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Paint your roof white

A simple effective idea. Cut air conditioning costs in hot climates by 20% by painting your roof brilliant white.  Roofing lasts for about 20-25 years so that the change could be phased it gradually at low cost – only about 15% more than a dark roof.   According to the NYT:

‘The physics behind cool roofs is simple. Solar energy delivers both light and heat, and the heat from sunlight is readily absorbed by dark colors. (An asphalt roof in New York can rise to 180 degrees on a hot summer day.) Lighter colors, however, reflect back a sizable fraction of the radiation, helping to keep a building — and, more broadly, the city and Earth — cooler. They also re-emit some of the heat they absorb….

Before the advent of central air-conditioning in the mid-20th-century, white- and cream-colored houses with reflective tin roofs were the norm in South Florida, for example. Then central air-conditioning arrived, along with dark roofs whose basic ingredients were often asphalt, tar and bitumen, or asphalt-based shingles. These materials absorb as much as 90 percent of the sun’s heat energy — often useful in New England, but less so in Texas. By contrast, a white roof can absorb as little as 10 percent or 15 percent’.

10 comments to Paint your roof white

  • half my roof is red brick tiles and the other half silver/tin channel.

    I wonder what the difference is between silver and say white colourbond?

  • conrad

    “I wonder what the difference is between silver and say white colourbond?”
    .
    Me too. My house gets brutally hot in summer. If there’s a big difference, I’ll do it.

  • John Mashey

    Chu’s LBNL colleague, Art Rosenfeld, is revered as “Dr. Efficiency, and it is well worth reading anything he writes, as he’s had good ideas for decades.

    Also, while white is best, high-reflectivity paints of other colors are worthwhile, with details in some of his presentations.

    As it is in most of California, this seems quite relevant to most of Australia, or in general, anywhere that uses air-conditioning much.

    Note the asymmetry between heating and cooling, especially in urban areas. This shifts the sensible applicability poleward.

    If you heat a building, poor insulation leaks heat into the ambient air, which actually reduces the heating load for nearby buildings.

    When you use air-conditioning, you usually *heat* the surrounding air, which makes nearby buildings burn more energy to keep themselves cooler. Even in relatively undense areas (like downtown Palo Alto, CA), one can feel the heat exhaust from air-conditioners blasting away. Of course, geothermal heating/cooling helps avoid some of this effect.

    Hence, the usefulness of high-reflectivity roofs extends even further poleward than one might imagine, although it probably won’t catch on in Alaska soon, and regulations must be sensible.

  • conrad

    FXH, I looked this up. It looks like the new paints are heaps better and they have even better reflective properties than plain white. There’s also a government subsidy (!) so you needn’t even pay for most of the painting until 2011! Thanks middle-class welfare, I think I’ll get this done sometime.

  • fxh

    Thanks conrad – got any references?

    Is it true there is a subsidy to paint your roof or are you kidding me?

    Painting thinsg is a slippery slope – once you start you have to keep doing it ever 5 years or so. Nope – I’m stickig with my tiles and silver tin.

  • Jacques Chester

    This is pretty well known in a lot of Northern Australia amongst long-time residents. For the same reason white-coloured cars are far more plentiful up there too.

  • Jacques Chester

    It also helps a lot to have proper roof insulation and verandahs wide enough to keep the sun off your walls.

  • conrad

    FXH:

    Yes the subsidy is true — I’ll be getting my house done (I think paint is included — I’ll ask), although I’ll need check if paint counts as insulation (I seem to remember finding that yesterday, although perhaps I was too excited 🙂 — my house is boiling in summer). Here’s the initial link:

    http://www.environment.gov.au/energyefficiency/insulation/homeowners/index.html

    It appears you can choose what you want from a few things (solar etc.)

    There are a fair few different brands of paint around and comments that some are better than others. Insultec seems to be the Australian one and has a 30 year reflectivity warranty. I’ll ask one of the chemists where I work what they think. Try googling “solar paint” and you’ll get heaps of hits — and you can find tables for different types of material too.

  • melaleuca

    Harry “Henry Ford” Clarke:

    You may paint your house any colour you like so long as it’s white 🙂

  • florance

    How about the long buildings and not flat roofs? In Asia roof are mostly not flat so how does that works? And also according to long buildings only the upper floor will be cooler but not the lowers one right?