Every house has windows and doors, and most of them belie the processes involved in terms of choice and design. Today more than ever before a window is not simply an opening in a wall that lets in light and air. Windows play a much more important role in terms of insulation and energy efficiency within the home. They also add to the style of a house.
So the million dollar question if you are building a new home is: what to look for when buying windows?
While cost is always a factor, you should not be driven by price alone. You also need to consider:
- the material used to make the frames,
- the type of glazing used,
- the style and size of frames,
- and probably most importantly, energy efficiency.
Materials for frames
The range of materials used to manufacture window frames is surprisingly varied and includes various types of wood, metal, plastic-type materials and man-made composites. Within each of these categories there are many choices. For example you will find frames made from many different types of wood. They may also be made of mild steel (although this material is not common nowadays because the frames are heavy and tend to rust) or aluminum. They may be made of vinyl or uPVC, or they may be made of a combination of materials; a wooden frame clad with vinyl or aluminum for instance.
Vinyl frames are low maintenance and when made from superior materials, durable. Some are made by an extrusion process, which produces a frame with internal air cavities. Others have a reinforced inner structure, usually wood.
Wood, when used on its own can of course be stained or painted, or simply sealed or varnished, while aluminum frames are normally factory coated, which makes them easier and less costly to maintain. Clad frames also require less maintenance than straightforward wooden frames.
Fiberglass is the newest material to be used to make window frames. They are generally light and strong, and remarkably durable – again provided they are well made. They generally don’t expand and contract with heat and cold as much as some other frames, but they are relatively expensive.
While manufacturers often specialize in certain types of windows and window frames, there are numerous suppliers that offer a range of different types. For example, the Calgary-headquartered Gienow Windows and Doors (www.gienow.com) offers metal clad wooden and vinyl windows as well as straightforward wood and just vinyl frames. Concord Windows and Doors (www.concordwindowstore.com) in Toronto sells PVC and wood windows.
There are different types of glass used for glazing as well as different ways that the glass is installed. For instance tough tempered glass may be used to withstand breakage, or laminated glass which will shatter in such a way that it doesn’t become a risk of injury. National Building Codes all over the world govern minimum standards and specifications of glass including the type of glass and thickness that may be used in any particular sized window, and how it must be fitted. Safety glass is usually specified for patio doors and windows where there is any danger of human impact, either accidental or deliberate.
In Canada, windows are usually either double-glazed (with two layers of glass separated with a spacer) or triple-glazed (either with three layers of glass or two layers with low-emissivity film between them).
Style and size of frames
There is a vast choice when it comes to size and style of window frames, ranging from small fixed windows that do not open, to enormous sliding windows with a single pane of glass, or small cottage windows that are divided by secondary frames known as mullions.
Hinged windows are probably the most common type, although they may be hinged to swing from side to side or at the top, or even at the bottom. Sliding windows are popular because they don’t take up space. Some are made to slide vertically while others slide horizontally. However they are potentially the least energy efficient of all windows types because they are prone to water and air leaks.
When we consider the energy efficiency of windows, it is not only their ability to keep out the cold that we need to think of – although in cold winter countries like Canada, this is paramount. We also need to consider the ability of windows to block out heat and the harmful UV rays of the sun. Their ability to transmit visible light is another factor that we need to think about, as is their ability to prevent air from escaping in or out of the window.
As the Canada Mortgage and Housing Corporation (www.cmhc-schl.gc.ca/) points out, performance standards and new technologies have changed significantly during the past two decades and so it really is important to know what to look for when buying windows for your home.
Wood frames, being made from a natural material, have high insulating properties, although the frame must be well made otherwise it won’t necessarily be airtight. Clad wood frames have similar natural insulating qualities and need less maintenance than solid wood that isn’t clad.
Aluminum frames are strong and undeniably more durable than wood, but they do conduct heat. For this reason, the National Building Code of Canada insists on them being made with a thermal barrier inside the frame to reduce heat loss and condensation. This should be made from rigid foam, polyurethane or from wood. Like wooden frames, if they are not well made, both water and air can leak through joints – particularly badly mitered corner joints.
Vinyl frames are regarded as being very good when it comes to insulation.
The type of glazing used also affects insulation. For example, air trapped in double-glazed windows aids insulation. Triple-glazed windows, though, are considerably more effective in terms of insulation. They are also effective when it comes to reducing noise from outside. But triple-glazed windows are heavy and more expensive than those that are double-glazed.
The low-emissivity film used for some triple-glazed windows may be used on the inside of double-glazed windows to stop heat from escaping. The advantage of this is that the window is lighter than one that is triple-glazed and not as expensive. This film also reduces condensation on windows and gives some protection from the UV rays of the sun.
A fairly recent innovation in window technology involves replacing the air in double- or triple-glazed windows with some sort of dense, inert gas. The gas has a much higher insulating ability and also lower thermal conductivity. While argon is the most usual gas used, Marvin Windows and Doors (www.marvin.com/windows/new-window-products/) recently introduced a product that uses krypton gas that has even better thermal qualities than argon.
Overall, this is what to look for when buying windows that are energy efficient:
- the U-factor for insulation – the lower the number the better,
- the SHGC (solar heat gain coefficient) for blocking out the sun – the lower the SHGC the better,
- the VT (visible transmittance) factor – the higher the value the more visible light you will see,
- the R-value that measures heat loss – the higher the better, with R-5 being optimum.
Remember that windows can account for as much as 30% of the heat lost from a house. That’s according to Natural Resources Canada (www.newhomes.nrcan.gc.ca) which promotes energy efficient products, including ENERGY STAR windows.
Supreme Windows in Calgary (www.supremewindows.net) is one that promotes added hard coat Low-E glazing options. Meridian Windows & Doors (meridianwindow.net), which operates out of Calgary and Toronto, specializes in ENERGY STAR vinyl products and aluminum windows.
One of the world’s largest window manufacturers, Jeld-Wen Windows & Doors (http://en.jeld-wen.ca) makes wood, vinyl and aluminum clad windows. In 2010 they became the first Canadian door and window manufacturer to promote ecoENERGY Retrofit Homes in the federal government’s energy efficiency program. This program allows homeowners to get grants once energy advisors certified by Natural Resources Canada have done an official assessment.