Ask G

Ask G: Effects of double-glazing

Double-glazing can help insulate your home, but can it impede other passive heating options?

We're planning an eco-renovation and want to include a polished concrete floor to capture the winter Sun and passively heat the area, with floor-to-ceiling windows on the Sun-facing wall. Would double-glazed windows reduce the amount of sunshine that could enter to heat the concrete floor in winter? We thought double-glazing would help with insulation, but want to maximise the warmth from the Sun in winter.

Jane, SA

Window looking out to garden path

Capturing the sunlight will help to keep you warm in winter, but you won't like it in summer unless you factor adequate summer shading into your plans!

Credit: Wikimedia

- Advertisement -

Firstly, you're doing a great thing environmentally by choosing to eco-renovate an existing house rather than bulldozing it and building a flash new one from scratch.

It's a great idea to capture the free heat from the Sun, and having a Sun-facing lounge gives you a good opportunity to do so, provided it's not overshadowed by large trees or neighbouring buildings.

Assuming the glass isn't tinted or reflective, double-glazing won't noticeably reduce the amount of radiant heat-producing sunlight pouring through your windows.

The level of insulation is given as an 'R-value' (the higher the number, the greater the insulating effect). A single pane of glazing has an R-value of 0.14. Double-glazing brings the window area's R-value up to 0.31.

Curtains will also provide insulation, as well as privacy, potentially bringing the R-value of the covered, double-glazed window up to 0.45 for conventional curtains with pelmets. Window frame materials can also have an effect.

Capturing the sunlight will help to keep you warm in winter, but you won't like it in summer unless you factor adequate summer shading into your plans!

External shading is the most effective way to keep out summer heat, and options include an eaves overhang, sail or shade cloths that can be removed in cooler months, awnings and pergolas.