Mr Punter

If it is loose it is OK on a nice concrete base but a pain if it is not on a clean surface. Bricklayer will not thank you for mud and stones in the mortar. Even worse if it is used for render. I do find it much easier to shovel from a concrete slab than digging from a bag though.

I used this stuff https://www.stovesonline.co.uk/wood_burning_stoves/Selkirk-flue.html It is twin wall and I used the 150mm which has an external diameter of 200mm.

I don't think that HETAS registration is mandatory, just a way of showing compliance. I have done a metal flue in the past as part of a new build house, all to spec and Building Inspector was fine with it.

As I have previously posted, I think Fermacell is a right bugger to cut and fix. Very clever marketing.

Perhaps you could try the GGF as they seem well regarded in the industry: https://www.ggf.org.uk/technical-information/tech-consultancy/expert-witness/

Have you established if the leak is around the perimeter seal or is it in the window system itself - such as around the glazing gaskets etc? The former suggest prep, flashings, mastic / compriband / installation issues and the latter suggests manufacturer or damage during installation. Can you get in a reputable window firm who deal with several manufacturers and ask their opinion, even if you have to pay for their time?

Can you get rid of the branch on top of the elbow, just have the elbow and lift the horizontal pipe so it all has a really nice fall to the outside? You would probably gain 200mm in fall and therefore no issues.

Part E (passage of sound) and Robust Details mostly just applies to attached houses and to flats. For detached houses the only things to consider are including some fibre wall insulation around bathrooms and bedrooms and between floors. There is no sound testing required.

The foam is not waterproof so you need to cut it back a little and then use mastic to seal between window frame and stone. Alternative would be to cut back 20mm and use Compriband tape to seal.

Most warranty providers want sheathing board, breather membrane and a min 25mm drained and vented cavity.

Is it OK to use earth terminal strip in a backbox and lose some of the WAGOs?

Another vote for some quality repointing. Get a quote from a proper craftsman whose work you have seen. The plastic windows don't look good. If you really want to lose the mock Tudor look you could just re-render. White paint may be better. If you do clay tile hanging you would be best to have a different shade to the brickwork - perhaps redder.

With the sockets you could strip the cable ends and use wagos x3 to join earth-earth, live-live, neutral-neutral. You could then short all the wires one end and test for continuity the other end. A sparky will probably post soon with a much better suggestion.

300mm mineral wool on the ceiling and if you have enough space, around and over the rsj/blockwork, otherwise Celotex around and over.

I would get the merchant size (3.6 x 2.0) heavier duty A252 mesh as it will fit your slab dimensions and is easier to handle than the full sheets. You could also cut a sheet up to have a second layer near the bottom around the outside, but probably overkill.

You can run the joists either way and either build in or use hangers.

I would either close off the door permanently with a Juliet balcony / door restrictor OR fit edge protection. You could price up timber if glass is too costly. Consider the risks of the door being accidentally left unlocked and small kids in the house or you get someone else to do the tree work, they are talking on their mobile and take a step back. The reg is there for a good reason.

Madness. It is worth about £4,000 per tonne.

The design is not controversial. I would be very surprised if they could find good reason to refuse.

They need to see the smoke to work and the smoke will not get into a recess easily. I have Aico and they are fine. I guess yours will be more obvious with the mirrored ceilings everywhere?

I don't see why it cannot be replaced. It is not listed and neither are you in a conservation area. Get a decent scheme designed and submit it, as I cannot see why it should be refused. What the planners and neighbours "like" or dislike has little bearing on things, it is a matter of policy and a refusal would need robust justification.

Often there will be an elevation showing a neighbouring building and the proposed building. so it can be easy to compare eaves, ridge, thresholds etc. If not and there are no heights specified on plan, just make the heights above the ground level is the same as per the elevation drawings. Did the neighbour complain to you or to the planners?

I think if it is cement bonded and the existing slab has to be removed you may be best burying it under the new slab. It is entirely harmless in this situation and far more damaging if removed / planed down and deposed of elsewhere. I think you may be worrying about nothing, although if you do discover any materials that are unknown, get them dealt with professionally and assume they are higher risk asbestos.

You can get 7N aerated blocks as well. If you really want decent insulation for the soleplate you can use a course of Perinsul Foamglas or similar, but they are pricey.

As per others, low iron glass is what you need. Not too much more expensive but worth it especially when the glass is thick or you can see the edge.