Windows come in a number of different frame and glazing types. By combining an energy-efficient frame choice with a glazing type tailored to your climate and application, you can customize each of your home’s windows.
TYPES OF WINDOW FRAMES
Improving the thermal resistance of the frame can contribute to a window’s overall energy efficiency. There are advantages and disadvantages to all types of frame materials, but vinyl, wood, fiberglass, and some composite frame materials provide greater thermal resistance than metal.
ALUMINUM OR METAL FRAMES
Although very strong, light, and almost maintenance free, metal or aluminium window frames conduct heat very rapidly, which makes metal a very poor insulating material. Metal frames should have a thermal break — an insulating plastic strip placed between the inside and outside of the frame and sash.
Composite window frames consist of composite wood products, such as particleboard and laminated strand timber. These composites are very stable, they have the same or better structural and thermal properties as conventional wood, and they have better moisture and decay resistance.
Fiberglass window frames are dimensionally stable and have air cavities that can be filled with insulation, giving them superior thermal performance compared to wood or uninsulated vinyl.
Vinyl window frames are usually made of polyvinyl chloride (PVC) with ultraviolet light (UV) stabilizers to keep sunlight from breaking down the material. Vinyl window frames do not require painting and have good moisture resistance. The hollow cavities of vinyl frames can be filled with insulation, which makes them thermally superior to standard vinyl and wood frames.
Wood window frames insulate relatively well, but they also expand and contract in response to weather conditions. Wood frames also require regular maintenance, although aluminium or vinyl cladding reduces maintenance requirements.
New homes or major renovations
The building code now lays down minimum requirements for new windows – that’s almost certain to mean double-glazing.
If you have first blocked draughts, insulated your ceilings, under the floor, and maybe the walls and you still feel cold, the windows will be the cause of most heat-loss in winter and gain in summer. How much is lost (or gained) depends on where you live, the type of windows you have, how big they are, and the direction they face.
Double glazing will take many years to pay for itself through reduced heating or cooling bills so it is to be viewed as a long term investment. But research has shown that secondary-glazing of existing windows can be just as effective and cheaper – sometimes a lot cheaper.
A well hung set of curtains can be just as effective as double-glazing and much more cost effective.
Above: secondary glazing
Secondary-glazing creates an air-gap by inserting a second pane of glass or other clear sheet behind an existing windowpane.
Above: double glazing
Double-glazing has 2 panes of glass spaced apart by a gap containing air or argon gas. This is then sealed to form an insulated glazing unit (IGU).
IGUs can have different insulation ratings. These depend on:
- whether standard or low-emissivity (low-e) glass is used
- the distance between the 2 panes
- the type of gas (air or argon) in the gap.
The edge-seal of an IGU must not be allowed to remain wet. That means these units must be installed in a frame that allows free drainage of water.
Once the original glass has been removed the unit can be fitted either directly into new window frames or retro-fitted into an existing window frame.
This is not popular in New Zealand as our climate does not justify its use. Triple glazing is used mostly in Northern-Europe and North America, where winter temperatures get much colder than here. “Triple” glazing uses 3 sheets of glass to create 2 air-gaps. Triple glazing needs an extra-wide frame and creates a heavy window.
Before you get double-glazing installed:
- Insulate your ceilings and under the floor (plus walls if practical) before considering double-glazing.
- Use curtains – and make sure they have good seals at the top and bottom.
- Try temporary secondary-glazing first. It may be all you need.
- Look at options such as low-e glass and argon gas between the layers if you want to install permanent secondary-glazing or new double-glazing
- Thermal-aluminium, wooden or PVC joinery is more efficient than standard aluminium frames.
- Make sure you get several quotes for whichever double-glazing system you’re considering.