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Forget fitting any additional insulation it is 100% not needed, forget the u value of nudura blocks for some reason it just looks poor on paper, they don’t add additional insulation in Canada you certainly won’t need it. you will wonder why you fitted a heating system at all once you move in, sort the airtightness and heating will be the least of your worries.

Airtightness will trump insulation, and in winter, that, coupled with MVHR, will give you a plenty healthy-enough ROI on the house you've built, and then live in. Adding IWI will be expensive, hard to execute perfectly (to achieve that 'goal'), and will impact on 2nd fix and GIA. Leave it alone, you'll be spending a grand to save a hundred. Pointless (in actual, real life).

Have you asked the roof panel manufacturer?

I always thought it was fascia, but I'm definitely guilty of forgetting the 's' - it's one of a few words I have to consciously think about! 🤣 I think because the ply is structural, it needs to be screwed directly to the rafters - I did ask the SE about a few options but he wasn't keen. Massively wasteful too as all the joints need to be staggered. Yes, absolutely - that has been planned in. There is a 50mm gap below the ply, then insulation. At the eaves I'll add a vent strip in the soffit and at the top there is a Glidevale Monovent specified by the architect which takes up a load of space below the windows and ultimately forced me to use a lower pitch than I could have had otherwise. I just need to work out the best approach to ventilating that space above and below the Velux windows. Ah, I didn't know - I've just found a few helpful resources relating to roofing in Scotland. I don't particularly want to change too much at the moment, I'm just trying to find a build-up that will actually work and satisfy building control. I was hoping to use a roofing contractor for this aspect, but as soon as they hear about the ply they're not interested as it's unconventional. Just received a labour-only quote from a good roofer I've used before for £6K - it sounds like a 'go away' price to me so I will probably end up doing this myself.

Have you asked the roof panel manufacturer?

My hydraulic design in case it’s useful. 100% possible. Find a certified Panasonic installer and your installer would do as mine did and defer to Panasonic technical to do the design. They just install. If it’s wrong it’s on Panasonic so as long as they follow the schematic they are covered.

We fitted 100mm EPS on the outside to get our standard amvic blocks to 0.15. it's a LOT of work!!! But relatively easy. If you do PIR inside, you lose space and make fitting plasterboard more problematic - no guide lines for screws and screws will have to be something like 100mm+ We never did a service void, spark was happy to chase out with a hot wire cutter. Nothing else is really run in the external walls

as JohnMo said with the hydraulic design pretty much but I wanted true cooling so I went fancoils so I can run at proper ac temperatures. I’ve installed this exact setup with a Panasonic aquarea tcap heat pump. Ground floor is UFH and first (and second floors) are 7x fancoils. All pipework lagged and all fancoils have condensate drains. It took a while to get the design how I wanted it and warrantied with Panasonic. I had an extra towel rail loop that they wanted to make sure was isolated from chilled water so that’s why I couldn’t go off their standard design. I can run 5 degree water in cooling mode to the fancoils and keep the UFH loop at above dew point (16 degree) as the Panasonic accepts a dual zone temperature control. It’s critical that the heat pump controller actually supports this and Panasonic was one of the few that I found that was big, reputable and would warrant the hydraulic design. I worked with their technical design team to get the design right. it fundamentally works by having two circuits off the buffer (sorry but yes, Panasonic mandate a buffer for hydraulic separation in this system design). In cooling mode, heat pump can chill the buffer to 5 degrees. That loop is pumped straight to any FCUs that demand cooling. The second loop to the UFH has an inline temperature sensor and a 3 way mixing valve. The temperature sensor connects back to the heat pump controller and that makes sure that water leaving to that circuit is blended up with return water to a safe minimum temperature. If the circuit stabilises at say 16 degrees the zone valve closes to prevent the circuit going any colder. it’s a pretty simple setup really. I had additional complexity because the towel radiators are on the same circuit as UFH. There’s a zone valve I installed before this circuit that is controlled by loxone relay so in summer I just deactivate this. You could Do this with a heating controller as well (or a switch!).

Not got it yet, but I really am hoping for 0.5. The windows and most doors are Norrsken P31A which are capable of it apparently. The roof is a monopitch warm roof that has minimal opportunity for leakage. We'd said that if we don't hit our desired ACH that we'd consider Aerobarrier. I'm not planning to let that make me lazy though!

