Redbeard

Well, it involves bits of bent metal, so it's 'after my own heart'. I'll have a closer look later.

Many would say so. I say not, as the VCL is there on each sheet, but not at the joint. You go on to say 'Traditionally', nothing, which is why I prefer working with insulation only (say foil-faced PIR), taping the foil face , then battening and hten boarding. However a few people have started to use 'fluff tapes' like Contega or Pavafix Win, over which you can plaster, so that would work, although strictly that 'bit' of the VCL is not in quite the 'right' place. I think you can get a 'tighter' VCL if you use bare boards and separate plasterbds. I rarely use foil tape - it's too variable. I prefer to use Pro Clima or similar air-tightness tapes.

What renderboard had you planned previously? Does it have to change? Do you want to get more insulation? You could use wood-fibre board (lambda somewhere 0.039-0.044W/mK). I used Baumit Silikon Top. It comes in varying grit-sizes, from really gritty to almost smooth.

OK, try again! I cannot see how wide your butt joints are, but could you have it galvanised with one end flat and the other rising and curling over the curved section of the next tile. But how does one stop water running down the strap? And again...! Brackets shaped to sit over the ridge with 'wings' rising up the triangular edges of the ridge tile to 'hug' them - maybe 2 per tile, and somehow with some 'spring' to the 'wings'.

Oh bu--er! I have just looked at your pic again. I was thinking of bog-standard Victorian terrace ones like mine, where each one has a 'hood' which overlaps the next. That won't work with your plain-ended tiles. Will see what else I can think of.

I think in a straight fight between your mortared wall and a combine I know which I'd bet on 😉but it may help against the sheep. Sad, though., It looks the business.

Hmmm... a) I share your pain! b) Maybe there is (though I am not certain for refurb) due to the feeling that mortar and gravity are not going to hold your ridges forever. I wonder if you could satisfy them if you did some clever metal strap-wrangling so that you could trap down each 'plain' end below the 'oversail' of the next. If you used, say 3mm steel and worked it hot (or got a fabricator to do so - all they need is your sketch and dimensions) this could work. But it would have to 'work' for roofer and BCO. If I had such lovely ridges I would be happy to finish that myself if BCO would accept it.

The lack of a completion cert suggests it has not been signed off! (Surely). I always received completion certs for my jobs. The heading says 'Date of Completion Cert (If issued)' and the comment is N/A. I would read that as 'It is not applicable because there is no date, because there is no completion cert', but I see that in this case they use it as 'not available'. Either way I don't think that helps you, as it could be 'not available' 'cause they lost it, or because there never was one. Of course I could be wrong....

If you go with Wood-fibre you could go to a merchant which offers (dynamic, more accurate, condensation risk assessment) WUFI for free. Building Control depts are very variable. Mine used to be quite hard to get a conversation with, so if you were doing anything with any element of doubt you just had to go with your gut and hope the BCO agreed. Since they may only do 2 (or even one) visit(s) you don't, ideally, want to wait till you have done something (based on your best researches) to get a BCO opinion on whether you've done right. They should have no problem with an area-weighted calc, and should also be OK with you not quite achieving 0.3W/m2K (0.3 with WF may be an IC risk). I used to use the WUFI calc to back me up on that. On the other hand some merchants do a cost/benefit trade-off and suggest even less than I'd use. Not sure always how you get that past BCO. My feeling re WF is that if it functions without a VCL then you don't have a VCL to get wrong. Just go tight as a tight thing and stuff any gaps with 'fluff' (cutting 'swarf' mixed with water). Always use a (lime, in my view) parge coat. Views about gypsum as an under-layer vary. As I say, I have used PIR when the client cannot pay for WF, but I'd much rather use WF.

But surely the hole will be in the right place

I am sorry you have had a rough time. I picked up on the words 'acting as my electrician'. Are they one? If it were me I guess I'd be looking at the terms of the original agreement (which might be the 'feel' of it if it was verbal). Did any particular thing precipitate the decline of the relationship? Have they done of not done anything which might be of interest to Trading Standards? Oww! 'Multiple more thousands' sounds painful. I don't know much about the Small Claims Court but is there a clear breach of what you thought they intended to provide?

If I were doing something like that I would use Pro Clima's Intello (which is vapour-closed in low temperatures but becomes slightly vapour-open as te weather warms up, allowing 'dumping' of any accumulated moisture) as VCL, not the foil on PIR, so just make the wall as thick as you need to get the U value you want without the PIR, then it could 'breathe' (a bit) both ways instead of being 'blocked off' on the inside.

Sorry, that's drivel!! Reaching the dew-point on the inside of the external wall is more likely with thicker insulation, not thinner. I know that! I think my brain must have gone on holiday for a few minutes... Oops! Try this: I would not recommend having no insulation at all in the shutter-boxes. If you can use a high-grade insulant (such as the aerogel you referred to) to ensure that the surface is warmed up sufficiently in the shutter-boxes for condensation not to occur then (though the insulation value may still be cr*p compared to the rest of the newly-insulated wall, you may avoid a local mould problem inside the shutter-boxes.

Welcome! Showing that an impermeable insulant works is generally done with the aid of a 'Glaser Method' condensation risk assessment (henceforth CRA so I don't have to type that again). Glaser method is the British Standard method, still, AFAIK. It is not a 'dynamic' tool and is a bit of a blunt instrument. Again, AFAIK, it always did assume, and I think still assumes that all moisture in a wall comes from inside (in the form of water vapour). Therefore a sheet of foil will stop all moisture and everything will be hunky dory. Each of your composite boards has a VCL. Where is the VCL at the joint? I have favoured wood-fibre (and a request for a waiver on the U value) for a long time, but if I was doing PIR for clients I would use 'raw' PIR at 50mm, taped at all joints and perimeters, battens to fix it to the wall and a further 25mm PIR before plasterboard. You have to be really picky to get the VCL right. I prefer WF which has no VCL. No VCL = no VCL to get wrong. Just a pedantic point -sorry! - you say 'high U value'. High insulation value, which is a low U value. Also, to get 0.3W/m2K on a solid brick wall you will need a board of about 70mm (60 insulation and 10ish plasterboard) so your shutters won't work anyway. What thickness is your builder proposing? Who is doing the Building Control application. (In case it has not been mentioned, you need one.) You could claculate the area-weighted U value so that you could have 'fat' insulation away from your shutter boxes and thin at the boxes, but you would need to be sure that the thin insulation would not give you a dew-point. I am not sure how that would help? Do you think your bricks leak water? If they do, they'll leak with a thin thing or a thicker thing attached to them. Re the bathroom XPS will give you a VCL (the XPS is its own VCL) which you need, unless you use Wood Fibre (which is not recommended for wet rooms). But thin board won't achieve the target 0.3W/m2K U value. I hope this sounds positive, not negative! Queries welcomed.

I have done something vaguely similar, but with wood fibre. Just stagger the outside and inside verticals and make it as 'fat' as you need to get your desired U value net of the timber fraction. In my case the external members were structural and the internals not so, but it can be either way round, or indeed the load can be shared.