Mr Punter

I am interested to know what they quoted?

You need a cavity tray (DPC) and weep holes above the openings. If there is a lot of brickwork above an opening on a wall that gets hit by the weather there will be a fair amount of water getting in. If there is a tray you could just install some weeps.

They like well drained soil and sunny position. Wet clay is a no-no.

Another vote for a pond and associated planting. Good for drainage and biodiversity and the garden looks big enough.

Hallhooks will be easy to fit.

Liquid screed can go down to 45mm.

In terms of ducting, if the fan is being mounted on the sloped ceiling, something like https://www.screwfix.com/p/manrose-round-to-rectangular-connector-elbow-90-bend-adaptor-white-100mm/96549 but you will probably need to cut the existing bit down with a multi tool. You need a 4" fan with a timer, plus 3 core and earth wiring which is normally taken from the light. The skeilings need insulating before they are plasterboarded.

It will probably depend on if your neighbour complains. Will it be higher than their ground level and will it increase overlooking / loss of privacy?

Normally insulation then screed. Don't worry about a small hole in the DPM. The beam and block is not in contact with the ground.

Yes the vents have a plastic periscope that goes below the beam and block. With beam and block you can smash out a block with no issues, but the beams need to be left intact. The beams may have intermediate support dwarf walls which could be in your way. On the upside, they should have at least 150mm space under. Is it far from the outside wall to the proposed sink waste?

If it is beam and block there should be several air vents externally about DPC level.

Could you mount handrail on the wall on the other side? Just have landing balustrade at the top.

I think it is often better to hire a decent sized (4-8 tonne) tracked excavator if it you are doing a one-off house. About £500 a week for a machine worth about £50k. You could do foundations and drains for most self builds in 2-3 weeks. If anything goes wrong the hire firm will sort it.

Part E will mostly not be relevant as this is an existing house. It has most impact for new build flats and houses where there are party walls and floors .

In my view the plan B scheme does not require freeholder consent. Without intrusive works it will be difficult for the surveyor to conclusively establish if the wall is load bearing, but is is very unlikely. I would just go ahead and get the work done.

Use Celotex instead of Rockwool. Even better if you top it off with insulated plasterboard.

Planners are often not keen to allow windows in habitable rooms at the side of a property for just the reason that it may prevent future development of the neighbouring land. I suspect that is why the room is labeled as "gym" rather than "study".

It looks like you have about 1m to the boundary. The new building will probably also be set 1m, so you have a 2m separation distance. You can install a 2m high fence on the boundary and that will prevent overlooking, providing the proposed bungalow floor level is similar to your ground floor.

I am not quite with you. Surely it will reduce the heat losses through the wall by improving the U value and therefore the room will stay warm for longer?

Yes it will help keep the heat in.

I am building 3 flats and thinking to fit gas boilers and leave it to future owners to fit heat pumps as I would not qualify for the grant but they will.

If you do the floating floor it is best to use 22mm t&g chipboard and bond the engineered floor to it. The adhesive is pricey but it feels a lot more solid.

I have not seen anything as small as those. S3i do a large range and may be able to point you in the right direction.

I have left them exposed in a conversion, but they were large beams. They need to be meaty for the char rates to count. https://www.designingbuildings.co.uk/wiki/Sacrificial_timber BC did not seem bothered but this was 8 years ago pre Grenfell.

Could you fit some noggins between them on the line of the supporting wall?