Ask G

Ask G: White roofs

Should we paint our roofs white on top?

Some years ago when I was visiting Australia, from time to time I would say not-so-nice things about people who had dark-coloured roofing material in this hot climate. Now that I am living here I am using many times more power heating my house in winter than cooling it in summer, therefore I was starting to think that dark-coloured roofs were the best – until I read an article about how we should paint our roofs white. So can you please enlighten me and others: Is it because I have a stone-walled house here in South Australia?
- Brian Polkinghorne, via email.

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A white roof (or darker one, for that matter) is not an energy bill silver bullet. There’s interplay between the design and materials of the house itself and its suitability to the local climate that results in your home’s heating and cooling needs. Although our country has a reputation for sunshine and surf, the Building Commission of Australia defines eight different climate zones for building considerations.

Unlike places like Northern Europe or Canada, very few of our homes have snow piling up at our doors in winter. We’ve been able to get away with lighter construction, so our homes aren’t typically as well insulated and airtight. But many regions still get cold winters and/or cold nights. Your experience of higher winter bills is not uncommon or unexpected in southern SA.

To make homes more energy efficient, architects and builders incorporate multiple measures, including passive solar design (using free heat from the sun), insulation, thermal mass (the ability of some materials to store and re-release heat) and the placement and efficiency of windows. For a summary of design considerations by climate zone, visit the Your Home website (www.yourhome.gov.au) and click on ‘Design for Climate’.

Stone has a relatively high thermal mass, but is a poor insulator, so your stone walls may let heat escape. I can’t be more specific without seeing your home, but I’d recommend having a qualified home energy auditor assess your house to provide some site-specific advice. Roof colour is only one consideration, and there may be other measures that would make a greater difference.