nofam: (cut) I'm only talking about a kitchen/living room/foyer, so it's probably only 70 m2, and I'm not worried about it being toasty enough in winter to walk around in bare feet. I totally get hydronic heating for whole house, as it's eminently sensible, but I struggle with the cost for the benefit of 1/3 of the house. As mentioned, my primary interest in concrete is for the aesthetic aspect, followed by easy cleaning etc.
I may be a stuck record on this but I'd like to reiterate that I (and clearly many others on this forum) think you're taking a significant risk in not putting in underfloor heating, at least in the area where you'll have exposed concrete floors.
Have you experienced what such a floor feels like in the depths of a Dunedin winter? I wouldn't rely on anything I've read or been told about how insulating/isolating a slab makes it ok warmth-wise, as once you've NOT done it there's no retrofitting possible!
As others have also pointed out, if you don't at least provide the pipework for such heating there is a significant risk you'll impact on the potential resale value of the house, when/if you come to sell. I know many people (including myself) that wouldn't contemplate buying a house like that, even in a warmer climate let alone Dunedin.
Surely in the grand scheme of the significant costs of building a house you can cut some corners elsewhere to at least future-proof the house in this way?
Personally, I can't wait for the trend of polished concrete floors to end (aesthetically cold and sterile), but if you're gonna do it do it properly I reckon!