Mr Punter

The battens and 25mm airflow path means that it is not essential to have the VCL. The insulation is not bridged by timbers so all looks good. 150mm insulation would have been better, but what you have looks OK.

Compare the cost of your special I joists with solid timber joists.

Can you have a rethink and do a beam and block floor? Much simpler than suspended RC. You need at least 150 air gap under, 225 preferred. Insulation on top, then screed or chipboard.

That sounds fair enough.

I buy the firrings from a local timber merchant. You can put them on top of 4 x 2 or 2 x 2 to make longer lengths. You could also have a ridge down the centre and fall either side. More gutter but it will be symmetrical.

I sent plans to Wunda and they gave me a price the next day. They will also do a design for you if you want to go ahead. If you are heating up 150mm of concrete it will take an age.

Also one one project the local fire authority were willing to relax their requirement for a vehicle turning head on the drive sized to accommodate a fire appliance so it is worth engaging with them.

Probably cheaper with conventional joists. Run the firrings in the same direction as if you run then perpendicular they need to still be 40mm at their thinnest.

A type that does not work, it would seem.

What is the piling method? Even if the works do not fall within the Party Wall Act (within 6m of your building) your house should not be "bouncing". You could get in touch with the LA Environmental Health and complain about the excessive vibration. They could do some monitoring.

You could also coat the brickwork with Stormdry. BC sometimes accept it if cavity tray is not practical.

Floating chipboard will work out and be cheaper. Use 22mm chipboard and glue the floorboards to it.

Sprinklers and a tank will normally be acceptable.

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.