Conor

I've a 43" TV fitted to plasterboard using Fischer plugs. You don't need much if they are flat mounted.

If I were to pull any weak points from that list it would be the walls and windows. I'm not sure if 90mm insualtion gives you 0.18 anyway unless you've something else going on. Aim for 0.15. And for windows, definitely triple. Ours average at 0.8, some are 0.5 (a 40mm thick, 2x2.4m unit), and not that expensive in overall scheme of things. About the same as kitchen and bathrooms combined.

Look for a local saw mill / lumber. Will be fraction of the price of a online shop or builders yard. They'll cut and plane to your spec if it's not an off the shelf item.

Different banks have different requirements. Ours, was architects completion certificate and building control signoff. But ultimately, it'll come down to the banks valuation surveyor's opinion. We recently went back to our bank for additional money but the valuer rated the house as "zero" due to unfinished landscaping and a few other things.

Compact foam replaces traditional concrete door blocks. I fixed mine on to the concrete slab with 150mm concrete screws. My DPC detail was a bit different, brought it up and OVER the CF block, rather than under it in that detail. On that detail the threaded bars in to the end of the slab transfer the loads.

Ashp fine for getting hot water. We've ours set to 45c and don't need it any hotter. You just need a big enough tank. Also great piece of mind with young kids in the house and no risk of scalding. A couple towel rads on the top floor run by the ashp will do the job - no need to any direct electric heating anywhere. We put UFH in anyway as we've concrete beam floors and screed... No brainer to put the UFH as costs were minimal. Three towel rads still sitting in their boxes! As others have said, get a detailed heatloss analysis done and take it from there. You'll end up looking at a 5-9kW heatpump. We're 315m², three story and out 9kW heatpump does the job well. No way you'll need a 12kW.

Our build was ICF so basically no upstand needed. The screed company insisted on the foam perimeter strip as said EPS wasn't compressible enough. I'd assume same applies to PIR.

Wrap in foil backed mineral wool insulation. Tape joins with aluminium tape. Not the nicest job in the world

If the sewer is adopted, it would be UE who you'd apply to and would need to maintain access. I assume you own the land? I don't rate your chances to be very high, but you can only try! Diversion possible but you'd need neighbouring landowner to agree and new wayleaves established. This will take >6months.

If you've mesh it'll be fine.

Actually, if the primary driver is drying, get some cheap dehumidifiers and just leave them run. They kick out a bit of heat as well. More efficient and effective than space heating. We bought 5 from Screwfix for about £120 and sold them on a year later for about £90 each.

Wtf? Leave the coils outside, measure up each run individually and cut each length as needed + ~2m

Cheap dehumidifier from Screwfix.

For that kind of work, standard "carcassing" timber in 3x2 is sufficient and a good bit cheaper than CLS. Go to your local builders merchant and they'll know what to give you. If you need extra strength, line one of the sides with 18mm PLY.

Yeah, your buffer should have a 3kW immersion in it, and if not can be easily fitted. You can then simply turn it on, turn the thermostat down to about 40 then just set your pumps on. If not, we used 1.5kW blow heaters - one on each floor timed to run overnight. Worked a treat and cost about £100 for the month or so they were running, along with a couple dehumidifiers.

Second the ply box idea. Let it sit about 40mm proud and then template another strip of ply on the outer surface of the ply box to hide the gaps to the block. Kinda like a rebate. I did this with a box for a hidden toilet cistern cover and worked well. You just then seal up the ~2mm gap that's left. Either use marine ply or varnish/PVA seal normal ply.

Need to insulate all runs in the uninsulated attic Not sure what you mean by "repurpose" the existing bathroom extract but you want to start with all new ducts and plenums / air valves. Keep the kitchen extract a couple metres away from the hob and place in such away to encourage airflow away from the other spaces - e.g. towards point 1. Double up the airflow from the extract kitchen to balance the system. You might want to run two ducts to this. For external ducts, you want these to be as short as possible and for the vents themselves to be about 2m apart.

In winter, walls and windows of the house will be colder than this, you feel this through the slight conventions and radiant heat loss. There's a setting in the neostat where you can change the start / off points. Default is something like 1.5c, change it to 0.5.,

You need gully traps on both of those before the 110mm pvc. And orange pvc pipe has to be fully buried as it's not UV stable. And do your drainage plans allow you do discharge directly to a watercourse without attenuation? In reality, the way you've done it will be fine, bar the odd blockage you might have to deal with in autumn. But if this is works involving BC, it'll fail.

Id allow £2k/m² for the new bits plus £1k for the rest of the house. Think you're looking in the £300k ballpark. Budget kitchens and bathrooms etc will go someway to keep this lower, but hard to reduce the core construction costs.

You got your ducts connected up correctly? I.e. you're not just pulling exhaust air back in?

You could in reality get away with just hammering the rebar in to 16mm holes, I've done this several times and with a 200mm deep hole, those bars aren't going anywhere, esp as they are to stop differential movement, not pulling restraint. Check with your SE.. tho they will almost certainly say hilti resin.

No reason why a small number of storage rads and a small DHW cylinder all running off-peak wouldn't do the job. BUT be mindful that for mortgage valuation and resale, a house with no central heating can still be an issue for some. AND you say "approach" passive house standards. Quite different from hitting them. We are the same and even exceed the min U values in most places... but would not be without our ASHP & UFH. But we did successfully heat the house in its first couple months with a couple dehumidifiers and a fan heaters. Still, can't beat the convenience of UFH that costs pennies to run.

Our rooms are all 20-21c. No complaints. Light summer douvets all year round. Stop overthink it.

Interested in this as well, we got three of the damn things, the elements are ment to be hardwired in to a fused spur and left on 24x7. Haha.