That last photo looking up doesnt look great to me, the new wood looks very close, im no expert though. I have had our linner catch fire before and it generates a lot of heat. Could you cut back the drylinning around the fireplace ?

Bum steer..... What's your AT score, or target AT score?

He doesn't want flat ceilings!

No, my build was spec'd in 2021 using their standard blocks. They advised us at the time not to bother with anything other than standard.

All glass absorbs some solar gain so standard 3G is always going to have less solar gain than standard 2G. So 2g with solar glazing makes no sense to me as the solar gain% on 2G with solar glass is probably about the same as 3G but just colder in the winter. If you really want a roof light with low G then the velux passive has 5 panes (now mostly discontinued) of standard glass and so the G factor of just 35%. . For the slider, look at 3G with SKN 176 solar glass. This is what we have on our big kitchen slider and it is amazing. It looks exactly the same as standard glazing but is way cooler. Solar gain factor, as percentage of the heat that gets through is typically: Standard 2G = 65%, Standard 3G = 50% 3G + SKN176 = 35%. New velux with solar glass coating = 29%. 3G all the way, more panes the better, and SKN176/other solar coating where it is needed.

Do you not have the XR35 block?

Our Architect drew a 50mm "Service Void". Now, I know it's not strictly needed with the ability to chase stuff in to the Polystyrene, but what have you done? We have a Posi FF and roof, so plenty of service scope there. I haven't got my mind off running an internal skin of PIR (25/50mm) instead in an attempt to lift the "weak" 0.24 u-value of the Nudura blocks, but I wouldn't do both the PIR and the void.

This bit was very interesting. One thing that struck me, reading this, is that electrons aren't sweet or sour. They aren't dry or wet. Your car or heatpump will run just as well on electricity from a coal plant as a wind turbine as a nuclear plant. Again though the point regarding the UK North sea is that it still won't make much difference to any of the metrics CO2, energy prices, energy security. At least as long as the gas is extracted by private businesses and sold on the international market. *If* we are taking about some sort of nationalised gas company that extracts the gas and provides it exclusively for UK requirements (either electricity, domestic heating and/or industrial use) *then* there may well be benefits in those areas - particularly energy prices and security. However I am 99% sure the above is not what the lobbyists pushing for more North sea drilling have in mind....

Occasionally condensation is predicted eg masonry cavity walls & warm flat roofs with built-up felt or single ply membrane. It is then down to the designer to assess the risk - the amount of condensate, does it all dry when conditions allow, adjacent moisture sensitive material etc. BS 5250 and BS 6229 give guidance,

Or do a proper Scottish roof. With sarking boards and small gaps between them. Then you can full fill insulation with a breather membrane. Do slate instead of tiles and don't need battens either. Using ply isn't really Scottish roof. It's just ply on a roof.

If doing single storey, I would still say a decent pitch on the roof and for the small extra cost built the roof using attic trusses, so you have the option to convert the loft space later of your needs change.

Afraid so, it is just the little one in the photo. I bought it second hand, so just a cheapy (£120), so a different stove might be an option. Thanks

Thanks @JohnMo that's really helpful. I'm thinking mine will be around 110sqm with a lean to of around 9sqm for the plant room/mudroom/porch. There'll be 2 good doubles and a study/small 3rd bedroom. I think that'll be enough for me. Good info re the insulation, thanks. Yes, I'm planning on having most of it vaulted.

My view on any significant solar gain, is that it's going to be happening in the warmer months, when the external temp is elevated also. This is where the electrically operated opener comes into its own, as the warmer air is going to travel up into the ceiling void where the rooflight is positioned. If that is opened up, it allows that warmer air to escape. If it were a fixed rooflight, then the need for control of any gain is more crucial yes?

I'm not a 1.5 storey fan although I have lived in a few. Single storey form factor is pretty pants especially if every ceiling is vaulted, like our house. You can compensate but insulation value needs to be sub 0.1 everywhere. We settled for 0.09 floor and 1.1 roof and 0.14 walls and triple grazed. But would add more insulation doing it again. Single storey is great to live in, when my wife broke her ankle, life was pretty normal - toilet, showers, beds all just as normal, no special arrangements. We did 193m² and it's 3 bed all bedrooms are generous doubles, lounge is good and roomy etc. It all could have been smaller.

If you want all the cooling now, go for two temperatures, if you want slow and steady cooling just do one temperature. Really depends on the depth of your pockets now and for running costs. Cold temperatures are just like high heating flow temperatures they take a big chunk out of your expected CoP.