How to Read Window Energy Ratings: U-Value, SHGC and WERS Explained
Windows make or break a NatHERS rating. Here is how to read U-value, SHGC and WERS labels so you choose glazing that passes 7 stars without overspending.
Windows are one of the biggest influences on a NatHERS rating. They let in winter sun and summer heat, and they lose warmth far faster than an insulated wall. Choosing the right glass is often the difference between passing and failing 7 stars. The trouble is the labels: U-value, SHGC and WERS. Here is how to read them.
U-value: how well the window insulates
The U-value measures how easily heat passes through the whole window. Lower is better. A low U-value keeps warmth inside in winter and out in summer. Single glazing has a high U-value, while double glazing and better frames bring it down.
SHGC: how much sun heat it lets in
The Solar Heat Gain Coefficient (SHGC) measures how much of the sun’s heat passes through the glass, on a scale from 0 to 1. A high SHGC is useful on north-facing windows that you want to catch winter sun. A low SHGC suits west-facing windows that you want to protect from harsh afternoon summer heat. The right choice depends on orientation.
WERS: the independent rating
The Window Energy Rating Scheme (WERS) rates windows for both heating and cooling performance using star ratings, so you can compare products fairly. WERS-rated windows give your assessor reliable figures to model.
Matching glass to orientation
| Orientation | What to aim for |
|---|---|
| North | Moderate to high SHGC to capture winter sun, with good eaves or shading for summer. |
| West and east | Lower SHGC to block harsh morning and afternoon heat. |
| South | Low U-value matters most, as these windows get little direct sun. |
Frames matter too
The frame is part of the window’s performance. Aluminium conducts heat readily unless it is thermally broken, while timber, uPVC and composite frames insulate better.
Frequently asked questions
Do I always need double glazing? Not always, but it is often the easiest way to lower U-values and reach 7 stars, especially on exposed elevations.
Is one window spec right for the whole house? Rarely. The best result usually mixes specifications by orientation.
Not sure which windows your design needs? Get a fast, fixed-fee quote and we will model the glazing that passes 7 stars.
Free guide
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BASIX & NatHERS specialists helping NSW homeowners and builders achieve energy-efficient, compliant homes.