It's been a week since we put insulation into the roof and the effect has been instant! Temperatures through the whole house are consistent throughout and it seems to be holding more warmth, and for longer (based off the HRV console, which tells us the temperature in the roof and in the house).
I went with these ceiling insulation pads - local, nontoxic, precut to fit standard timber framing for easy DIY. We wound up with 3 bales left over; a product of having to guess at the size of the house/roof, and the way that the sunroom (dining nook) was added onto the original house meant that extension didn't really lend itself to adding insulation over that part.
So, if anyone in Auckland is after some Greenstuf ceiling insulation pads, leave me a comment below and I'll email you! (Your email won't be visible to anyone except me.)
There are 3 bales, R 2.9, each cover 6.82 sq m. all untouched and unopened. They retail in the range of $107-$130 depending on where you go; happy to knock off a few bucks.