Temp

Yes. In theory you don't need a ventilated void if its a breathable membrane. But the void is also to allow the membrane to drape. If you push it against the underside of the batten dirt can accumulate and form a mud that stops water running down. A pool of water can form causing the batten to rot.

What is the white pipe on the right hand side? Is it just leaning up there or in use? Perhaps replace that with a stack and connect the new into that?

If its a cold roof (insulation between/below rafters) the top edge should be ventilated. Is that why they left gaps under the lead? Not the best/correct solution. Google Abutment ventilation or roof ti wall ventilation. Example ventilation system.. https://www.wienerberger.co.uk/products/roof/systems-and-accessories/top-abutment-ventilation.html

Spray foam can be bad news.. Portsmouth News: Portsmouth woman's heartbreak as foam insulation scam makes her home virtually worthless. https://www.portsmouth.co.uk/news/people/streetwise-portsmouth-womans-heartbreak-as-foam-insulation-scam-leaves-her-home-virtually-worthless-3658803

Check the purchase price includes the FIT payments. I have heard it is sometimes possible to "take them with you" when you sell up.

My neighbour had some fantastic hinged iron gates on 8ft brick pillar constructed last year. They lasted a month before he had to get the builders back to fix them. That involved taking down the brick pillars and rebuilding them stronger. important to get it design right. Are your gates going to be sliding or hinged? Found.. https://community.screwfix.com/threads/iron-gate-footings.211575/

I think I would just remove any untidy looking bits (around the base of the door opening only?) and replace that. Leave everything else. See if anything leaks and address that. It can be hard to remove it without scratching chromed plastic.

If you win the lottery have a look at Copper guttering. Looks great but £.

Main thing is to make sure the guttering projects far enough as water can shoot off the end of tiles rather than drip off the end.

If the CIL is a thing in your area you shouldn't do any work on site until you have formally claimed the CIL exemption and got a response. You cannot do thus until after getting planning permission. It's not enough for the planners to just tell you it will be exempt.

I think it could be rejected. VAT708 Section 3.3.4 covers "Work closely connected to the construction of the building" but see section 3.3.5. For example demolition can be zero rated but is standard rated if carried out before you get planning permission.. https://www.gov.uk/guidance/buildings-and-construction-vat-notice-708 HMRC don't always check everything very carefully so there might be people that have got away with it and others that haven't.

How much of the pipework to the DHW tank is accessible?

Just want to echo what others have said. Never seen a pressure regulator/reducer used as a filler. Usually a flex hose with valves each end as others have said. Even if that regulator was allowed I'm not sure why there would be any need to apply tools to it to fill the system as it should do that automatically. Edit: I'm wondering if its some sort of combined regulator and isolation valve? eg when the isolation valve is opened it introduces reduced pressure water into the system. When the isolation valve is shut no water can get in. eg its NOT an automatic filler. That might make some sense as it eliminates the possibility of over pressurising the system.

As I recall it is allowed to share an open vented stack between several houses (5?). However most BCO prefer each house to have one, usually at the furthest point from the main sewer in the road. Their main purpose is to ventilate gasses from the sewer system but they can also help prevent water being sucked out of traps by fast flows like flushing loos or showers. If that happens smells can get back in. I would try and locate which trap is causing the problem. If it turns out to be a basin it might be easy to add a small AAV under it.

Weds 610 is probably as good as anything because it will be designed not to dissolve the foam. You could embed some mesh tape in the 610.

How old is the hot water tank? Any water coming out of overflows when you try to pressurise it?

Is there a reason for that?

Air lock in the UFH loops?

What thickness Engineered wood? What is the water temperature being sent to the floor? How much insulation under the UFH? How well insulated is the house in general? Do the return pipes get hot? What was the pipe spacing? We have Engineered wood flooring over UFH and 80mm insulation. We have a near two storey window in that room with no curtains. First winter we had similar issue, room not reaching set temperature. Had to crank up the flow temperature somewhat. Since then it's been OK. However other rooms with stone or tile floors have always felt easier to heat. Turning up the flow temperature is a risk to the wood floor but ours has been fine.

Don't neglect that "cavity tray above roof level". They are some work to fit but they stop water running down inside what was an exterior wall and coming through the brick into your new room. Otherwise +1 to tanking the wall to above ground level then battens, insulation and plasterboard.

This might be of interest although it's from 2020. It suggests planning conditions requiring mitigation may not be enforceable if its not possible for you to comply.. https://www.winchester.gov.uk/assets/attach/21906/CAB3219-Appendix-A-Position-Statement-Nitrate-Neutrality.pdf There are time limits to appeal conditions.

Can't add much, just that there are two different grades of stainless steel used to make flues. One is more resistant to corrosion than the other. Can't recall which is which but check it out.

If you've had to give them evidence you should probably start thinking about getting your VAT return in (3 month deadline).

In the letter here... https://www.north-norfolk.gov.uk/media/7687/letter-from-ne-water-quality-and-nutrient-neutrality-advice.pdf it says.. Is it as "simple" as providing a storm surge attenuation system? If it has to be done at the sewerage works perhaps thus is something the CIL should address? After all its meant to fund new infrastructure.

So have they basically vetoed any new connection to the sewerage system?