A client recently asked whether they should consider double glazing for their new home in Queensland. Here’s what we advised:
1. Double glazing absolutely assists in keeping heat out during summer, and providing increased insulation during winter, as well as enabling any air-conditioning to operate more efficiently in either season.
2. To help understand the difference between single and double glazing, it is primarily the R-Value that increases:
- An average external wall has an R Value of R 2.2.
- A aluminium-framed single glazed window (including it’s frame) has an R Value of about R 0.15, so heat will travel much more quickly through the glazing that through the wall, as there is less Resistance (R-Value) to the heat flow.
- Double glazing will increase the R value to about 0.3. This doesn’t sound much, but if you think of the average R-Value of a wall that has eg 50% glazing, this change from single to double glazing will increase the R-Value of the combine wall/glazing from R 1.2 to R 1.3, and that will make a difference to the temp. For walls that have more glazing than wall, the gap will widen.
3. In Australia, double glazing is used extensively in cooler climates such as Victoria. It is not as common in the warmer climates, however it is being used more than previously due to a number of factors including increasing use of glazing (as compared to external walls) in dwellings and an increasing desire for more energy efficient housing
4. Double glazing costs around twice as much as single glazing. This obviously depends on manufacturer and exact type of glazing, but if you were comparing clear with clear double, that’s about the average.
5. We would recommend double glazing, despite the additional cost. Note that the additional cost will be offset by a decrease in your energy costs in heating and cooling your dwelling. Not only will there be days where you will not need to artificially heat or cool your home due to the double glazing, but when you do use it, it will operate more efficiently as well. And, you will be contributing less greenhouse gas emissions into the atmosphere. So the cost is a one-off, but the benefits will continue for the life of the dwelling.
6. If you wanted to only use some double-glazing (due to cost), then to get the most benefit, we would recommend using it first in your main Kitchen/Living area, then bedrooms, then other living areas. Using double-glazing in unconditioned areas such as bathrooms, laundry and garage has only a minimal positive impact on energy efficiency, therefore is probably not worth the additional cost for thermal comfort and energy efficiency alone.
7. A common method of Energy Efficiency assessments in Queensland is via the Deemed to Satisfy – Elemental Provisions method (DTS). This method approximates a 5 or 6 Star NatHERS Rating, by examining each building element on it’s own. If you are interested in maximising the thermal performance and energy efficiency of your dwelling, we would recommend having the building assessed via the NatHERS Star rating method. This method takes all aspects of the building into consideration (include aspect, climate zone, building materials, glazing types, design, shading etc), and predicts the anticipated annual energy use from artificially heating and cooling the dwelling. This energy use is then converted to a Star Rating out of 10 Stars (with 6.0 Stars currently required in Qld to pass the Energy Efficiency requirements). With this method, we can assess the dwelling with single glazing throughout, and then see what impact various amounts of double glazing have on the Star Rating. Once the original building is modelled, it is a relatively simple process to see what impact changing any of the variables has on the Star Rating (eg, changing roof colour, increasing wall insulation, increasing eave width etc), giving you valuable information as you finalise the design and select the building materials.
Hope that’s helpful!