NCC 7-star rules and your windows

What does 7 stars actually measure?

It is a thermal rating, scored out of 10 stars↗, for the heating and cooling energy a home needs to stay comfortable. It says nothing about your appliances. That is the second number: the Whole of Home rating, scored out of 100↗, which covers heating, cooling, hot water, lighting, cooking and pool pumps, less anything solar puts back. In Victoria the Whole of Home figure has to be at least 60↗.

Where do windows come into it?

Glazing is the weakest part of most walls, which is why it carries its own provisions. YourHome puts the loss at up to 40%↗ of a home's heating energy, and the gain at up to 87%↗. A designer trades window size, orientation and performance against each other to land the rating, and the ABCB publishes an ABCB glazing calculator↗ for working the deemed-to-satisfy version through.

Is it true that the tropical north has no glazing rules?

No, and this one travels a long way. Zone 1 is treated differently, with a different formula in zone 1↗ because there is little or no heating need, so it sits outside the conductance table that covers climate zones 2 to 8↗. The solar heat gain limit still applies there: it runs across climate zones 1 to 7↗. If anything, zone 1 is where keeping the sun out of the glass matters most. Zone 8 is the one left out of the solar heat gain check.

Do the 7-star rules apply when you replace windows?

The star minimum is written for new homes, so a straight window swap in an existing house is not rated against it. That is not the whole story in Victoria. The building regulator says full replacement of building elements is treated as an alteration↗, and its guidance is that extending or substantially renovating a home, more than 50 per cent↗ of it, may bring the current energy requirements into play. A registered building surveyor is the person who decides where your job sits.

How do you find your climate zone?

The ABCB publishes a climate zone map you can search by address or postcode. Melbourne, for example, is in climate zone 6↗, where summer cooling and winter heating both count, so a window choice that is right for Brisbane can be wrong there.

This is a summary of published provisions, not a compliance check. For a building permit, the numbers come from a NatHERS assessor and a registered building surveyor.