Mr Punter

If you can, sink a mini pump station in, that would be best. They have a high level alarm. The outgoing pipework is pressurised and often 2" diameter. It connects into the 110mm pipework. Get one that pumps solids, not a macerator. Avoid Saniflo like the plague.

An insulated concrete floor may work much better than timber. You don't need any airflow underneath and there is no risk of rot.

Hi @Mike W and welcome. I am fairly near you and have had a few properties in B & H. Is yours a Victorian terrace with painted render? What are the plans to improve energy performance?

Contact your insurance company, tell them what work you are having done and ask them to confirm if you are still insured. Often if you are not living at the property you may need a special policy but again, ask them to clarify.

I think your original plan was fine, but you can ditch the heating upstairs. Maybe an electric towel radiator or 2. I am not sure why you need cooling at all. If you have solar gain issues, try to design these out. If there is a problem room, you could install a split a/c unit. They are cheap and pretty efficient.

Yes, lag all the hot pipes. You may also want to undo some of the clips so you can get thicker insulation around. Lag the cold pipes too if you are really bored.

Yes and according to my tilers the tiles need to be really flat. Try pairing them back-to-back and front-to-front to test this. If they are a bit out they will be better if you reduce to, say 1/4 bond stagger. I have heard good reports of tile levelling systems which you may want to look at.

Carry on with your own household insurance and make sure the builder has a contractors all risks cover or similar.

I quite like external wall insulation as it wraps the whole house in a tea cosy. You can take it down below ground if it is EPS. Neither of your quotes sound like external, just internal plasterboard / PIR laminate. Make sure you are comparing like for like.

I have used Weber LAC base coat with a fabric mesh. Base coat rubbed up to a sand grain finish and then masonry paint. Worked a treat and still good 10 years on.

You need to be within 600mm for it to work properly. You also need to keep the nozzle a uniform distance from the what you are painting. The sprayers need lots of prep and cleanup. Any lumps in the paint are a no-no. If the surface is good, the finish is excellent, but you cannot touch in any mess-ups without it showing.

Did you get a price to build your proposed house. Given values in your area it may be a better option to do as large a 2 storey rear extension as you can - a bit like at no. 14.

With 400mm v 600mm centres the actual percentage timber will not be much more. Loads of timber is in double studs at openings, corners, top and bottom rails, sole plates, top plates and locating plates. It will make more of a difference on a long wall with no openings but this is not typical in a house.

I have not seen this anywhere before and have been an NHBC registered builder. The internal partitions will shrink at the same rate as external. Also, some internal walls are structural so you could not install the roof. Could you provide a link as this seems to be nonsense?

Nice project. Can you post up the building regs drawings and spec? I would be really interested in how it all works.

If they take full responsibility it is probably worth paying for, otherwise you can get into a blame game, where it is not established if issues are down to the manufacturer or the installer. Getting an all inclusive price for survey, design, manufacture, preparing openings, delivery, offloading and distribution around site, installation, sealing and sills would be valuable for the de-risking. Better if backed with a decent guarantee.

Composite doors are low maintenance and look a bit better than upvc

Nice. I hate doing ceilings with Rockwool as I always get a bit down my back, a bit in my eyes and then inhale the rest.

I quite like the untreated timber on @tonyshouse. If it is Canadian western red cedar, it is really pricey to buy

I have used wax to fill a few gaps that have opened up with picture framing around oak flooring. If you use wax, get the OSMO oil on first or it won't take where the wax has been applied (only a fool would do otherwise!).

If it is a new build they will be bound by the Consumer Code for newbuild homes https://consumercode.co.uk/

Also, if you have not exchanged contracts you do not have to go ahead. They must refund any deposit you have paid. If you have exchanged, there is often a long stop date by which time the building must be ready or, again, you can pull out.

We have a separate 50mm supply for sprinklers and it has its own meter to check water is not used. They don't raise any bill for this. A small amount of usage happens if the sprinkler flow rates get tested.

My take is if you want it to be permanent habitable space you need building regs. Home office / studio / garden room you will not. If you have any fixed heating you would need regs.

@WillShields why are you using Fermacell? I suggest a trial just getting a few boards and doing one small room. If that goes OK, then go for it. Not for the fainthearted. 250 boards my goodness...