craig

Correct, that's the same for the external canopy.

Those fixings would be ideal in this scenario for you.

Have you considered just using glazing beads and hidden fixings though the bead and finish with glazing tape and silicone bead around the glass? The beads are generally what hold the glass in please.

Either agrees or took the lesser of two evils, I'll go with he just didn't want to fight it further. Either with legal advise or not. I'd suggest he has been informed that he'd lose and incur the legal costs as well to defend it further and would end up costing him a lot more, an excellent result for you. Unfortunate it has had to go the way it has.

I would say that is the intended design.

No, no slope required as that is the area where the glass packers need to be. It is externally glazed though, which means the cladding needs to be removed to get access to the glass if it breaks/fails. This is the case for most outward opening systems, the clips break when removed, so they need to be replaced and service engineers absolutely hate them, as it's it a lot of time (money)/effort to remove all the cladding, place the clips back, and fix the cladding back on. That also means they need to have the right tool to turn the clips to hold the cladding in place (they get broken removing the cladding, easier to snap the lug than turn the clip).

CT1.

They're a practical window, easy to slide up and down but they are far from being "decent" - just the nature of sash and case.

It’s not really my area of expertise tbh but @Nickfromwales might be able answer these questions better than I can?

Fold it over the top of the PIR and seal it to the DPM/radon barrier I think would be the best approach.

Sticky tape? They should have used something like CT1 or stickslike***t would have been good enough and then trim if required. Should be fine, not much else you can do from what I can see. Any left over to patch? If yes, stick over the top with the adhesive mentioned previously.

It was more tongue in cheek than anything else.

Exactly this, with MVHR there isn't really any need to have it open and actually better if it isn't because of losses in heat recovery "if" it's open to deal with steam etc. It's not just about heat recovery but also to disperse smell, someone drops one and you can't open the window, the poor bugger that goes in afterwards is going to a create a clean up in aisle one to deal with.

They can do both open and closed.

It shouldn't ever require the customer to come up with a detail for thermal detailing but in all honesty, it's not really something the installers know about either in the typical replacement window market which is not the market that most people on here are looking at. They "know" about removal and installing back in the same place with new windows. If they also surveyed, they should be allowing appropriate tolerances (usually 5mm all around on a replacement and dependent on opening, it may require 10mm or more). It would be interesting to see the report from Fensa and what wasn't in line with building regulations and why if possible?