Garald

Update: ISOVEO just answered: - yes, they can line all the skylights with 2cm cork within the plasterboard... and charge me 1300 eur more for it (OK, there's lots of skylights, but still); - to my question of whether we wouldn't need an airtight membrane outside the insulation in addition to the vapor-proof membrane below the insulation, they answer: "L’air doit circuler sous la toiture, mais pas dans l’isolant bien sur. Il ne circule pas dans l’isolant car nous prenons soin de ne pas laisser de passage d’air là où nous posons l’isolant. Nous veillons à bien calfeutrer partout avec l’isolant. Enfin, votre toiture protège de la pluie et à moins de déposer la toiture, il n’est pas possible d’installer un pare pluie qui se situe au-dessus des liteaux." TF;DR: no such thing is needed, in part because it's not really possible (without undoing the roof, which would cost a fortune) and in part because they take care of "calfeutrer" (literally: caulking; meaning filling a space so that it is impermeable) everything with the insulating material. (In fact, they had told me verbally before that that's why they prefer to work with wood fibre rathern than cork.) Does that make any sense? I'll try to coax a more reasonable quote from elsewhere.

Aha - how do you do that? (Can it be a DIY job?) At any rate, as I said, the plan is shelved now in my case - not enough land.

I get the feeling that here they are standard enough that the basic measures to be taken are agreed upon. https://conseils.xpair.com/consulter_savoir_faire/puits-canadien-ventilation-double-flux/description_puits_canadien.htm#part-1237 Reading a bit more - it seems this is not a possibility for me; the coop simply doesn't have enough land (you need to fit straight 25m-long tubes somewhere; some say 50m are better).

I'll try to talk in the next few years to people here who have one installed. (It's a fairly common thing in France among reasonably eco-conscious people.) In my case, it's something to consider doing 5-10 years in the future (or the next time we need to rip up the courtyard, whichever is sooner). I take it's out there in the fruity fringe in the UK?

That’s what I went for!

Understood. (The insulation company just sent me an Ubakus model - I can do that myself in a second, and so can anybody else. WUFI sounds a bit trickier - don't know whether they handle that themselves.) What about, um, keeping any water that gets past the tiles from dripping its way past the insulation? Does the airtightness membrane also take care of that?

Come to think of it: what would be wrong with just having expanded cork *exposed*, without a plaster finish, at least in sections of the ceiling? On top of that, one would still need an airtight membrane (and a watertight membrane? - or can one membrane fulfil both roles? I think the crucial thing would really be to keep water from filtering down...). By "sections of the ceiling" I really have in mind the lower part of the ceiling in half the attic - the part that is my home office. If I did that to the bathroom or my girlfriend's home office, she would murder me with an axe (or whatever vegans use to murder). (Would dust get in expanded cork's interstices? I have allergies.)

Well, around the windows, I can put as much cork as I want. The minimal spacing between windows is 10cm. Right now the insulation between pairs of windows close together is as thick as elsewhere (which is idiotic and not what was planned: it makes one hit one's head); I think 5cm should suffice, no? If an insulation company tries to overcharge me for it, I can tell them I can buy the cork and paste it myself. There's no magic to it, no? All one needs is cork (expanded or not - would it matter?), glue and a cutter.

Come to think of it, those spots you mention might be even more critical when it comes to sound insulation (since sound, again, finds the weakest point - and the skylights themselves are double-glazed; one might hope, but I can't know, that the frame is made so that it is not the weakest point itself). In that case, the thing to do might be just to put a few cm of cork around them, behind the plasterboard. Probably a wiser choice than putting PIR, say, which would insulate more but do nothing for noise.

On liege24: who on earth charges so much for two *samples*? https://www.liege24.fr/shop/42-echantillons-de-liege/1161-eacutecorce-de-liege-decoratif-mural-virgin-amp-cameleon---ensemble-dechantillons---2-pcs/ Elsewhere, prices are more reasonable - see, e.g., https://www.toutleliege.com/22-les-decos-double-epaisseur-6-mm-et-plus Or yet again https://magasindeliege.fr/liege-mural-echantillons-virgin-river.html Wonder how to compare the quality in an objective way.

Right, I've thought about that. Is there any solution to that? (In a future society, maybe windows would be surrounded by a layer of vacuum insulation, but I doubt a random insulation person who is trying to charge me twice what he should would agree to it.)

Oh, I solved my first-floor noise problem (expensively!) by having a new set of sliding windows (heavy single glazing, high transparency) installed 15cm away from existing double-glazed windows (which had good specs, but were not top-of-the-line; the fake architect got in the way of that, unfortunately). So: outer set sliding sideways, inner set opening inwards. But that's not what I meant! These are skylights, which open by tilting. Aha? What do you mean? I can share pictures (and a plan) if that helps.

Ah sorry, meant 15cm! Test for what - for the look?

I suppose the alternative is to get new, triple-glazed Velux for the three southern-facing skylights, and move those three double-glazed Velux to create new skylights on the southern side, thereby giving me a nice view from my desk... but I'm starting to think that most people here are not friends of having lots of skylights.

In fact, why shouldn't one be able to paste an extra layer of heavy, high-transparency plexiglass 6cm away from the skylight's glass? There's an indentation that makes this very tempting. I suppose that the inside could get very hot. I guess that indentation is there to accomodate Velux's own blinds, but I don't see anything noise-reducing in their product line.