Mr Punter

So, your proposed entrance is considered an improvement. Keep that in but revert to the approved windows elsewhere. You could try pitched or curved roof dormers if the catslide is not your thing. Perhaps post up what you propose before you sent it to the planning officer as this could be your last chance to get this through. Personally I think the officer did you a favour and you dodged a bullet there.

The insurance is fairly cheap and you can pass it on to future owners.

I think it is 64 degrees and more like confit than fried. It was the dish that inspired this place. https://64degrees.co.uk/

It is quite hard to understand what happened. Did they build in the joists and steel, then knock through, then rip 4.5cm off the tops, then fit the chipboard? Surely a plate fixed to the face of the wall at the correct height and some joist hangers would have occurred to them?

I have a feeling they still punish electric v. gas.

With the PV and ST, a combi may not work out. Also you may want to ditch oil in future.

Apple trees are not that thirsty. Unless you are on highly shrinkable clay you will be fine.

I often wonder why we have concrete when it is just a ground bearing floor, not carrying any building loads. If the ground is good and solid, surely hardcore and well compacted type 1 would be sufficient. Certainly better than brick on earth, which was traditional years ago.

There is a lot to consider here. What is the floor finish? Do you still propose to have roof tiles beneath as per the elevation? I note that the roof battens don't look to be set out for this and the heads of the ground floor windows look lower as built than as designed. You may find that a galvanised and powder coated steel frame could work to support any deck above the waterproofing and support the side and front balustrade. This is probably the most complicated detail on your house so it needs to be properly designed.

If the ground conditions are suitable, 300mm depth of concrete would be fine. I think 200mm is regarded as the minimum acceptable but must be deep enough not to be affected by frost.

As the balcony is inset it will need proper insulation, waterproofing and floor finish which means the floor zone will be thicker. You will either need a step up from the living room or a bulk head in the bedroom / entrance hall. Agree with @ProDave regarding the WC at first floor.

Because the house is fairly recent, if there are no signs of movement on yours or any neighbours you should be able to use the same foundation type and depth as on your main house.

It is only a small amount of masonry extending up and I think with blockwork there is less chance of cracking. You will probably want to have this meshed and rendered. What are you considering for the cheeks?

A while ago we hire a Merlo Rotating telehandler with rotating forks to load out plasterboard and insulation into a 4 storey terrace. Once the operator and supplier got it working it was a fantastic bit of kit. Pick up a pallet of boards, lift and rotate main body, then rotate forks so the boards can be easily dragged off the stack and into the units. We had it for 2 days and loaded out about 30 tonnes.

Sewage is potentially a big expense. Best to get mains drainage if possible. Depending on the amount of work you are up for, budget £30,000 for services plus £1,400 to £2,100 per metre for the conversion.

I am not sure if the figures include VAT? It looks like the all-in costs will be about £160k for the alterations and £340k for the extension, so £1143/m2 and £2428/m2. This seems doable but you will need to be very careful to make sure these costs are nailed down. I don't think a 5% contingency will give enough headroom. Prices are only going one way currently.

The worktops look fine but the wall are not right. Just paint the walls an off-white shade. Try a few out. Even your architrave colour is a better match.

If you have downlights or extractor fans in the ceiling of the floor below you could drop one or two down to see which way the joists run and maybe get an idea of spacing. Often they are at 600ctrs on house basher estates. Get some decent chipboard floor screws like these: https://www.wickes.co.uk/Spax-Chipboard-Flooring-Screws---4-5-x-60mm-Pack-of-300/p/140812 Put in plenty on the boards the squeak.

No they don't. This could be a Planning matter if the building is listed or in a Conservation Area but of no concern to Building Control.

Yes but should be listed in their quote.

You could get rid of any big nibs and brush some building sand or sharp sand over to take out some of the undulation. DPM lapped up the walls, PIR, polythene then 22mm chipboard with a 15mm expansion gap around. Will be fine for carpet finish.

Mortar is fine.

Worcester and Vaillant are also good.

If you post the refusal notice, which you can anonymise, I am sure you will get some help.

Unless the firm is very local you will have delivery and collection charges so a small mobile crane with operator may be cheaper.