Big Jimbo

If it is a rainwater system, then you can connect with permission. If you want to go into the foul system, then expect resistance from the water authority.

The PIR, when taped, will act like a vapour barrier anyway. So you are defo overthinking.

Batten on the side wall and Two part velcro. Easy on and off. Either that or magnet catches. Both available from screwfix i believe.

The external motors from "Best or Westin" that i used to use were expensive at the time. What ever you do, make sure you have a grease filter at the start, source. Try and keep bends to a minimum. Every bend with have a big effect on the airflow. If you can try and keep your pipework round. Again for the benefit of airflow. If using round pipe, try and get One that has a smooth inside. Again air does noy like going passed loads of ripples. Best of luck with the project.

You should have tipped it into his air vent @Kelvin. Nice one fella.

4 small blobs of silicon. Dont go mad, just incase it ever has to come off.

To be honest @Nickfromwales, I told the surveyor to not even bother quoting for a new supply. I was that Peed off. The only actual quote i received was £2k for the split of the existing 3phase. 100amp for each property will be fine, even if i chuck a bit of solar on each house.

@JohnMo Good questiions. Sounds like The firm building the house will simply be the main contractor. But i agree, it is confusing ? I will try and put my own situation, which sounds similar. I Own the land. I have a building company. Limited. It is dormant but i file returns. I instruct my building company to build the house, and i pay it, each time it issues me with an invoice. The company, builds the house, Zero rating my invoices as applicable. The company reclaims any Vat paid, every quarter as applicable. At the end the company shows a small profit, and deals with that as its own entity. I get the benefit of effectively not having to wait until the end to get my VAT back as a self builder. The above is my intention...

@Nickfromwales No mention of the transformer. Traffic lights, blah, blah, blah, Seems a joke at £24k. The cable is at most 750mm deep. I would have paid £5k for the future proofing of Two 3phase supplies, but, £24k buys a few materials for the build.

I don't know, but could you instruct the Limited Company to build the house on your behalf ? The limited company buys all materials, and labour, and reclaims any Vat paid, every quarter, while billing you, Zero rated as applicable. Effectively, You have a main contractor building the house for you ? The company does not own the land, or the house. You do ?

@jonny I know what you mean about cost. I have 3phase to my existing bungalow. Only One phase is metered. I have permission for knocking the bungalow, and building Two new houses. I enquired about bringing in a new 3phase supply. It is in the ditch outside the front boundary, and no more than 1.5 meters from my boundary. To bring a new supply, to a new cabinet just inside my boundary, i was quoted £24k. That was with me supplying the box at the boundary. My alternative is having the existing supply split, with each new property having 100amp single phase supply, leaving the Third phase unused. Cost £2k. Each new house is going to have a single phase. Im not paying £24k. Blinking ek.

That looks rough as IMO. A thin layer of EPS before you put the membrane down would do the job.

Yellow and green is for earth, so i expect you need an earth rod. It will have to achieve a certain, impeedence ?

Well done. Hope you enjoyed a cup of tea after.

At a first glance you will want to consider doing something with the huge void between the ceiling and the underside of the warm roof, where all your expensive heat will exit via the eaves.