price to pay to feel smug and virtuous.

Would it be terrible to move the kitchen window over 700mm or so and shift the whole thing along?

You would not normally need insulation to a floor above a basement. Bear in mind that the basement design may need a certain floor type to help support the walls. You will need to be careful if you have a suspended floor in the other part of the house as it would normally be ventilated and therefore cannot connect to the basement part. As per @Bitpipe, a full basement saves quite a few issues.

Make sure you paint the ceiling first.

I am surprised it is so cheap. Is that supply only? Does it cover all materials? As it is only single storey it may be fairly easy to add panels later, when they may become cheaper / more efficient, so could you go for the 4K and allow for later add-on?

https://www.bbc.co.uk/news/uk-england-london-54794723 I hope the insurance policy had a very large amount of cover as this could cost tens of millions. Property values in this street are £30,000 per metre! https://www.standard.co.uk/news/london/two-houses-collapse-basement-work-chelsea-b43428.html

If you have a hundred 5l toilets and 1 person flushes once a day it is 5l per person per day. If you have one 5l toilet and 80 people flush once a day it is 5l per person per day.

If you lay MOT first you will need to sacrifice a fair bit as it will be contaminated when you dig your trenches and even a bit when they install the piles.

If the piling rig is OK on your existing ground and that is confirmed by the contractor, do piling, then services then MOT / sand. Sometimes the bigger piling rigs need loads of ground preparation.

https://www.theguardian.com/environment/2020/sep/29/dual-flush-toilets-wasting-more-water-than-they-save

I think it is accepted that these regs are a bit silly and not really what building regs are about (Health and Safety) which this bit has become self cert. I heard recently that the new WC cisterns can often use more water than their old counterparts because people are unaware when there is a leak of water from the cistern into the pan.

Because a person will only use on loo at a time, so consumption is not altered by the number of loos, just their efficiency. They will take an average efficiency if there is more than one.

See if they will accept a Professional Consultant Certificate.

I don't believe you need the calculator, just a written statement saying "I confirm that water consumption is calculated at less than 125 litres/person/day using fittings approach”.

That looks a fair bit neater than the first one you did. Less adhesive in the grout gap. Can you promise not to use piss yellow grout this time? It that a very big l-shape to the left of the mirror or did you cheat?

25 years with the StormDry and it is non-hazardous and BBA approved.