JohnMo

So do you have suitable air gaps either side of the super foil? You need these sizes of battens either side to get the performance advertised. If you haven't bought or started doing insulation yet, I would use Mineral wool between studs (Rockwool Flexi or Frametherm 32) then full sheets of PIR on top of studs and a small service void batten.

That bloke down the pub, now I understand. At least it's all straight now.

Or just switch off the ASHP and do nothing. He seems to want a cold house. This threads being going on for 2.5 years and nothing changes. He had a cold house then, and still does.

Nothing particularly wrong with multifoil, but it needs to be used correctly and have the correct airspace either side of it, which is often not built-in. I wouldn't use in isolation, but with other insulation. But when you take into account the correct air spaces either side, it doesn't save any space, compared to mineral wool

Is that your main insulation?

If I only paid £70 for all electric I would be well pleased, but living in a cold house and have an angry wife. Not having heating on, causes house temp to be cold, everything becomes damp - funny old thing, all the things @zoothorn describes. Suspect the heat pump could heat the building well, but is never given the chance - £70 bills leave no place to hide, when you have a 9kW heat pump. The heat pump is off more than it's on. I'm running a 4kW heat pump, only pay 15p per kWh and my bills are way more than that.

Heat pumps are fickle things. During the commissioning of our heat pump, I tried various ways of operating, a high fixed flow temp and thermostat and Weather Compensation. Surprising both got a similar CoP, BUT, and it's a big but, the weather compensation had to deliver way less heat energy and used way less energy for the same house temperature. Both tested on very similar outside temp performed over 24 hours. Weather compensation delivered 48kWh and the fixed temperature had to deliver 81kWh. Which is bonkers amounts of heat being delivered. Sounds the perfect place and house to live in! Living with a crap heating system (or mainly rubbish setup and or operating manner I would suspect) that cannot warm your house, all so you could get a free cylinder, you could have bought yourself for £500. Doesn't really matter what house you live in, a steady flow of heat into the place it will get warm, even a stone house. As soon as you switch off the heat source that energy starts to be lost and the rest of the energy trapped within the structure also goes. Leave it long enough the effort to replace the energy becomes an uphill struggle - I suspect your heating system is operating like this. Digging out floor if it's to add UFH then you will adding a further delay in getting heat into the house. If you have a thermostat in the warmest part of the house, you system will go on and off and the cold parts never get warm.

One of the main reasons passivhaus specify 3G is based on comfort. The window internal temperature of 3G being very close to room temperature, so isn't uncomfortable to sit next too. The lower the performance the more uncomfortable they are to be near for long periods with it cold outside. We have a bay window, with floor to ceiling glazed and I sit there quite a lot, it's comfortable whatever the weather is doing outside. Not sure I could do that with 2G.

Sorry I was talking Uw, so frame and glazing (Ug and Uf).

You need a really good frame, or a good one and Krypton gas filled.

Or don't do a cavity at all, and do externally or internally insulated.

I've done both, woodcrete ICF is a good hydrophilic material I believe, but good airtightness and MVHR to capture any ventilation heat losses.

I waited until I had a skip full of stuff, off cuts of insulation, plasterboard and general building stuff.

Does your house leak air quite badly? Old houses don't need additional ventilation if the have the fire places still there, they move air at a high rate. Gets back to the point made by @SimonD that airtight houses have better control of passive stack ventilation than a leaky house, where flows can be very high

Can you get it to do a taper charge, so backs off the 10% or so of the charge period

Then ask it the same question tomorrow, and you may get the polar opposite answer

Building control, via a completion certificate. While building and site is under planning permission and the agreed scope of works, permitted development isn't lawful. Substantially complete as mentioned @SBMS, no idea where that comes from. Extending that, you add an extension to a new house before it's complete, sure that's not allowed!

Zero benefit having a battery except for PV offsetting. I'm on Cosy and battery gets charged 3x a day so all my electricity is cheap rate 24/7. I would just get a decent tariff that pays export and allows cheap rates. Move supplier if you need too

The bend supports are just that, depending on what pipe you are using it may be helpful to use them. With something like Pert-al-Pert, which forms its own bend they may not be needed. If you want to add something, some flexible electric conduit could sleeve the pipes, 20mm conduit should be ok.

So where does it say that in black and white?

Plus structural engineer says NO. Interesting product, but if the structural engineer isn't onboard, how do you have a structural design certificate, that worth even the paper its written on? Have a structural engineer says YES, fill your boots, so to speak

No one could answer your questions without more information. Ideally your wall build-up drawings are needed, but you sound like you don't have the drawings down to a detailed enough spec, to even consider buying let alone building yet.

Would suspect it's down to the wall to window ratio and that will vary by room and by house. Example Our living room has nearly 30m2 of glazing and about 10m2 of external wall in total. So going for high performance 3G wins the day, every day. For clarity our living room has more heat loss than the rest of the house in total. So we upgraded to to 3G. I's all a balancing act something's make sense in one build and no sense in another. Generalising is choice decision.

So elaborate! Not exactly correct - the heating demand rate if 10W per m² max demand is a good indicator that us incorrect. That number being chosen for a specific reason - a heating element in the MVHR (flowing at passivhaus flow rates) can supply that heat without getting a burning dust smell from the ventilation air. A passivhaus still needs heat not much, but some, you don't need a huge gas or oil boiler though.

In Scotland mechanical ventilation become mandatory when airtightness gets better than 5m3/m2. So with a decent airtightness I would worry (like the other half) about piss poor ventilation. For the sake of a small cost in running install dMEV fans or a MEV system