• Reine Williams

The basics of windows

Windows have come a long way since the majority of homes in Canberra were built. Below is a basic outline of the most common window systems you will find in Canberra today.


Glass systems

Single glazing. You probably grew up in a house with it, and if you are looking at renovating your home... you probably still have it.

Double glazing. Two panes of glass with an air gap. This gap provides insulation to slow heat transfer, it also helps provide acoustic insulation and improves the strength of the glass.

Triple glazing. Three layers of glass = more insulation. Very popular in Europe, slowly creeping into the Australian market. Interestingly, can have a negligible effect on a homes energy rating if the home has been designed to solar passive principles and has optimal glazing (ie. the increase in the insulative properties does not outweigh the reduced solar heat gain - see those items below).



Glazing treatments

Argon. This gas can be added between the layers of glass. It slows the conductance of the air gap, therefor increasing the insulation value of the glazing.

Low-E coating. Think one-way shop glass - the low-e coating allows the beneficial heat in from outside, but then reflects it back rather than letting it escape. You can often see this as a blue-grey tinge to the glass.


Frame systems

Aluminium. The most common and basically a frying pan when it comes to conductance. Whatever the temperature outside = inside.

Thermally broken Aluminium. Internal and external frames are separated by a rubber (polyamide) seal to reduce the conductance. They perform much better than standard aluminium, and can be different colours inside and out.

Steel. Yep, they exist. If the frames look really fine compared to typical windows chances are they are steel. They actually perform reasonably well as the steel is 4 x less conductive than aluminium.

Timber. Beautiful, high maintenance. Thermally one of your best options... but see previous sentence.

uPVC. Unplasticized Polyvinyl Chloride = plastic. Thermally awesome, common in Europe and smooth to operate. Have thicker frames (70mm) and sashes (another 70mm) which need to be considered in window design to prevent awkward proportions.


Operations/ Components

Sliding. The typical - one side is fixed, the other slides.

Awning. Hinge at the top, winder at the bottom.

Casement. Like a mini-door, hinge on one side, winder or manually pushed out on the other side. Can be arranged to swing inside or out.

Double hung. Like at your grandmas house. A top and a bottom pane of glass that move independently up or down. Can also come with a moveable bottom hung or top hung, with the other half fixed.

Tilt and turn. Handle on one side, you twist up to lock, middle to swing inwards, down to tilt inwards (hinge at bottom). Fabulous, secure, don't work with traditional curtains or blinds as windows swing inwards (work great with up down honeycomb blinds mounted to each pane - like nordicblinds.com.au).

Transoms. Horizontal bars (often fixed), common in full height windows where top portion is sliding window.

Mullion. Vertical bars.

Colonial bars. Additional decorative mullions and transoms.


Performance

U-value. This is the system of measuring the conductance of a window. Less = better thermal resistance. The glazing and the frame will have different u-values and the ratio of frame: glass in the window affects the value.

Fun fact: U= 1/R. So if you have been looking at putting R2.5 batts in your walls, that is the equivalent to a U-value of 0.4. Amazing triple glazing might get a U-value =1.3, which gives an R-value of 0.77... [summary: no matter what, windows are holes for your homes energy efficiency.]

SHGC. Solar Heat Gain Co-efficient. This is the heat from the sun that can pass through the window in winter - the basis of solar passive design. Higher = better. In Canberra, with cool sunny days SHGC can be extremely beneficial to help heat a home with free energy from the sun.


Further reading

WERS. Window energy rating system - technical explanations of the above: awa.associationonline.com.au/werscontent/about-wers

Your Home. Free government resource database for designing or building your own home sustainably:

https://www.yourhome.gov.au/passive-design/glazing