Australian homes are often designed with large windows to allow natural light to flood the interior spaces. However, many of these windows are not energy efficient, impacting the thermal performance of the house. Utilising higher-performance uPVC windows can help address these inefficiencies – cost-effectively.
Energy efficiency is increasingly being prioritised in new construction and existing residential buildings in Australia. Cutting down the carbon footprint of our built environment and reducing carbon emissions are considered as vital contributions towards fighting climate change.
Insulation is a simple and cost-effective way to improve the energy efficiency ratings of new builds and renovations. However, by creating ‘holes’ and thermal bridges in the building fabric, windows compromise the thermal performance of the building. Glazed walls, for instance, can make it difficult to maintain a comfortable internal temperature all year round. These can be equated to an ‘open wound’ – either leaking or absorbing too much heat, depending on the season.
To understand how poor-performing windows leave a gaping ‘hole’ in an insulated wall, we have to consider how insulation and conduction of thermal energy is measured to compare the two elements – walls and windows.
Wall insulation performance is usually indicated in R-Values – a measure of how much an insulation structure will resist the flow of thermal energy over a two-dimensional surface. Windows are rated in U-values (the inverse of R-Value) – how much an insulation product will conduct, or lose heat. To compare the window to the insulated wall, we need to convert the U-value to R-Value.
A large glazed area in an Australian home typically has a U-value of 6, equivalent to an R-Value of 0.15, whereas wall insulation is expected to have an R-Value of 1.0 to 2.5 depending on the climate zone.
For the Victorian climate, the government authority Sustainability Victoria’s recommendation for wall insulation R-Value is R2.5, with a minimum requirement of R1.5. This means a glazed wall or large window would really struggle to cope with keeping in, or rejecting heat.
A glazed area will leak heat in winter and allow heat into the interior spaces in summer, leading to uncomfortable interior temperatures. The glazing, therefore, needs to be better insulated, like the wall. That means a lower U-value for the windows and glazed doors with a more airtight seal.
While windows are an excellent way to channel natural light indoors, they are much less efficient than insulated walls at keeping temperatures stable and sustainable. Nearly 40% of all energy loss from buildings is through windows and doors, and up to 87% of building heat can be gained through windows.
There are plenty of solutions to improve a window’s efficiency: Consider double glazed panes, reflective low emissivity coatings, insulating gas (argon) between the glass panes, and tightly sealed uPVC frames that reduce air infiltration between the sash and house frame. Unlike aluminium, uPVC does not conduct heat. In fact, uPVC is 1,000 times less conductive than aluminium.
The lower the U-value of the window (and higher its R-Value), the better its insulation performance will be, keeping you warmer in winter and cooler at the height of summer. Most double-glazed uPVC windows in Australia have U-values below 2.2, providing effective and thermally efficient insulation against heat and cold extremes, resulting in more stable, comfortable interior temperatures throughout the year.
According to the CSIRO’s Housing Data Portal, although a growing number of new builds are installing higher performing windows, two-thirds of new builds and apartments in 2019 still had windows installed with U-values higher than 4. This is a matter of concern as the use of these windows lock in poor thermal comfort and energy inefficiency for a long time into the future.
However, the specific reference to uPVC windows for higher performance in some of the free architect-designed plans and base specifications for homes to achieve a minimum 7 Star NatHERS rating in a range of climate zones is a welcome development. Produced by the Australian federal government, these plans can be accessed through the Department of Industry and Science’s YourHome.gov.au website.
For example, using double glazed uPVC windows in the four-bedroomed ‘Telopea’ home – designed for the Melbourne climate – would achieve a top 7.1- or 7.2-Star rating in terms of energy efficiency. Energy efficient windows make your home more comfortable, dramatically reduce your energy costs and help to create a brighter, cleaner and healthier environment.
Given the urgency of addressing climate change-inducing emissions, the higher performing uPVC windows with their energy efficiency benefits have a serious role to play in improving the thermal performance of residential buildings for decades to come – helping mend that ‘wound in the wall’.
