Mr Punter

Cement board is a pain to cut and tile adhesive sticks to it so well you may need to smash the boards the remove the adhesive. At least with plasterboard it just turns to sog. I quite like the idea of the Wedi board type stuff which is lightweight and waterproof. Not used it though.

If you have a pump station, do the run in 90mm black MDPE. Run it in the same trench as your other services. Convert to 110mm brown pipe to a new chamber and gravity pipe to the sewer / final chamber. If you have a high or variable water table, the pump station chamber needs encasing in concrete.

I thought this may be the case. A bit of a pain under thin tiles. Not much sticks to DPC very well.

You may want to use a mortar resin or a strong mix in a pointing gun if you chase the joints out. Make sure you vacuum them first. An apt user name!

Your ledger board will restrain the walls better. With the masonry hangers would you be chasing out some of the mortar join?

Would decent tile adhesive give a better bond? When the bond fails with tiles, it tends to be on either the tile or the substrate, which is why they are often best primed / back buttered.

Does that include for labourer for loading out, mixing and distributing mortar etc?

I have had factory fitted insulation and it does not look like the site fitted stuff. A very tight fit and clean cut edges.

However you slice it you should not excavate by machine without hand dig first to expose the water main.

I have done some flat conversions and just did PCC. It was acceptable to all 6 buyers / their lenders and much cheaper than NHBC, who had not appetite for conversions. CML give a list of lenders who will accept a PPC. Not worth the paper they are not written on if you ever wanted to claim, but then structural warranties are not a lot of use either.

Timber shrinks a lot across the width, so sole plates, top plates, locating plates and top and bottom of frame sections, together with floor joists, mean you need to allow for about 5mm for the ground floor plus 10-15mm for each additional floor. This can impact cills, heads, soffits, roof, and soil pipes. Compriband (Illbruck) is often used to seal around windows. Just bear in mind the direction of shrinkage when making the allowances.

All looks very well thought through and a good use of space. I like to see storage in all the bedrooms but it looks like it they could all accommodate a bit. The bathroom extracts are best placed in the middle of the shower, although you won't die if they are left as is. Was MVHR too impractical to incorporate?

If the 11m2 is just for a more habitable site office you could insulated and then cover with floating chipboard floor. 10 sheets will cost £100 and easy to lay.

Another dream crushing NO here I am afraid. Rainwater that is collected is best done in a water butt and used for watering the garden. Even then they can sometimes cause issues.

The 300mu is 1200 gauge so will be fine for DPM. 125mu is 500 gauge and fine for the separation layer.

Hello and welcome. I am in Sussex too. What are you building?

You can mix normal sand cement screed in a mixer so it is just moist. Laying it takes a lot of skill. I would not attempt this myself but please let us know how you get on.

Plastering is messy so do that first. Also if you have UFH you can get the manifold onto a finished wall.

Draw a plan to scale so it is easier to work out quantities. Use an engineer to spec the steel. They should be cheap. Get a quote first. You can just brush in sand cement slurry to the beam and block to lock it all together. Lay the slabs on them into mortar or a sharp sand / cement screed. I would not want to tie the steel to the house but your engineer may have a suggestion. You don't want the concrete beams more than 3.5m or you will not move them. Even then you will need a helper and some Weetabix. My preference would be a wall at the front and back to support the concrete beams. You could have storage underneath.

I find old saws good for insulation and plastic drainage pipe.

If you are doing a multi unit scheme (2 or more), Openreach have a developer portal. I took me 3 months to register online because their system was so crappy, but this was the only way I could get job looked at.

Make sure you get the panels with the curved tops. The welded top ones crap themselves if you look at them funny.

Thanks @Onoff and @TonyT. I went for MK boards with surge protection and 2 x type A RCDs in the end. Cost an extra £430 over the 8 flats but hopefully more future proof.

These would be a start

The link just gave delivery. I was looking at swapping for these https://www.screwfix.com/p/british-general-12-module-6-way-populated-high-integrity-dual-rcd-consumer-unit/4674g The wiring is fairly new and there are 8 small flats in the building.