Conor

Depends entirely on what loading will go in to the loft. Also, definitely want stilts to avoid compressing the insulation.

Our BCO didn't care about second fix electrics, as long as cables either isolated or terminated..so fire on and get first fix done and do the minimum second fix as you need. Obviously your interconnected smoke alarms have to be working throughout.

Is the screed fully dried out? Have you tried simple watered down PVA? You'll need to do something with edges / expansion points. We've left our basement as bare cemfloor, and it's crumbling and cracking at door thresholds etc where it meets the foam perimeter.

If you've moved in, and the building is habitable, then as far as LPS are concerned, it's a completed house. BC separate. They visited us in March just after we moved in, we didn't get BC signoff until July. They don't issue you anything and has no real impact other than you have to pay rates. Just be happy you're not in North Down 😂

I've done exactly this with my shipping container, used VP300 roofing underlay, for roof and sides to keep water off the external insulation.

Run two battens along the top, that's how we did it with our EPS roof panels.

Don't have it to hand but my GRP supplier supplied a silicone type stuff in tubes for movement areas. Used it where deck abutted steel and would be thermal movement. Stuck trim over the junctions and top coat over. No issues so far.

This is a question for your structural engineer, nobody else. Most likely OK, but you've no other way of knowing unless somebody does the calcs.

Any SE should be able to do the job, ICF is really just a form of concrete shuttering.

Most of the local suppliers I used delivered for free, or a nominal amount. Barley used my trailer, even.

Pm me the map and I'll see what could be found on site.

Topo survey won't locate a water pipe. Need to contact UE... Unlikely they'll help and you might need to do some trial pits. Worth have a Topo anyway. But do things in right order. Speak to an architect first, then think about ground investigations.

As side of reducing visibility at the junction, your LPA might view that area as public amenity space and not want you to close it off. There might be a bit of paper hidden somewhere that has restrictions on it. You won't know until you do it and somebody complains!

Dropped the whole lot down

Ours was on the first floor, but same principle, we shuttered off the area with timber. This meant a 100mm deep recess for the bath to sit in. Having the bath 100mm lower than then floor level makes it easier to get in and out of. Highly recommended.