The building industry in Australia represented by HIA and Master Builders are addicted to low-cost windows. From the 1950’s onwards, glazing became cheaper and allowed architects to frame views and bring light into the building.

Also, builders realised that windows at that time per square meter were only about half the cost of a wall. So, with using more glass, one could construct cheaper buildings. As a solution to keeping such glasshouses at a liveable temperature, larger air-conditioning systems were required.

Central Europe:

Houses and windows in Europe developed quite differently. In the alpine region already a couple of centuries ago they installed casement windows with sashes fitted to the inside of the wall and again also windows on the outside. The climate was harsh and energy scarce.

The early 70’s brought the energy crisis and Governments desperately tried to reduce energy dependency through regulating the market. Badly built homes were seen as energy wasters and regulations and incentives were introduced.

Passive house was then the next step which really changed the market. Today few people would consider building a house which has not at least had a blower door test done to measure air infiltration, whether it is a standard home, low energy home, zero-energy home, or a Passive House.

Poles Apart

In Australia, the building industry now finds itself in these interesting times were we still have on the one hand 80% single glazing and on the other hand a market that is pushing the boundaries with Passive House. The recently updated NCC (National Construction Code) will improve the bottom end of the market somewhat – especially in Victoria and New South Wales - with requirements that call for minimum energy efficiency for a new home’s building shell of 7 stars out of 10 through the Nationwide House Energy Rating Scheme (NatHERS). The rating measures the energy needed to heat and cool a home, adjusting for different climate zones.

Windows play an essential role in the structural and environmental performance of buildings. Poorly manufactured or standard windows lose more heat in winter and gain more heat in summer than any other surface in a building.

Window Performance

The thermal performance of a window can be measured by its thermal transmittance or U-value, which measures heat transfer through the window via conduction. Lower numbers indicate superior thermal performance. Solar heat gain coefficient (SHGC) measures solar radiation passing through the window. Lower numbers here indicate more shading. Glazing elements must be rated as an entire system to account for the different thermal properties of glass, any fills, the frame and the impact of the frame on the glass. Window performance can be checked on the WERS (Window Energy Rating Scheme) website.

Investment

Building a house with large glazed areas to a higher energy standard will be a bigger investment at the start but with large savings on energy bills for the life of the building. Then again it is not just energy savings that should be taken into account when deciding to use high-performance windows but the comfort they provide with a more even indoor temperature that encourages the pleasant and satisfying feeling of physical and mental well-being.

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