In defence of the builder, none were perfect, but this one was much worse than all the others.
My mate is really, really happy with the work that's being done. I just bite my lip when he shows me around, same as I've taken to doing with just about every other recent extension I've been shown around by various friends over the last couple of years. This is also a rare case of me raising insulation for discussion. I've learned that people don't know and quite literally don't care, and indeed, get defensive if you try and discuss improving insulation and airtightness. The attitude seems to be that it's fine if you want to build an "eco-house" like we did, but that all that stuff isn't relevant for an ordinary build.
All anyone seems to care about is how big the kitchen is and how wide a set of bifolds they can get away with.