A White Roof Is a Cool Roof

SUBHEAD: Save energy and money by switching to a white, or “cool,” roof, for about the same cost as a conventional roof. Image above: Greek island stucco homes have been whitewashed for centuries. Note the old windmill on the hill. From http://www.thedailybanter.com/tdb/2009/05/paint-your-roof-white-to-save-the-planet.html By Amanda Kimble-Evans on 10 November 2009 in Mother Earth - http://www.motherearthnews.com/Green-Homes/Cool-Roof-White-Roof.aspx Most of us know better than to wear black on a hot day, but when it comes to the roofs on our houses, the aesthetics of black take priority. That is, until temperatures rise and we find ourselves cranking the air conditioner, with our electric bills following suit. The good news is you can save money by lightening the color (and therefore the temperature) of your roof, or switch to a white roof the next time your house needs a new hat. Also, white roofs, aka cool roofs, are a “hot” topic these days as a means to help stem global warming. The Benefits of a White Roof

Switching to a white roof can actually reduce energy use by about 20 percent in hot, sunny weather, according to the Lawrence Berkeley National Laboratory Heat Island Group. According to Heat Island Group lead scientist Hashem Akbari, transitioning to reflective roofing (and pavements) in the world’s urban areas would offset the equivalent of emissions from the planet’s 600 million cars for the next 18 years. In addition, a 1,000-square-foot white roof saves air conditioning use that otherwise would emit about half a ton of carbon dioxide per year. (The average total square footage of a home in the United States is more than 2,000 square feet.) Over the 20-year life of the roof, that stacks up to 10 tons less carbon dioxide emissions.

When the Heat Island Group recorded data on a commercial building in Davis, Calif., they found that installing a white roof caused an 18 percent drop in their average electricity use for air conditioning. In urban areas, white roofs help lower locally increased temperatures due to the large proportion of paved surfaces, which results in reduced smog levels. The list of benefits for white roofs goes on and on.

“This will not be the silver bullet that solves the global warming problem, but it cools your home, helps cool the globe and puts money in your pocket,” Akbari says.

Critics have suggested white roofs do more harm than good in northern climates. But research shows that the heating benefits of a dark roof in the winter are negligible because days are shorter, skies are cloudier, the angle of the sun is low and sometimes roofs are covered in snow. And there isn’t much negative impact with a white roof in areas where air conditioning is in use at least part of the year.

“The amount of heat savings you may lose in the winter would be, at the maximum, 30 percent of the summertime savings a white roof would provide,” Akbari says. “If you have a building that needs cooling in the summer and heating in the winter, no matter where you are, having a white roof will save you money.”

Cool Roof Options

“Cool” is the buzzword that encompasses a range of roofing materials that can reduce carbon footprints. And cool roof products come in a surprising rainbow of colors.

“White can scare people a little bit, especially homeowners or homeowners associations,” says Michelle van Tijen of the Cool Roofs Rating Council. “As more people are educated about the range of cool roofing systems available, our hope is that big areas of residential homes will transition.”

A cool roof is measured by two properties: solar reflectance (the ability of the product to reflect energy away from the roof) and thermal emittance (the ability of the roof to radiate absorbed heat). Ideally, you want your roof to have both a high solar reflectance and a high thermal emittance.

The best time to install a cool roof is when a new roof is needed or major roof maintenance is in order. “In those conditions, the difference in energy savings between “cool” asphalt shingles, “cool” tile or “cool” painted metal is sufficient to justify any incremental cost difference in installation,” Akbari says. And, according to the researchers, there’s little to no difference in the costs of different roof colors (as opposed to roof materials), so payback from your cool roof would be immediate.

Reflective Roof Coatings

Not ready for a new roof but still want to cool down? Install a white roof coating instead. There are a number of coatings to consider, such as liquid rubber, liquid polymer or elastomeric sheeting, that will substantially improve an existing roof’s reflectance/emittance. Many of the coatings can be applied on asphalt shingles, too. Plus, coatings protect and seal, potentially extending the life of your existing roof. The cost of coating an existing roof is about $0.50 to $1 per square foot, according to Akbari, so it will be paid back by the energy savings and extended life of your roof.

Find the Best Cool Roof Materials

The Heat Island Group has developed a Solar Reflectance Index (SRI) that provides a single score for cool roofs. Although not widely used yet, you can browse the Lawrence Berkeley National Laboratory’s Cool Roofing Materials Database, or ask local roofing specialists whether an SRI score is available for a product you are considering. The Heat Island Group says shingles rated at SRI 30 percent or higher will keep a home cooler and reduce energy bills.

The Cool Roof Rating Council also offers a product directory that lists roofing options and their scores. And if you’re looking to take advantage of the federal tax credits for installing an energy efficient roof, it must be rated through the Energy Star program and it has to be a new roof. You can find lists of state-by-state rebate programs online at the Database of State Incentives for Renewables & Efficiency, but van Tijen recommends that you call your local utility company to see if they have additional programs.

[Rain and Stormwater Harvesting Note]

The potability of the harvested rainwater is dependent on many factors. The most obvious is the material of the catchment surface, or, in this case, the roof. The smoother the catchment surface, the better. Metal roofing materials, whether galvanized corrugated steel or aluminum, provide a smooth, bacteria un-friendly surface for rainwater to flow down. There are many options of various styles, alloys, and colors of metal roofing. Care should be taken on all re-roofing to not use lead flashings, as these will contaminate the water supply.

1 comment :

Jill said...

Thanks for a good story on white roofs, an age-old, common sense practice that is being rediscovered by our modern "smart" society.

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