Mr Punter

There will be guidelines regarding overshadowing of garden, loss of aspect, loss of light into habitable rooms, overlooking and loss of privacy. Also in keeping (style, scale etc), following front and rear building lines, following the pattern and spacing of neighbouring properties. If you are doubling the footprint and demolishing the garage, it may be worth demolishing all and starting from scratch. At least it will then be VAT free.

The fan noise on many of these systems have a sound pressure of between 20 and 50 dBA depending on the setting they are running at. In heating mode, the warm air is directed downwards to avoid any discomfort. I find that hot radiators, especially with the fins, can set up currents of hot dry air that swirly around the room.

Is that a fibreglass liner inside the clay pipe? Maybe a repair?

You can get white sand in some parts of the country. Also white cement and hydrated lime. Use a gauging bucket if you want it consistent. 1:1:5 cement lime sand.

Sack the planning consultant. They have cost you £25k and were not capable of communicating with the planners, leading to s straight refusal instead of a simple amended plan. The appeals take several months and you may hear nothing until you receive the decision. Here is their current performance: https://www.gov.uk/guidance/appeals-average-timescales-for-arranging-inquiries-and-hearings

The sills look good. Is it down to your builder to measure and source them? Can you let me know who supplied them?

That looks mental. Draw a circle and use a jab saw.

Door closers are no longer required on houses. I doubt you would need to concern yourself with building regs as the age of the house precedes them.

Terrific progress. Can you let us know your anticipated total costs to completion?

I have some small flats and would be interested in the A2A units to improve the EPC rating, but I don't think they appear in SAP.

I don't like the way you end up with loads of pipes close together on the home run in ufh layouts.

It may be useful if you could get a cheap (self adhesive?) 100mm grid layout mat. Maybe 1m wide rolls.

The boot lintels are supported on the inner leaf and don't have an overhang. I think they fail quite often though.

Now that really is a whopper. It looks like the room was sprayed but they still got some paint on the socket.

Painted. Sand : cement : lime site mixed or OCR in bags. Paint colour lasts far longer than most of the through colour.

Could be a concrete boot lintel.

Some thoughts at random: Locating the CU centrally could save some cable. The fewer the penetrations through your airtight layer, the better. CU takes very little space. I tend to locate patch panel, hub, CU and TV / coax in the same place. It will be worth incorporating the MVHR ducting and SVP into the plans as these may need a fair bit of boxing in / risers. MVHR takes a lot of space and ducting. If all this is detailed on the plans, your contractors are less likely to just smash holes through where it suits them. You will need a very special door and floor makeup if the garage is to be PH and if you have that, why not just heat it and add it to the conditioned space? I guess your designer has detailed how to avoid the cold bridge junction with the top of the garage wall and the bedrooms above? Not to do with the OP but 2 bathrooms in a big 4 bed house is below what most buyers want so you may want to incorporate future provision for an extra ensuite at the design stage.

I have mains interlinked detectors with lithium battery backup plus sprinklers in every habitable space and on escape routes. I agree on the Aico ones plus the test / hush / locate control. I am 4 storey. For small two storey you probably just need a SD in the up and down halls plus a heat in the kitchen.

I quite like a hardwood threshold.

Standard for plumbers. They also like to leave all pipework uninsulated so you need to drain off a fair amount of tepid water before the hot or cold start flowing.

I have used this https://www.squaredealupvcshop.co.uk/product/hardie-top-vent-strip/ in the past but it is quite expensive. I have also used stainless steel mesh on a roll, stapled to the battens https://www.amazon.co.uk/Stainless-Insect-Mesh-0-94mm-0-22mm/dp/B077XY6PWJ

Sand cement screed is 75mm plus, liquid is 40mm plus.

If it is anhydrite and you want to tile you should remove the laitance or the tiles may not adhere long term.

I have used this stuff before: https://www.tradebuildingproducts.co.uk/products/sikagrout-111-gp-cementitious-general-purpose-grout?variant=41399952539801&currency=GBP& Do a frame of 2 x 2 around the base plate held in place with a couple of bricks.

Treated is not required internally, although you could use it for sole plates in case of minor leaks / floods.