Mr Punter

Something wrong there. If the system is balance the intake and exhaust air flows should be about the same. Is the building occupied and up to temperature with the heating on?

I agree. I think that this should be covered in the regs and some minimum standard applied. I know several people who get a new kitchen, a bit of building work (like chimney out) and underfloor heating with little / no insulation. The problem is the hassle and expense of taking up an existing floor, which neither the builder nor the householder wants to do. If it costs an extra hundred a year to heat, they may never get their money back.

What a waste of materials if it has to come up. They normally start with a perimeter upstand of insulation that slows heat transfer to the walls and allows expansion in the screed. I can see why it will be difficult to liquid screed. Could they use a solid overlay like ScreedBoard 20? It can be tiled and is a dry application that you could even DIY.

Your supplier is badly reviewed. If your flat is on the ground floor, most of the heat will go straight into the ground. There is an aim around the world to reduce C02 emissions and your proposal is doing the opposite, by heating up a large conductive area in direct contact with the ground. I appreciate there are no simple solutions for this but 6mm insulation is not going to do much. At least go for the overlay boards suggested by @PeterW. Most people here doing new build would suggest at least 100mm of high performance insulation for UFH. Can you take a bit off the bottom of the doors?

If you don't like it and they won't remedy it, issue proceedings. Not great that you were down to do the internals.

But they are Chinese crap. At least buy European crap.

I have a Samsung fridge freezer with extended guarantee. Lucky as it has gone wrong 3 times in 2 years. Engineer due back out for yet another fault. They are poor quality design and build.

Never going to happen. Compared to a wall string, a template will be far worse. Why mount a template on the wall drill holes, and fix treads individually when you can just mount a wall string and job done?

I think having the string fabricated with the stairs is probably easier to get right. Mounting the treads individually would be more likely to fail structurally and be slightly misaligned. The tiles provide an excellent finish. A small slip when over-refreshed looks like it could be painful.

Now there is a task I would not fancy taking on! Can you keep us updated with progress?

Unless it is going to a foul or combined sewer it will be unsuitable. Grey water is not contaminated with poo. Please make sure as surface water is often discharged directly to rivers, the sea, feed drinking water reservoirs etc.

Have a look at https://www.pavingexpert.com/ceramic_01 If you are having a pool, make sure the paving is non-slip.

I think the fact that it is split horizontally with the materials will mean that your eye will not be drawn to the verticals. I think it looks fine.

I used the Brett Martin placcy cast iron on a project but not sure it was worth the extra: I quite like the Guttercrest ali stuff we did below: Next project will be grey plastic.

Water companies often fit small bore meters as standard. Apparently they are better at recording low flows. If you want a higher flow / larger pipe without the restriction at the meter they often have a much higher standing charge. If you need a sprinkler supply, have it as a separate pipe. Our water company like to fit a meter to these as well, just to make sure you are not nicking their water or leaking. In this case it is well worth specifying a large meter to guarantee flow rate. Fire supplies do no have a standing charge.

Exactly. You do this by way of a transfer with the land registry. You can't transfer land you own to yourself. You will transfer the existing house to a new owner and retain the plot for the new house.

It is almost pony paddock size so maybe that is how it will be used.

I really would try hard to get a gravity connection. Failing that, a small pump station. I would rather people crapped in the garden than have a Saniflo.

I quite like the single storey bit giving a good balance between living and bedroom space. I don't quite get the elevations but maybe it will be fine when completed. I think I would want to see a 3d render before I committed to this.

To provide an opinion on what may be the best route you would need to give facts and figures. You need an approximate build cost and sale value on the new properties. If you estimate the fully inclusive build cost at £2,750 per m2 plus extra over (£50k?) for e.g underpinning it will give you a start point. For sale values, these should be in line per m2 with those in your area. Deduct the build cost from the sale value and that will give an approximate profit. Assuming you are able to create a couple of 90m2 houses, total build cost £545,000. Your sale prices could range between £300,000 and £1,500,000 each. Perhaps they would value at £450,000 each, so £900,000. From the £355,000 you would need to deduct CIL, sale costs (if you choose to sell) and any other taxes that apply. A developer might offer £220,000 for the site with planning or option. Whether you are a partnership, ltd co or LLP, if you don't intend to sell, CGT will not be an issue and VAT will not be charged in full if you use a main contractor. CIL will be charged whatever.

Don't forget wiring for speakers, ethernet, TV, kettle, toaster, coffee machine, radio etc. Also you may want side tables near the sofa for drinks, nibbles books. What happened to the laundry? I like the shelves. Is it a kit? What software did you use for the drawing? Nice project. Lots of work to achieve this! Can you keep us up-to-date with progress?

You have obviously looked long and hard and come up with something that you like and I am sure it will work. The fridge freezer / oven is not optimal but they are both built in so also have a couple of layers of chipboard to separate. The oven is probably not on for more than half an hour a day on average. Very pretty plans and elevations!

Good that you have the engineer visiting. Have you dug a trial hole to expose the existing foundation right to the base?

Good news is there should not be any CIL and if you demolish you should get the VAT back. The stair being open plan may be an issue with building regs fire and also sound and kitchen smells going upstairs, which I would not want in a larger house. If it is what you want and the layout suits, go for it. Personally I like that there is some separation between the kitchen dining and the lounge. It will be interesting to see how this scheme looks externally. Only you know what works for you.

Is this a knock down and rebuild? If so, it would be nicer not to have sloping ceilings throughout the first floor. When I looked at this earlier it seemed like you could achieve £5k per metre. If you budget 2.5k build costs you may arrive at the ideal size property. I have only ever made the sums work out when demolishing 1 and building 3 but I have to make a living from this.