Why are double-glazed windows here in Australia so important?
The word on everyone’s lips these days is double glazing for windows, but in Australia it seems to be a foreign concept. The recent focus on energy efficiency in this country has moved a rather stubborn marketplace — in which double glazing was really only used for acoustic performance or the snow regions of the country (usually by choice) — to a requirement for energy-efficient windows. So why would you need cold-country technology in a temperate country? Energy efficiency works both ways: heating and cooling. What performs to keep extreme cold out of a building also works to keep extreme heat out of a building and keep cold air in. No matter which way, less energy will be used to heat or cool a home, and windows play a much larger role in the overall energy efficiency of a home than normally credited.
Double glazing and uPVC
In Europe, the UK and US, the move to double glazing for energy efficiency started between 35 to 45 years ago, and uPVC slowly increased market share to the stage where they are now the dominant window type used. uPVC windows are specifically designed for double glazing and the excellent material properties make them a superior window system.
The next question is usually, “What is uPVC? Isn’t it just plastic/vinyl?” While uPVC windows are the norm in Europe, they are rare as hens’ teeth in Australia and the marketplace has no concept of what they look like. This seems to lead people who have not travelled overseas to think “cheap plastic” windows, which is quite far from the truth. PVC is an amazingly diverse material and is used for anything from building materials to clothing and woven furniture. Polyvinyl chloride is really a thermoplastic polymer and, depending on the additional of plasticisers, can be either rigid or flexible.
The u in uPVC for windows and doors means unplasticised (does not have any plasticisers added to make it flexible), making it a rigid and dense material with excellent biological and chemical resistance. After being used in Germany for windows since 1954, the modern uPVC frame production includes vast improvements in impact modifiers and stabilisers meaning that the windows are tough, do not discolour, require only cleaning for maintenance, do not corrode, rot or become chalky and are very poor conductors of heat. In a word, ideal.
Modern uPVC windows are not “cheap plastic” but are usually made from profiles with multiple chambers for added thermal performance and have a nice glossy surface finish similar to modern flashy fibreglass boats. They are usually made from profiles 60—70mm thick and so have a solid, “chunky” look which can be a very modern sleek white, or a classic wooden look which is difficult to tell from the real McCoy. Damage or scratches can be buffed out, holes can be filled and made virtually invisible, but in reality the modern uPVC is a very tough material. Forty years of experience has created a beautiful and functional window for tough climates.
While uPVC is an excellent material it does move in response to temperature change and is structurally not as strong as other window materials such as timber and aluminium. This has been overcome by installing steel or aluminium reinforcing within the chamber of the profile. Since the windows are welded together, this metal is not exposed to the external environment; however, the steel is normally galvanised. As in the case of wooden windows, dark colours should be avoided in Australia to avoid excessive heating from the high UV levels found here.
Operation of uPVC windows
Window profiles in Europe are designed for ease of manufacturing and the European hardware has been developed to the point where the sealing and security of these windows is unsurpassed. In Europe the tilt-and-turn system has become the norm but it is completely foreign to Australians who are used to good old English double-hung or sliding windows. Tilt-and-turn windows are superior for ventilation options and cleaning from the inside of the building. In tilt mode, the top of the window tilts into the room so the cool air near the floor is not moved out of the building, but rather the hot air up higher is vented.
This mode is your normal opening mode, and completely secure in the open position. However, by moving the handle into the next position the window can be fully opened like a hinge door, allowing for additional venting or simply to facilitate cleaning the glass on the outside from the inside of the building. Sliding doors, balcony doors and French doors have this same tilt-and-turn mechanism, allowing for secure ventilation at night from your doors as well as windows.
The next question is usually about flyscreens or blinds, and in a country where there is little experience with tilt-and-turn windows, it is a valid question. The flyscreens are simple: they mount on the outside of the window in the same way as a double-hung or sliding window. Blinds are a bit trickier but your window manufacturer can run through the various options for you. Blinds are simply mounted on the sash (rather than the frame) so that they move with the sash. Another alternative is to use a deep reveal and mount curtains on the wall, allowing the window to tilt open.
For the less adventurous there is an excellent tilt-and-slide system available with the same sealing properties as the tilt-and-turn available at additional cost, but far superior to your standard sliding windows which rely on brush seals (which keep bugs out but not air). In this system the sash scissors directly out from the frame and then runs effortlessly on a transport “buggy”. The tilt option remains as well, so your sliding door can be left securely in tilt mode for added ventilation. There are limitations on sizes for this system and without a turn option you will have to climb a ladder to clean the window.
Double glazing needs good seals
The double glazing in uPVC windows is usually a 24mm overall thickness, allowing for a larger air gap between layers of glass; therefore uPVC is ideally suited and infinitely flexible to accommodate various overall glass thicknesses. The increased air gap between the panes improves the thermal and acoustic performance of the unit. In cold climates an inert gas such as argon is used instead of air between the glass panes to avoid windows fogging since the dramatic temperature difference inside to outside creates a dewpoint where water condenses. Argon has the added benefit of improving thermal and acoustic performance but, in reality, few places in Australia require the added expense.
Now the best double-glazing options can be overcome easily by poor seals on the window frames, allowing outside air in or inside air out and again uPVC windows excel in this area. Seals are used in two places: on the inside sash to frame connection point as well as the outside sash to frame connection point. The hardware is installed in between the two seals and has a series of locking points all around the sash to pull the window in tight, creating some of the lowest air infiltration levels for any window available. This allows the double glazing to do its job without being compromised by air infiltration. In Europe, buildings with these windows actually require manual ventilation because they are so well sealed.
Normally, the glazing bead, which snaps into the profile, is installed from the inside to provide increased security and burglar resistance with the added bonus that glass replacement can be achieved from the inside of the building for upper-storey or difficult-to-reach windows. The glazing beads can be removed and replaced multiple times as long as you know the trick to removing them.
Lead-free uPVC: the environmental choice
In the early 1990s, Europe began to remove one of the stabilisers used in uPVC window profile manufacturing: namely, lead. A replacement stabiliser was developed — calcium/zinc — but the difference in extrusion properties meant that the changeover to lead-free uPVC was very costly to avoid surface finish difficulties. One company in Germany moved to completely lead-free profile production in 1994 and at the time was known as Plusplan. When the rest of the industry did not follow, its investment was a heavy burden, but as Europe moves to completely lead-free uPVC the phoenix arose again as Plustec GmbH and is now the most experienced producer of quality leadfree uPVC profiles.
The ideal double-glazed window
For an exceptionally good-looking, long-lasting (some windows in Europe are now 40 years old and still look great), low-maintenance, economical and highly energy-efficient window, it is difficult to go past uPVC for a double-glazed window system. It is really worthwhile to find a supplier in your area and look at them first before you blindly judge them as “cheap plastic”. The rest of the world has moved this way and Australia will soon follow. Plustec Pty Ltd is the Australian distributor of Plustec profiles and the manufacturer of Plustec double-glazed windows and doors.
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