Mike

FWIW, I avoid using glassfibre now; it's not much fun to work with, even with a respirator & gloves.

I've used the 3M 6200 half mask for years - not sure if this is my 2nd or 3rd (the others wore out) - similar to the Dewalt one. I used a couple of other brands in the past, but ended up throwing them because their proprietary filters became unavailable. That's not been a problem with 3M. For dust, I use the 2135 filters; a pack of 10 pairs will last me for months or longer, depending on the dust levels.

From experience hemp is good to work with but really tough to cut - a toothed blade is impossible. If you're doing a small quantity, then you can get away with the Bacho Profcut PC-22-INS insulation saw, though it works works better with normal insulation (EPS, XPS, etc). For larger quantities of hemp or woodfibre, it's essential to invest in an electric saw with wavy-edged blades, which make it almost as easy as cutting butter. I only know of 2, but there must be others: Bosch Professional GFZ 16-35 AC + the TF350WM blades (I got through 2 pairs) - demo if you look for the video at https://www.bosch-professional.com/fr/fr/lame-de-scie-tandem-pro-fibre-insulation-tf350wm-3053403-ocs-ac/. Festool 577231 18V cordless You may pick one up on eBay, as I did.

You live in France. I don't remember them being that bad last time I visited the UK. Though it's been a long time since I made it to Cornwall...

Overall, remarkably accurate. Starting with all that 'clutter' in the fist section - all now available on your smartphone. They're partly right - you can recharge that smartphone wirelessly. Thankfully! And fashions have improved too.

At that thickness even the most expensive insulant won't do much; in fact it would be more-or-less decorative as it would be bypassed by the outer skin sitting on top of the beam (and maybe by the patio door). You may be able to build the brickwork off Armatherm (ask them), but if the brick is already in place there's no good solution. Other than to dismantle it it and approach it differently (and claim the cost back from the structural engineer who designed it?)

I've done similar, though using a plastic angle to keep them straight.

This will give you a clue: https://www.researchgate.net/figure/sopleths-for-growth-of-various-fungus-species-and-the-lowest-isopleth-for-mould-LIM-0_fig1_272886603

+1 for blown EPS. The silver / grey ones provide somewhat better insulation than the plain white.

If under a warm / hot shower I doubt MVHR on boost would give you any discomfort in an open room. There's scope for some consumer testing here - just don't post the photos :)

Zehnder's recommendation is that it should be close to, but not directly over, the shower. No reason given, but my guess is that it's not about the functioning of the MVHR unit, but rather that the air being drawn past the person showering could, in some circumstances, feel uncomfortably cool. For example if you don't have a good shower screen & door in place.

You'll still want to keep a healthy indoor air quality, so you'll need it running to ensure that the air stays fresh. And if there is condensation within the unit, the fresh air running through it is more likely to help to keep it free from mould compared to stagnant moist air in the unit if you switch it off. So I'd keep it running.

I'd like to fit 230V Tridonic LED light engines, pictured below, (as suggested some time ago by @Carrerahill https://forum.buildhub.org.uk/topic/13775-led-llmf/#comment-227778) in some plaster-in downlighters. The instructions for the downlighters show two different mounting options for the electrical connection. 1) Shove the connection block / transformer at least 20mm away from the lamp, which would work: 2) Mount the connection block on a stirrup (supplied), which doesn't work when using a light engine... ...if you've not already spotted the problem, the stirrup is fixed to the part of the downlight that's plastered into the ceiling. But a light engine needs wiring to the connection block; do that and you can't change it if it fails, unless you rip the fitting out of the ceiling. So option 1 seems the logical thing to do. However must be some regulations that require the use of the stirrup in some circumstances - otherwise, why supply them - but If there are, I can't find them, and the supplier can't tell me either. I only recall stirrups being used with GU10 (& maybe Gu5.3) lamps, so my guess is that it's a requirement for them. But as one of those could be retrofitted to replace my planned light engine, maybe that still needs to be taken into account. But then why show 2 mounting methods? Going round in circles... If anyone is able to, err, illuminate me with what regs apply and when, that would be very helpful.

If inadequate insulation is indeed the problem, then it's either a specification or installation issue (unless the design required someone else to do something - for example to bury the ducts in the loft insulation).

If there's a long run of poorly insulated duct through a cold attic, then that would certainly be the expected result.