Keep in mind that the insulation benefits are not what they seem.
Everyone focusses on R rating, which is about 1/3 of the picture. This is because the ratings programs model a house as a simple box and ignore reality.
Case in point - cavities are important. In a double brick wall, when the outer course gets hot in the sun, it creates a chimney effect within the cavity that draws in cool air from the rest of the house cavities (which don't have sun on them). This cools down the bricks in the sun and significantly reduces heat transfer to the inner course. Add a radiant and conductive heat barrier (foam with double sided foil) in the cavity and maintain the air gap on both sides and you have a wall that beats massive R-ratings in the real world. R-ratings don't consider any of that effect but put a temperature probe in the wall, or take the tiles off a cavity that is in the sun on a hot day and stick your head over it and you will see the difference is huge.
Likewise, most of the heat transfer from the roof to the house occurs where it is closest to the house (behind the cornices), yet all the insulation goes in the ceiling, ignoring the transition from the cavity to the ceiling, which is where most of the heat flow is.
And again, everyone focuses on the same thing with windows with double glazing, which perform just as badly as single glazing in most cases without a radiant heat barrier (e.g. comfort glass), particularly on west or east walls.
You can have a single glazed double brick house with hardly any insulation that doesn't really need heating or cooling and out performs a 9 star house with these fancy materials if:
- You have lots of north facing windows to heat the slab in winter - no garages on the north side! After a good day in the winter sun that slab will take five days to cool down even without insulation.
- You have no east and west facing windows
- You plant some deciduous greenery around the house or have a vergola to reduce the heat that reflects back into the house from hard surfaces in summer.
This was all demonstrated decades ago by people like Griff Morris in Subiaco but nobody wants to know about it - likely because there is no money to be made out of the basics. Instead most people end up with the icing instead of the cake....
All this R-rating focus and double glazing etc does my head in - it's designed for very cold climates where it makes a real difference. Perth has a mediterranean climate and that has different rules. Yet these modelling programs and star ratings pretty much assume assume we all live in Norway! Or just want air con regardless of whether we need it.