Building a house in the province

Thanks for the advice. Just done a bit of reading and there is another product called omniboard, do you have any experience of that?

Never used Omniboard, as to me it is still a wood based product. How well it would stand up to humidity in the long run is still an unanswered question.
We changed our exterior ceilings to spandrel a few years ago and it still looks new. Cant remember the exact cost but it wasnt expensive and easy to install.

I'll look into this spandrel because I've a feeling the carpenter will want to use plywood on the exterior ceilings which I'm not keen on at all.