Mr Punter

I have also used Polarwall for a basement and found them very helpful. Construction is pretty simple.

You should also silicone the verticals on the tiles where the walls meet as they are a weak point.

Well done. Any chance of a mixed case of vintage Krug and Cristal?

Ask now for his agreement that you can get someone else to use his plans for Building Regs and Construction drawings. It sounds like you are nearly there with the planning drawings and if he is on a fixed price he may as well get it submitted.

Without a protected staircase that would be dangerous in the event of a fire. Upgrading the fire alarms with an interlinked mains detector in every room would be a way to mitigate, so that you would have a good early warning. It would probably be better than an upper story escape window.

No you would need planning consent Here is the guidance: https://www.gov.uk/government/publications/permitted-development-rights-for-householders-technical-guidance/permitted-development-rights-for-householders-technical-guidance#class-b--additions-etc-to-the-roof

For clarity please confirm that was the external temperature!

Maybe put down some porcelain tile or hardwood. It is too late to grieve about the mortar colour. I am considering using silver sand, white cement and lime on a project but I may just go with whatever is cheapest. I would need the brickies to use the special mix for the external brickwork only. Odds on they just use it everywhere.

My point was that they are uninsulated and still score better than @Marvin's place which is highly insulated.

I have some flats with electrical resistance heating and hot water, solid uninsulated walls and single glazing and they achieved E.

How did it pass SAP?

I would not fancy tiling once the units are in. This is the second one of these kitchen onto damp screed topics this month. I think it is best to delay the kitchen install. Get the floor tiled and grouted first.

I have worked on sites where if you are planting trees in the winter the hole you have just dug will fill with water before the tree is staked. Make sure you have paving where you are going to walk or you will end up with an unsightly track over your new lawn. As above, 150mm topsoil is what you paid for.

Airtightness, boiler controls, PV (should be good on a bungalow), accredited construction details all make a bit of difference. Get Jet floor to spec the floor to the u value you would like and get the SAP guy to use their value. If they won't / can, just use normal beam and block with a bit more PIR. Will be cheaper. Can you do ground bearing floor, or are conditions unsuitable? Floor insulation is cheapest and easiest compared to wall and sloped roof.

I really can't see how the small kink in the wall makes it a side elevation.

It is good to have a slight fall to the outside so any moisture or condensation runs away.

Including crack control is a really good plan. Even better if you can place it centrally under the door and start the tiles either side, with mastic instead of grout but I think once it is fully dry you could get away with filling the crack and tile straight over.

Do you have a plan of the building as originally built? The LPA seem to think they have, and your application does not fit in with PD. I cannot see how the conservatory could be considered part of the original dwelling.

I sounds like 81/P/00235 may have added on to the side of the house. Can you post the plans from that application, as that is the one the decision is based on? From the reference it may have been 40 years ago!

It is very messy and does not come off your hands for a couple of days.

It depends so much on ground conditions, access, loadings, contamination etc. Just get several prices and see what works out most economical.

I have used them a few times. You really just need to shop around and compare prices. They did a slab supported on driven steel piles, one on hollow stem drilled piles and one with open augered. Roger Boulivant are also a good firm,

Zinc is expensive and difficult to DIY. ASHP seems to be the winner over GSHP. You could get it priced in brick / block (by others) with a tiled roof (by you). There will still be plenty of work to keep you busy.

Is the whole bed "fed" by a trap door above?

I think it could look quite crisp to have the wall and roof meeting seamlessly. I can't see a reason it would be an issue. The are some uni halls near me that have this and I think they are finished in clay tiles.