Mr Punter

Like something out of Mad Max. Not sure I would lift a pack of blocks like in the last pic without a change of underwear nearby. Let us know how fast you can drive it!

Agree with @PeterW about the shower. We have one that is 1800 x 700 and it is a bit cramped. Can you have the sink and WC on the same wall?

Room dims might help. Can you add them to the drawing, or will that spoil it?

You would need to do all the ducting and room terminals plus electrics and condense drain but you could leave buying the unit until later.

If there is a screen or panel to the shower don't go less than 600mm. Is there a WC in the far corner? If this is an en-suite maybe used in darkness the layout may need a rethink.

Cut a piece of OSB bigger than the infill and screw it to the face. It lasts a surprisingly long time.

Three on the inner course seems excessive, especially with the cladding. I think you can send the drawings to Visqueen and see what they suggest (normally fairly OTT though).

Hi @Alan and welcome. Before your architect does their detail drawings, make 100% sure that your warranty provider and building control are happy with an ICF basement.

I have had some fantastic sound test results on timber frame party walls. Even the standard Robust Detail gives fairly good results.

If it is just that wall, would it be out of the question to clad it? Could use oak, clay tiles or natural slate?

Can you not have a window mounted fan, as the window can be set into the wall a little. If the window is inward opening you could access the fan for servicing or replacement.

Build the wall in 140mm blocks. They are better if you need to cut deep chases as well.

If the site is within the settlement boundary and house prices in the area are over £3500 per m2 it may be worth demolishing the existing buildings and gaining consent for, say, four new houses.

Bear in mind that plywood is often 1220 x 2440. If you can get it metric sized it will save a trim-up.

I have seen this happen a fair bit in France. Much better results than trying to fix something which is inherently defective.

It is really difficult to get it to fit as sometimes the studs are a bit thin or the boards are thick. Use 130mm or you will struggle to get the plasterboard on.

Making this a u shape means you have a very high external wall to floor ratio so no chance of it being very energy efficient. It also complicates the roof design.

Check with your warranty provider and building inspector for the required spec. Flat roofs are a big source of claims. There is no standard covering for flat roof. Can be felt, single ply (lots of types), liquid, fibreglass or GRP. It may be easiest to have thin deck on your joists, then firrings to fall direct to outlets (no box gutter), thin deck and insulation then deck to take the waterproofing.

Will smoke from the BBQ not blow into the house?

Perhaps look at reducing the number of dormers and increase their size. The one that cuts through the floor zone looks a bit odd. Could you add windows to the gable ends?

If you have a parapet all round you must have 2 outlets. Why not scrap the box gutter and just direct the roof fall to the outlets? What is the proposed roof waterproofing?

Can youpost a site plan showing the road and neighbouring properties?

Sometimes you have to double up or use a glulam or two. The 5.4 is a fair span.

Make the house airtight and well insulated - especially the ground floor - and add MVHR and the space heating costs can be reduced to the point where ASHP v gas will make little cost difference. The gas boiler / heat pump can be swapped later but the insulation / airtightness / ventilation is a far bigger job. A single ASHP should be fine for both floors.

Before you make the final decision, bear in mind that Trespa is one of the cladding types being removed from high rise due to flammability and although this will not apply to your project, insurers are very risk averse and may change their criteria in future. The oak frame garages often have brickwork to the lower section and oak cladding above, with clay roof tiles. You could also look at slate. If you want to convert it in future make sure you buy one designed for this. There are loads of companies who manufacture and supply the kit. Sometimes it is worth giving a few a call and having a chat, as you do not always get the information you are after from their websites alone.