torre

The pull down shutter unit cuts off the corner, makes it a bit unusable (hence the vases in the render maybe). Perhaps if needed put it in the right corner instead? I've found with hindsight that side opening wall unit doors tend to get in the way when open, if have more lift up does next time. Bit of a mix of sizes on that wall. Island hob works well for us, very sociable. Really like the waterfall island.

I'd think about both protecting your site, and protecting the public from the dangers on your site. Sites are exciting places to play, but dangerous. Signs won't keep children out, you need a secure fence for safety.

Best idea is to get a couple more quotes. On the positive side, it's broken down clearly, but looks on the high side to me. Couple of examples - when we had electrics done recently, our electrician would've got that done in a day (two max). Boarding and plastering say 3 - 5 days. Not huge material costs to those either.

Ours was an outside wall so I agree quite significant loss, but we accepted it in the bigger picture of much improved insulation of the other 90% or more of the perimeter and slab. For us, the trade off of extra cost and effort of disrupting existing stairs wasn't worth it. Whether you're living in the property at the time will be another factor.

When we did this, to keep the stairs as is we excavated to the edges and then added an insulated upstand to minimise cold bridging to the rest of the floor. Below our stairs is only cupboard space, if we ever clear it out we'll probably add a layer of rigid insulation and a false floor

Sounds like the surveyor could have explained why much better but I think they're right - Velfac windows are fitted with a shadow gap (10-15mm) and the whole visible frame hinges open. See here The gap is needed to give clearance for the frame to hinge within the opening, so nothing can be installed in front of the frame or they won't be able to open! So, the slips will need to be in place first (and will slightly reduce your openings). A cut edge is a good idea to ensure a consistent gap

On the building regs side, if your build, especially mentioning cladding, is encroaching closer than a meter to the boundary don't be surprised if you need to prove it's non-combustible, prevents spread of fire

Maybe SSE would upgrade your existing supply to three phase at a reasonable cost (versus 21k!) and that might give you more options, like splitting into three single phases? (Bear in mind I'm a light bulb changer and plug wirer, I'm not in the trade!)

Sounds an interesting project, but do you ever intend to sell? Regardless of your engineering experience a secretly built DIY basement with no planning, building control or SE design would be a big red flag for any buyer or surveyor.

@Dunc +1 we did the same calculation - similar conductivity, but the high strength aircrete are much cheaper and easier to install

Is the rad fitted with a thermostatic radiator valve? Sometimes if they've been turned off the pin inside can stick down - you can try taking the control head off so you have see the pin position - with the head off the pin should be raised and you should be able to push it down. If it's stuck down, try (gently!) pulling with some pliers to free it.

There will usually be a condition along the lines of "The development shall be carried out strictly in accordance with the approved plans and drawings" and that allows you to make updates to the plans if you're updating the design

Getting a heat loss survey might be worthwhile, see where the heat is going. Have you weighed up internal versus external? External may initially look more expensive but internal is very disruptive, even room at a time. What would your plans be for handling kitchen and bathrooms? Refitting those will be a big added cost. Both are an (expensive) opportunity to refresh - maybe add a more modern look externally, or a good time to rewire etc internally. We've done internal but only fully renovating an old solid wall property, I'd lean towards external on an 80s bungalow - better insulation, less condensation risk, less disruption, but probably more ££ and less DIY friendly

Looks like you've a gallery landing open to the kitchen space below. Have you looked at the fire safety impact of that? Possibly fire doors on the bedrooms and windows suitable as means of escape.

Potential issues are likely to be around over-development, negative visual impact, highway safety, parking. I'd draw a line following the front line of properties left of pic and try and plan within that, which probably means building closer to your neighbour, planners would probably baulk at anything intruding closer to the corner than that. Is there any negative planning history for the site or nearby? Are you in a conservation area? There's inevitably a fair bit of risk (and cost). What are your plans and particularly what's your plan B if you can't get permission? If you're going to live in one or the other, would you be happy falling back to a large extension or terraced property that wraps around that corner?

Looks a neat job but hard to see building control being happy with slabs up almost to DPC by the render and brickwork. Check what they'll sign off before paying in full. How high is your bifold threshold and how exposed is this elevation? If you end up having to re-lay this an Aco drain would give you better protection from driving rain flooding in from your patio and seems to be a commonly specified detail. (You could experiment with a hose/bucket to hopefully reassure yourself about this)

Pretty sure the geotextile membrane's heavier duty than weed fabric, it needs to keep soil etc out for the lifetime of the soakaway. No fill (if you go for rubble instead of crates you need approx x3 the size of soakaway. What you're looking for is a silt trap before the soakaway (that site's got quite a bit more useful info too, including for a percolation test to establish size if you've not done one)

Hard to say beyond "It depends" as so much can vary. If you can keep spans small and don't have to run a soil pipe far or perpendicular to joists that will help, and be wary of the amount of deflection. I remember seeing in this thread that a 195mm easi joist may work a bit better than a 202mm posi. 225mm is generally easier though as it works with blocks.

Government permitted development advice looks like it'll work to your advantage... Where ground level is not uniform (for example if the ground is sloping), then the ground level is the highest part of the surface of the ground next to the building.) You could apply for a certificate of lawful development to remove any doubt

The first elevation looks pretty close to your image and you've not given a huge budget to evolve other ideas so you may need to temper expectations a bit or give a bit of feedback and budget to evolve the design - @ETC's sketches are a nice start in terms of ideas to build on the original. Personally I'd prefer the hall to be more central to the main rooms (and of course stairs to line up). It sounds like you're not too impressed so far though - cheap is great but not if it means a battle to direct your architect to deliver what you want. In terms of the application, perhaps show the new and old elevations overlaid so it's clear you're not actually going much if any higher at the ridge, and make another attempt to win over the neighbours, telling them how much the new design means to you and why. In person may work better than email.

Not an expert but isn't the effective depth only measured from the inner of the inlet?

Another approach to getting the sizing right is to use formers made to your planned sizes and build the brickwork to them, either timber or pre-made cavity closers (we're considering this to workaround windows with a long lead time causing delays if we wait to measure the built openings). That does mean taking on the risk for getting the opening sizings correct though.

Won't you also need some additional height for flashing where the parapet meets the main wall? Maybe look at alternatives to a parapet if it's too tight - could you create a fall from front to back so that all the water drains to the rear (see pic) or fall towards the front into a hidden gutter without a parapet. (Not an architect by the way!)

Demolition will probably be treated as commencement (google "demolition is commencement for cil" for examples) particularly if mentioned in any conditions, so tread carefully and as @Alan Ambrose says, double check with the local CIL team and get something in writing before you consider going that far.

Did they explain why? You've a long journey ahead with your architect, at this early stage you'd hope they'd be listening to your point of view in an area where you've expertise and experience. For me as a client it's important to know that an architect or builder is going to listen to what I want and, if something really doesn't work, explain why when suggesting another approach.