Windows for warmth

Replacing old windows is a great way to improve air quality and your health. Healthy Home Cooperation Director Damien McGill tells us how to improve the thermal performance of our windows.

No matter how you look through it, windows are holes in your thermal envelope, the duvet that cocoons you in the sanctuary of your abode.

We need windows to let light in, and doors for the summer indoor-outdoor flow, to and from the barbecue. So how do we improve their thermal performance?

The first thing we can do is to stop using solid aluminium window frames. Aluminium is one of the most conductive materials on the planet. Think what else aluminium is used for; wiring and cookware. Aluminium is nearly 2000 times more conductive than timber!

That condensation on your window frames is caused by the moisture in the air generated by you just being you; living, breathing, cooking and washing, liquifying on the cold window frames. They are cold because the aluminium is at a similar temperature to the outside air. Think dew, but inside.

Standard aluminium double glazing has no place in a Healthy Home. So, what can be used instead?

I’m in the throes of a multi-year, multi-unit ‘SuperReno’. I’ve replaced the original double-glazed aluminium windows on the south elevation of this project with triple-glazed PVC. Straight away, my south-facing office is warmer than my north-facing master bedroom, and the condensation is now on the outside of these new PVC units.

You may have heard of something called thermally broken aluminium. This is where the central core of the window is replaced with a much less conductive plastic material. In high quality thermally broken aluminium windows, the aluminium primarily becomes a decorative, low maintenance cladding.

Then there is wood. Remember wooden windows? All pre-1970s houses originally had wooden windows. Modern timber windows are a thing of engineering beauty, being airtight with multipoint locking systems.

Oh – please don’t forget to add some glass! There is some fancy energy-saving, see-through stuff out there. Aim for low-E (emissivity) argon gas filled units with warm edge spacers.

I strongly advise against replacing single glazed timber with standard double-glazed aluminium. When upgrading timber windows, it’s better to replace the whole window to make the opening as airtight as possible. If you’re on a budget, replace a window or two per year and make sure all of the windows are recessed, not sitting out in the cavity.

To find out more about our guidelines for windows and doors, have a look at The Healthy Home Design Guide.

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