Passive Design Principles - Glazing


We all know windows are one of the most important design elements to consider when building an eco friendly home. Did you know your home can lose up to 40% of it’s heating energy in winter and gain up to 87% of unwanted heat in summer through windows alone? Choosing windows that optimise your home's thermal performance can make your home more comfortable as well as drastically reduce your energy costs and the cost to the environment.

Double or even triple glazed windows are standard features of our energy efficient home designs, in today’s post we are going to look into the impact of glazing in the home and the technology available to maximise energy efficiency.

Contrary to popular belief, windows glazing is not a ‘one size fits all’ solution but when used correctly glazing can significantly increase your homes energy efficiency.

Some things you should consider before choosing glazing are:

  • climatic conditions in your location — temperature, humidity, sunshine and wind
  • building design — the orientation, form and layout of the building
  • building materials — the amount of mass and insulation
  • the size and location of windows and shading
  • thermal properties of glazing systems.

Reference -

Glass is an excellent thermal conductor, meaning it is particularly poor at resisting temperature. Double or triple glazed windows work to combat this by holding a barrier of air or gas which acts as a barrier between the outside and inside. Because air is a poor conductor of heat, much less heat is lost through the window. We also use low e films, which help deflect the warm air in the inside of the house back away from the window.

Glass is not the only important element of a window, the frame also plays a pivotal role in insulating the home. Traditional aluminium window frames are strong, weatherproof and low cost, but they are also an excellent thermal conductor. Timber frames work much better than aluminium but have the downside of being high maintenance, limited in colours and expensive. In our 7, 8 or 9 Star homes we use thermally broken frames. Basically the aluminium frame is broken up with polyamide or polymer, which acts as an insulating barrier, reducing the energy (hot or cold) via the frame. You can check out thermally broken frames at most window stores, they will show a standard aluminium frame that is touching a cooling element which a temperature gauge measures, they then show a thermally broken frame which is touching the same cooling element but sits at or very near room temperature. Thermally broken frames also help prevent condensation, learn more here -

Outside of double, triple glazed and thermally broken frames, window film is another option. Window Films are basically a sheet that gets applied to the inside of the glass and there’s stacks of different brands, types and uses. The quality of the film and the use are the two key factors to getting energy gains from window film. The most effective use we have found is for west facing windows that take a beating from large amounts of hot summer sun.

Exterior shading is always going to be better than window film as you are breaking the heat before it hits the glass, so trees, blinds or awnings are ideal here. In a situation where this is not possible, for those west facing windows you can use a high blockout film to reduce the solar heat gain by up to 80%. The films can also cut UV rays. Most films claim to prevent 99% of UV rays, so this can help in baby/kids rooms or even to prevent furniture or timber floorings from fading. There are now also ‘winter’ films on the market, that deflect indoor heat so it is retained inside the home. These films still let light in. It’s basically a compromise between light and solar heat, so the darker films can cut huge amounts of solar heat gain and give you more privacy during the day, whilst the lighter films allow more light to pass through but won’t cut the same amount of heat. Window film is commonly used in residential apartments where there might be a lot of glass and body corporates won’t allow exterior shading or the height of the building prevents it.
I hope you enjoyed this post, Dennis.