Mr Punter

The top layout is 36m2, the lower is 64m2. Timber frame with blockwork skin would work OK and not too expensive. You would need building regs.

Maybe the shower could connect to the stack separately. The WC flush may pull the shower trap as configured.

18mm OSB should not sag if correctly installed on 400 centre joists / firrings. If the boards are defective, they need replacing. The grp is there as a waterproofing layer, not to make up for dodgy OSB.

Do you have damp in the floor, the walls or both? Where is the external ground level in relation to the inside floor? Have you checked for any possible leaking drains, gutters and pipes? I have seen the silicone rods and they seem a cleaner way of installing a DPC than the liquid, where it was hard to adjust dosage etc. Did yours fail? If so, did you follow the manufacturers instructions?

SIPS OSB I assume.

18mm OSB or chipboard t & g, edges glued together. Leave a gap of 10mm around the edges for expansion.

Half the diameter.

I would use 50mm galvanised coach screws with a galv washer.

Well done for doing the test. Ask the manufacturer why it does not perform correctly. Let us know what they say. They were top of my search results. I would hope they are not diverting the money intended to create a decent product to advertising.

I have had Weber LAC applied with mesh in the past. 2 costs is about 5mil and you can just sponge finish and paint.

For several years we have holidayed in a villa in Portugal. They had microcement and I saw many areas fail at considerable expense to the owner. It looked great at the outset. I would go with tiles.

The mesh looks fine. It won't hurt at all if this is left for another 3 weeks before you pour. It would be best if you have decent contractors to do this, but it won't fall down if you don't. Setting a target of having the concrete as the finished surface makes this far more prone to failure. Concrete is not a very attractive finish. A 30mm latex screed over will be flatter than any pancake.

Would you please straighten up the picture of the stag?

Will your main contractor take on the timber frame risk (for an additional fee)? If you start purchasing materials and / or employing sub contractors you will need your own insurance.

The bit where you have "infill with subsoil" is now concrete. Do you intend to get rid of this? I think that without steps, the slope will be too steep and the lower section of garden will be fairly redundant. Gabions may have been better to retain the patio, but that ship appears to have sailed. If you don't want handrail you could have some planting at the top.

Install air con. It will be free to run during the day.

Lay the pipe as shallow as possible. You can go to 1:110 so your 30m run would have about 275mm fall. If invert at the start is -250mm, this will give an invert at the soakaway of -525mm assuming ground is level at 0mm.

Fix some temporary vertical battens near the corners with masonry screws.

Bear in mind that as soon as you serve a Party Wall notice you will be liable for the fees of your surveyor plus those of the adjoining owner. In any case you will be liable for any damage. If you do the work without serving a notice the only recourse the adjoining owner has is to issue a High Court injunction. If they are not successful with the injunction they will be liable for your fees and expenses in defending it so quite a gamble if they are not sure of winning.

As long as the screen is in OK and the door works it is fine.

Looks OK to me.

So are others suggesting that with, say, joists at 600 centres it would be acceptable to have no noggins at the board ends? So one end of the board could be unsupported for 500mm, just relying on a glued joint to hold up for an indefinite period? IMO it is not a massive risk but I would rather not take it, especially if the joists are at 600. 400 probably not so bad.

Yes they are taking the mick, but 2 weeks extra hire can't be more than £200. Too late now, just give them a bollocking.

A few people here have done thick wall timber frame and I beam roof, all with blown cellulose insulation. Apparently really good at external sound attenuation, as well as thermal insulation.

Use an eaves tray at the bottom. Sort ventilation and fascia / soffit details. Fit the membrane then nail the battens and counter battens using 90mm Paslode galvanised nails. Use an eaves tray at the bottom. Sort ventilation and fascia / soffit details.