Reroofing the Advanced Light Source at Lawrence Berkeley Lab. Photo: Lawrence Berkeley Nat’l Lab/Roy Kaltschmidt

While much of the coverage of energy issues faces on big geopolitical or technological challenges (Reduce dependency on foreign oil! Make solar as cheap as coal!), some of the biggest gains in energy efficiency can come from seemingly innocent actions.

Three years ago, then-candidate Barack Obama inspired ridicule from some quarters by suggesting that checking for proper tire pressure would save as much oil as new offshore drilling could produce (turns out Obama was wrong: properly inflated tires probably save three times as much oil as new offshore drilling could produce).

Another strikingly simple approach is to encourage so-called “cool roofs”. White or reflecting roofs replacing dark roofs, can offset large amounts of carbon dioxide (a recent LBL study suggested that two years of global carbon emissions could be mitigated). The idea was pioneered by LBL’s Art Rosenfeld and Hashem Akbari, and last year Energy Secretary Steven Chu (a former director of LBL) announced new policies to implement cool roof technologies on Department of Energy facilities.

Workers are now on one of the most visible roofs in Berkeley — the 90-foot dome of the Advanced Light Source (ALS) facility at LBL. While the ALS was only completed in 1993, the dome dates to the 1940 cyclotron building at the Lab. The project, which will replace all the shingles on the 20,000 sq. ft. dome, will take five weeks because no more than four workers are allowed on the dome at any one time for safety.

According to LBL’s Julie Chao, the ALS is being reroofed with Owens Corning Duration Premium Cool Shingles, which have a solar reflective index (SRI) of 30, higher than Secretary Chu’s mandated 29 for DOE buildings. The SRI derives from a formula devised by LBL, incorporating both the solar reflectance and the thermal emittance of a product.

LBL researcher Haley Gilbert, quoted by Chao, said that the solar reflectance of the shingles is around 25%, compared to 5% for a standard black asphalt shingle.

Lance Knobel

Lance Knobel (co-founder) has been a journalist for nearly 40 years. Much of his career was in business journalism. He was editor-in-chief of both Management Today, the leading business magazine in Britain,...

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  1. Thanks Bruce, as I learned from that page, the global warming reduction from a cool roof is as much about the reduced energy input to drive air conditioning as it is about the reduced load on air conditioning equipment.  So, if you don’t have A/C, your energy input for that is already zero and you’re not generating greenhouse gases that a cool roof could reduce.  

    A cheap alternative, which I installed in my home, is staple-up radiant foil, under the roof rafters.  That bounces radiant heat back up through the roof.  It has lowered my attic temperature significantly on warm days.  And it’s reflective on the underside too, so wintertime heat loss through the roof is reduced.  If I had A/C the equation would be different, but in Berkeley, I don’t know anyone who bothers.  I guess Advanced Light Source must have it.

  2. How much of the energy gain from a cool roof is based on the assumption that the interior is air conditioned?  I realize the point is being made on a national scale, where that’s certainly relevant, but in Berkeley housing stock, does a cool roof still make sense?  Does a reflective roof mean that you lose solar heat gain during the winter and so increase the cost of heating?  Maybe that doesn’t matter as most attics aren’t conditioned space.  Would be curious to hear from someone who knows this topic better than I.