Mike

In Germany they brought in a law a couple of years ago that voided such restrictions: Germany Grants Renters the Right to Install Solar Systems on Balconies

The final report by ENTSO-E was published a week ago here. "the blackout resulted from a combination of many interacting factors, including oscillations, gaps in voltage and reactive power control, differences in voltage regulation practices, rapid output reductions and generator disconnections in Spain, and uneven stabilisation capabilities. These factors led to fast voltage increases and cascading generation disconnections, resulting in the blackout in continental Spain and Portugal." The summary at Euractiv says that it "paints a picture of an ill-managed transmission system, which one technical expert who did not wish to be named described as “damning” for Spain’s high-voltage grid operator." "Fully 19 of 21 recommendations to avoid a repeat of the disaster are aimed squarely at operators of high-voltage grids across Europe". However it does mention that "rooftop solar contributed to the rapid collapse of the grid. Small panels – which provide a significant share of Spain’s electricity around noon – turned themselves off in the very early stages of the blackout. Fixing this vulnerability could require potentially costly retrofitting." The report recommendation on this says this:

Leroy Merlin have the same models here in France too. Lidl are selling an even cheaper 800W version here, though it has mixed reviews: Maybe because UK RCBOs & circuit breakers are still, AFAIK, single pole (i.e. they cut only the live, not the neutral)? European circuit breakers are always double pole, which are safer than single pole under certain conditions*. So switching off the RCBO may leave all circuits with a live potential if the PV panels has been plugged into a reverse-wired socket, while the user thinks it's been isolated? *so, in Europe, there's also no need for isolating switches next to extractor fans, ovens & other fixed appliances.

2 layers is definitely a good idea. If you have a nearby installer, sprayed high-density PU foam is another option that's very common here in France. For example https://www.youtube.com/watch?v=CSZ2Mhtbq_M

If you have lots, then it could be worth getting a wavy-edge hand saw. I've got a Bahco ProfCut that works well and avoids the mess. Plus a knocked-up jig to keep the angle you want.

I too have been traumatised old Crittall windows, but their new ones are very different, with thermally enhanced / thermally broken power-coated & galvanized frames + double or triple glazing. More here. So technically they can be a sensible option, but no longer the cheap option that they once were.

They do look 1970's, but roughly like copies of Crittall windows; I wonder if that's what they replaced? Since they look similar, there may be a chance of persuading them to let you install similar new Crittall windows, on the grounds that they'd be more authentic (as well as being better insulated). If you can find old photos that substantiate my suspicion it would help.

Unless I've missed something, hempcrete still seems to be a niche product in the UK, so this newly published webinar on its use in European newbuild may be of interest. It's mainly focused on apartment buildings (with some office & commercial) rather than single homes, although there are a couple of examples of those from Australia (using a rebranded French system). Sprayed hempcrete, hempcrete blocks and prefabrication are all covered, applied to timber, steel and concrete frames. Start at 10' 50" if you want to skip the introductions.

I'm installing CAT6 too. By the time that I need anything faster fibre might be preferable (and cheaper).

I thought it worked by buoyancy, so hot are at the top, which will be lower density, will stay at the top. Yes, it does work by buoyancy - but buoyancy is driven by temperature difference. Air warms, so expands, so becomes more buoyant than the surrounding air, so will rise if it can, with cooler air taking it's place: If the internal air is warmer than the external air (e.g. in winter), the internal air is more buoyant, so will rise if it can (to be replaced by cooler outside air); If the internal and external air temperatures are identical then both are equally buoyant, so there's no air movement; If the external air is warmer than the internal air (e.g. in a heatwave), the internal air is less buoyant, so will sink if it can (to be replaced by warmer outside air). (delayed reply - been away...)

She's right. Passive stack ventilation is driven by the difference between indoor and outdoor temperatures. In winter that difference is big so it tends to over-ventilate; in theory you could devise controls to restrict that but it wouldn't be easy. On a hot summer day the indoor-outdoor difference can be small, resulting in very little stack effect, so very little ventilation. In fact the outside temperature may exceed the internal temperature, causing the stack to operate in reverse and draw in warmer air from the top down. MVHR is a more reliable choice and offers multiple other benefits as discussed in other threads.

Sure, you can choose to heat a Passihaus however you like without restriction. Perhaps because of that, many people in the UK seem to be unaware of the underlying principle behind why 15 kWh/m²/year was chosen (for European climates) - it's not a random number - and think that they need to pay for a conventional heating system in addition to all the other costs of achieving the standard, rather than offsetting the cost saving. Indeed it's so fundamental that it's the reason that the word 'passive' is in the name - it doesn't require traditional 'active' heating or cooling, because it can maintain a comfortable temperature largely through passive means. It's pretty useful to know on a thread discussing costs vs benefits. Worth mentioning too the innovative use of Willis Heaters as a low-cost heat source for those who do choose to add UFCH; there are multiple threads on the topic.

I evidently should have put this bit in bold: That is, when properly designed and built, a post-heater(s) on the MVHR system is sufficient to sustain an acceptable internal temperature. Wolfgang Feist, co-creater of the PassivHaus, has said that this is the fundamental definition of PassivHaus in many interviews over the years, including in this one from my archive (Energy Design Update, Vol. 28, No. I, January 2008): That's typically topped up on very cold days with a panel heater(s) or the like. In the UK at least, UFCH pipes are sometimes added for reassurance and / or for future summer cooing.

You may have already discounted it, but if not then you may want to consider a PassifHaus design (there are several threads on the topic). The underlying concept is that if you improve the thermal efficiency to a high level, then you no longer need a conventional heating system - and that former is paid for by the saving on the latter. That trade-off may not fully work in the UK, where the prices of certain components is higher (than in Germany & Europe more generally), but factoring in very low future heating bills (negative if you add PV) may compensate for that in your evaluation.

If you know beforehand that they won't align, then go for an architrave back box instead, screwing the light to the plasterboard either side (though the light still needs to be big enough to hide the box); I've always used them.