Any window is only as good as the frame that holds it in place, and double glazed windows are no exception to the rule. In fact, double glazed windows place greater demands on frames than ordinary windows, since the extra weight of the second pane of glass places greater strain on the weight-bearing capacity of your frame. The frames must also be durable enough to resist wear and tear that might allow gas to escape the space between the two panes of glass, as this space is filled with the heat-insulating noble gas argon -- allowing this gas to escape can dramatically undermine the heat insulating properties of your double glazing.
As you can imagine, then, choosing the materials your double glazing frames are made from can make the difference between decades of faithful service and a cracked, draughty disaster. Fortunately, you have a number of choices when it comes to framing materials, and three frame materials in particular are particularly well suited to double glazing framing.
The traditionalist's choice, wooden frames add a touch of old world charm and sophistication to any home and will complement practically any style of architecture. If you are purchasing double glazing to lower your heating and/or air conditioning bills, wood can be an even more attractive choice, due to the excellent heat insulating properties of most woods. This means that hot or cold air trapped indoors by the glass will not escape via conduction through the frames, as is sometimes the case with uPVC or metal frames.
However, wooden frames are not something you can just fit and forget, and many wooden frames will fall victim to rot and insect damage without regular inspections and maintenance. Thankfully, Some choices of wood, such as tropical hardwoods like ipe and mahogany, are more naturally resistant to rot, and various stains and treatments are available to prolong the life of your wooden frames. Most importantly, if you choose wooden frames, be sure to choose a wood strong enough to support your double glazing for many years -- some softwoods commonly used for window frames lack the required strength to support double glazing.
Unplasticised polyvinyl chloride, commonly known as uPVC, is a plastic polymer ideally suited for window framing, and its properties make it an excellent choice for double glazing frames. uPVC is more than strong and tough enough to withstand the weight of double glazing, but its greatest strength is its resistance to practically anything nature can throw at it. uPVC frames will endure many years of rain and wind without cracking or perishing and require minimal maintenance. They are also invulnerable to fungal decay and insect attack, and since they are generally sold in a prefabricated unit with the glass already fitted, they are swift and easy to install.
All of these properties make uPVC a very attractive choice -- and therein lies the problem. The popularity of uPVC window frames means they lack any particular aesthetic distinctiveness, and the drab, white plastic may not be to everybody's taste. This is particularly true for people fitting double glazing to older, more traditionally styled homes, as the modern appearance of uPVC can clash rather badly with traditional building materials. This problem can be allayed somewhat with coloured paints and coatings, but the frames will still retain their smooth, synthetic look and feel up close. uPVC may also be an unsuitable choice for homes in particularly hot and sunny areas, as it tends to expand under intense heat, shortening the usable lifespan of your frames.
Commonly seen in industrial and commercial buildings, aluminium window frames are the last word in strength and durability, making them the frame of choice for larger double glazed windows and picture windows. Aluminium is also aesthetically versatile and can be painted and coloured with countless paints and treatments to achieve the aesthetic you desire.
However, aluminium windows are generally very time-consuming and difficult to install, and as a result they can require a significant monetary investment. They are also vulnerable to oxidisation caused by moisture and general exposure to the elements, and while aluminium oxidisation's effects are merely superficial, steel fittings placed within the frames to add strength are particularly vulnerable to rust.