WERS Window Ratings Explained

When a committee collects quotes for new windows, every supplier says their product is energy efficient. The Window Energy Rating Scheme (WERS) is how you check. It is run by the Australian Glass and Window Association and gives each window and glass combination independent, comparable figures. This guide explains what those figures mean and which ones matter for a strata building.

What WERS rates

A WERS rating is for the whole window: frame and glass together, as one product. The same glass in a different frame gets a different rating, and so does the same frame with different glass. That is why one window style can have dozens of ratings, one for each glass option the manufacturer has rated. Each has an ID you can look up in the WERS database.

Uw: how much heat gets through

Uw is the whole-window U-value, measured in W/m²K. It tells you how much heat passes through the window for each degree of difference between inside and outside. Lower is better. Old single glazed aluminium windows rate around 6 to 7. Good double glazed windows rate in the 2s, and the best rate below 2.

Uw matters most in winter and in buildings that run heating, and it is also a fair guide to comfort near the window in any season.

SHGC: how much sun heat gets in

The solar heat gain coefficient is the share of the sun's heat that ends up inside, on a scale from 0 to 1. Lower numbers keep units cooler. In Sydney this is often more important than Uw: a west-facing unit with a high SHGC overheats every summer afternoon, however good its U-value.

Low SHGC is not always the goal. A south-facing unit that never gets direct sun can benefit from a higher SHGC in winter. A good proposal sets SHGC by orientation rather than using one glass for the whole building.

Tvw: how much light gets in

Visible transmittance is the share of daylight that comes through, again from 0 to 1. Some low-SHGC glass also cuts a lot of light and makes rooms darker. Check that the glass chosen for heat control still lets enough light into living areas.

Air infiltration

Air infiltration measures how much air leaks through the closed window, in litres per second per square metre. Lower is better. Hinged windows that close against a seal (casement, awning, tilt and turn) usually leak far less than sliders. Leaks bring in draughts and noise as well as heat.

Star ratings

WERS also gives each window a heating star rating and a cooling star rating out of 10, calculated for a typical house. They are a quick way to compare, but the stars hide the detail. For a strata building, look at Uw and SHGC for the windows on each elevation.

How to compare quotes

• Ask every supplier for the WERS ID of each window and glass combination they are quoting
• Compare Uw and SHGC for the same window type, not the best figure from each catalogue
• Check the glass is matched to orientation: lower SHGC on west and north elevations, more light where rooms are dark
• Compare air infiltration if draughts or noise are a complaint
• Remember WERS does not cover wind and water ratings, which come from separate AS 2047 testing

Our ratings

Our thermally broken aluminium windows are Alspec systems, fabricated by AJ Aluminium, and listed in WERS. Double glazed, they rate from Uw 2.4 for awning and casement windows and from 2.0 for sliding doors. The full table is on our thermally broken aluminium page. Our uPVC frames have frame U-values as low as 0.77 W/m²K. Every proposal lists the rating for each window type quoted.