Energy report...need darker roof?

Hi all,
We're currently in the back and forth between the builder and draftsman and the energy report has come back with a 6.2 star rating. The minimum required is 6.
The confusing thing for me is that they require a dark colorbond roof to achieve this rating and we'd prefer a light coloured roof. First off I would've thought the light colour would help with energy efficiency. Now I'm sure there's other ways we can bump the rating up which were waiting to hear back about, however I don't get how we didn't easily achieve the rating in the first place.
We've spec'd double glazing throughout, anticon roof blanket, r2.5 walls, and r6 ceilings. How do volume builders which don't even supply double glazing as standard get anywhere close to meeting the 6 star energy rating?

Is there something I'm missing here?

as i understand the rating system, there are several measures that are considdered and sometimes how they are met raise an eyebrow.

That said, i know when we were going through the process of achieving the energy rating, we could get some things done in lieu of others, that achieved the rating. ie after learning our houses wouldnt be connected to recycled water, we had to either chose solar gas boosted hot water (over instantaneous) or put in a rain water tank. One option credited me 2.5k, the other one would cost me 4k.

SO work with your builder on what's available to you and you should still be able to get your light colored roof IMO

Its all depends on your location specific climate, orienation due to north, windows (size, placement, location), double storey or single, open floor plans generally have lower rating compared when rooms are closed off, quantiTy and location ot thermal mass (usually slab) exposed to winter sun. Bigger houses achieves lesser stars than smaller house. There are so many variables. Share your floor plan and people here will understand more as well as your climate zone.

There are many types of glass, is it air between the two glass or something else, your window frames is it a standard one or a thermmally broken aluminum or pvc or timber.

This is is single glazed in low e and achieves 10 star.
Lots of thermal mass. Also note a 10 star in Brisbane when built in Canberra willl have a lower energy rating due to climate location



https://joshshouse.com.au/

Thanks for the replies so far!
So I spoke to the draftsman and as stated above, there's a million things that get taken into account when determining the energy rating.
In our case, the biggest thing that dragged us down was the slab. We're using a raft slab and due to the large uninsulated surface we lose out compared to using a waffle pod slab. They're going to give us a quote on an insulated slab.

The next biggest thing is the windows. We have a lot of windows in the house and although they are double glazed aluminum with argon fill between the glass, they are not thermally broken from the frame.
They suggested we could get thermally broken aluminum or better yet pvc frame.

We're going to get all different options quoted and see what's worth while. We really want a highly efficient home but it all comes down to cost as to how far we take it unfortunately.

Have you considered structural insulated pAnels?

We have. And the quotes we got were out of our budget for the home we wanted. Also added to the cost of electrical and plumbing fit out.
I'd love to go down that path one day (possibly go full passive), but at this stage it's just not common enough to be cost effective.

Which state are you in? A warm climate should have a lighter colored roof - if you're in a cold climate then maybe a darker roof might be more energy efficient but I don't honestly know.

The bulk of energy efficiency gains will come from design and orientation; reducing total area of glazing etc. Apart from what you've already mentioned, window frames are very important (including the colour) and also sealing on doors and windows. The actual installation quality of the insulation will be very important in what you actually experience - dodgier builders won't go to the effort of making sure that the insulation fills the corners etc.

With regards to your second last question, I believe there's all kinds of loopholes available to achieve the energy efficiency rating.

They've already called out that the raft slab has played a significant role in reducing the energy efficiency rating.