A Canberra house can feel perfectly comfortable at nine in the evening and distinctly unpleasant at six the next morning. The heater has been off for a few hours, frost is sitting on the lawn, and a film of water is running down the inside of the bedroom glass. This article explains where that heat actually went overnight, and why the windows, rather than the walls or the roof, are almost always the place it left from. It also covers what the condensation on your glass is measuring, what changes when a window is built differently, and what to check in your own home this winter.
How cold Canberra actually gets
Canberra is inland and sits at elevation, and that combination produces cold nights. The city records the coldest winter minimums of any Australian capital. Through June, July and August, overnight temperatures below zero are routine rather than remarkable, and frost on the grass in the morning is simply part of the season. Dry inland air also sheds heat quickly once the sun goes down, so a pleasant afternoon can turn into a hard freeze by dawn. The Bureau of Meteorology holds the long term record for the city, and it is worth looking up the figures for your own area.
The contrast with coastal Sydney matters, because much of the window and heating advice published in Australia is written with Sydney in mind. Sydney has the ocean beside it, and the water keeps overnight temperatures up. A window that performs acceptably through a Sydney winter is being asked to do far less work than the same window in Weston Creek or Queanbeyan at five in the morning.
Why windows are the weak point
Think about what an external wall is actually made of. Brick or cladding on the outside, a cavity, insulation batts between the studs, then plasterboard on the inside. Four or five layers, at least one of which exists purely to slow heat down. Now think about what a window is: a sheet of glass a few millimetres thick, held in a frame. There is no insulation anywhere in that assembly. A window is a hole in your insulated wall, covered by the thinnest material in the building.
Heat always moves from the warm side to the cold side, and how fast it moves depends on what sits in its way. Glass offers very little resistance. A single pane is effectively a thin, highly conductive panel separating a heated room from a freezing night, and it keeps handing your heat outside for as long as there is a temperature difference across it.
The frame is the part most articles skip past. Aluminium is one of the best heat conductors in common use, which is why saucepans and computer heatsinks are made from it. An aluminium window frame runs continuously from the inside of your home to the outside, so whatever warmth touches the inner face is carried straight through the metal and released into the cold.
Builders call this thermal bridging: a material that carries heat easily, running uninterrupted from the warm side of a building to the cold side, bypassing the insulation around it. In a house with single glazing in aluminium frames, the glass and frame together form one continuous path out, and the frame takes up a meaningful share of every opening. That is why upgrading the glass alone so often disappoints: you improve one half of the path and leave the other half conducting exactly as before.
What the condensation is telling you
Air holds moisture, and warm air holds more of it than cold air. The dew point is the temperature at which the air can no longer hold what it is carrying. Indoor air picks up moisture constantly, from showers, cooking, clothes drying inside, unflued gas heaters, and the people breathing in the room. When that air touches a surface colder than the dew point, the moisture leaves the air and forms water on the surface.
So the water on the inside of your window in July is a measurement. It tells you the inner face of that glass is sitting below the dew point of the room, which means it is running close to the outdoor temperature. Condensation is a symptom of heat loss, not a fault in the window. Wiping it up each morning deals with the water and does nothing at all about the reason it is there.
Left alone across several winters, that water does real damage. Timber frames and sills absorb it, swell, and eventually rot, and paint lifts from the inside face first. On reveals and in the corners of architraves, repeated wetting feeds mould, which comes back every winter no matter how often you clean it off.
What a sealed double glazed unit changes
A sealed unit is two panes of glass held apart by a spacer around the edge and sealed together as a single component. The gap between the panes is the working part. It is filled with argon, an inert gas that conducts heat less readily than ordinary air, so the cavity resists the heat trying to cross from the inner pane to the outer one. If you want the details of how a sealed double glazed unit is built, it is worth understanding before you compare quotes, because construction varies between products.
The other half of the performance comes from a low emissivity coating, a microscopically thin metallic layer applied to one of the internal glass surfaces. It lets visible light through but reflects radiant heat back towards the source, so warmth radiating off your heater, your furniture and your body is returned into the room instead of passing out through the glass.
Then the frame has to change as well. A multi-chamber uPVC frame is built from sealed hollow chambers running the length of each section, and the still air in those chambers does not carry heat the way solid metal does. This is the part worth being careful about when you get advice: fitting a high performing sealed unit inside an existing aluminium frame leaves the bridge exactly where it was. The glass gets better, the metal keeps conducting, and the condensation often simply moves from the glass to the frame.
Is triple glazing worth it in the ACT?
Canberra is one of the few places in Australia where triple glazing can be justified on performance rather than novelty. In a mild coastal climate, a third pane adds cost and weight and very little comfort. In a climate with sustained sub-zero nights, the extra sealed cavity does measurable work, so ACT homeowners are not wrong to ask the question.
Two cautions, though. The first is that triple glazing is a step beyond a well-built double-glazed window, not an alternative to one. If the frame is still conducting, a third pane does not fix it. You have improved the best-performing part of the assembly and left the worst alone, so the frame comes first and the third pane is a decision after that.
The second is weight. Three panes are heavier than two, which affects hardware, hinges and the way large sliding panels run. It is a sensible upgrade for a bedroom on the cold side of the house, and rarely the obvious default for every opening.
What to look at in your own house this winter
Pick a genuinely cold morning, before the heating has been running long, and work through this.
- Run the back of your hand slowly around the edge of each window, where the frame meets the wall and along the join between the opening sash and the fixed frame.
- Start with the rooms you use least. Unheated and south-facing rooms show the problem most plainly.
- Look at where the condensation sits. Water on the glass alone tells you the glass is cold. Water on the frame as well, or frost on the metal, tells you the frame is conducting and that a glass-only upgrade will not solve it.
- Check sills and the bottom of the reveals for staining, swelling, soft timber or lifting paint.
- Photograph each window from inside, in daylight, with the whole opening in the shot. Note the frame material and whether it slides, opens outward or is fixed.
Heating a house is mostly about what it lets out
Heating a Canberra home through winter is mostly a question of what the house lets out rather than how much the heater puts in. You can run a bigger heater for longer, or you can stop the heat leaving through the thinnest and most conductive part of every external wall. The windows are where that decision gets made, and the frame matters as much as the glass.
If your windows are the weak point, we supply and install double glazed uPVC windows and doors across Canberra and the ACT. Book a free measure and quote.