Energy-Efficient Windows near you

Most Australian glazing decisions come down to which direction the heat is travelling for most of the year. In the tropical north the whole problem is solar heat coming in, so the priority is rejecting radiation: shading first, then glazing that admits less solar energy, with insulation against conducted heat a secondary concern.

In the cool temperate south and the highlands the problem reverses for much of the year. Heat leaving through the glass on a winter night is the dominant loss, and the priority becomes reducing conduction, which is what double glazing and thermally improved frames do. Winter sun entering a north-facing window is then useful rather than unwanted, which is why blanket solar rejection can make a southern house worse.

Part H6's structure reflects this directly: cooling load alone in climate zone 1, heating load alone in climate zone 8, and both in the zones between. A supplier who recommends the same specification for every elevation and every state is not designing, and the reference-building comparison is unforgiving of that.

Part H6 of NCC 2022 Volume Two sets the energy efficiency requirements for Class 1 buildings. Its performance comparison is expressed against a reference building: in climate zone 1 the cooling load must not exceed the reference building's, in climate zone 8 the heating load must not, and in climate zones 2 to 7 neither may. Alongside that sits the whole-of-home requirement that the energy value of the building's domestic services must not exceed 70 per cent of the energy value of the stated baseline.

Part H6 does not itself carry numeric glazing performance values. External glazing and shading are dealt with through the ABCB Housing Provisions, which is where the envelope requirements live. Glazing as a product is handled separately again, in Section 8 of the Housing Provisions, which is divided into scope, windows and external glazed doors, glass, and glazing human impact.

State variation matters here as much as anywhere in the Code. New South Wales deletes one of Part H6's verification methods, and Tasmania and the Northern Territory carry their own Part H6 provisions. Part H6 of NCC 2022 applied from 1 October 2023 after a transitional period that began on 1 May 2023.

Replacing windows is rarely the cheapest first move in an existing Australian house. External shading on the elevations that take the summer sun, insulation in the roof, and sealing the obvious air paths usually deliver more comfort per dollar spent than new glazing does, and they do not require the wall to be opened.

Replacement earns its place when the existing windows are failing anyway, when a room is being renovated and the wall is open, or when the specific problem is conducted heat loss on winter nights in a cool zone, which shading cannot address. Secondary glazing, a second pane fitted inside the existing window, is a middle path worth considering in heritage-controlled houses where the original windows cannot be changed.

The honest test is to ask what the windows are being blamed for. A west-facing room that overheats in February has a solar problem, and glass alone is a partial answer. A southern living room that is cold at nine at night in July has a conduction problem, and that is what better glazing is for.