Just wondering if anyone had any thoughts on this. We are planning a new self build (3000sq ft, 2 storey with hollow core slab, large south facing windows with limited northern glazing). I'm currently leaning towards external wall insulation due to removal of all cold bridges and the ability to not have to watch blocklayers constantly. However the site we have is quite hilly so the chance of driving rain is a worry. Instead of building a block on flat internally I was thinking of building a narrow, uninsulated cavity wall (50mm cavity) and then having ewi on the outside. I was thinking of this as it would give me the benefits of ewi, I would still have the "security" of a cavity from a moisture ingress PoV, it would take less blocks than block on flat and I would still have the ability to allow the hollowcore slab to sit on both leafs (with appropriate dpc).
Id appreciate if anyone could offer any opinions on this, pros/cons as all advice is greatly received.