Phila. contest aims to whiten city's roofs

Posted on Thu, Feb. 18, 2010
By Sandy Bauers
Inquirer Staff Writer

After the recent bad weather, Mayor Nutter knew that getting people excited about putting white stuff on their roofs might be a tough sell.
"But this is a different kind of material," he said with a brief laugh yesterday.

He was talking not about snow, but about reflective coatings - the kind that could turn Philadelphia's rooftops from a sea of searing black to an ocean of cool white.

Nutter was launching a citywide block contest to promote the coatings, which not only can make a house cooler but also, according to the latest research, potentially can make entire neighborhoods and cities cooler.

Each house on the street that wins the "Coolest Block" contest will get a white roof, plus insulation, air sealing and an energy audit, estimated to be worth from $3,000 to $3,500 per home.

The improvements could lower monthly energy bills by 20 to 30 percent.

The idea of a white roof's cooling a building - like that of a white shirt's cooling a person - is hardly new, although the technology has progressed far beyond mere white paint to materials with even greater reflectivity.

"Cool roofing has been the hottest trend in commercial roofing," said Jerome Peribere, president and chief executive officer of Dow Advanced Materials, which is donating materials.

Last year, white roofs got a boost from Energy Secretary Steven Chu, who said they might slow global warming.

Months later, President Obama publicly announced that insulation was, of all things, "sexy."

"For way too long, we have talked about energy efficiency," said Gil Sperling, a senior adviser for the U.S. Department of Energy. "Now, we actually are starting to do something about it."

He said Philadelphia's contest was the first of its kind in the nation.

Blocks of rowhouses make up 75 percent of the city's housing. On a hot day, the temperature on those flat black roofs can top 190 degrees, which radiates through the structure, said Liz Robinson, executive director of the Energy Coordinating Agency of Philadelphia, a nonprofit partner in the "Coolest Block" program.

She called the average rowhouse "a brick box with a black heat collector" - excellent at retaining heat, "lousy at shedding it."

White roofs can be from 50 to 80 degrees cooler.

The coating that will be used for the winning block is an acrylic elastomer that dries to a flexible skin, able to accommodate a roof's normal expansions and contractions. According to the energy agency, the coating could extend the life of a typical asphalt roof by 10 years.

Robinson first began thinking about white roofs in the summer of 1993, when 118 Philadelphians died during a weeklong July heat wave.

Her organization distributed about 5,000 air conditioners. But she knew that most of their recipients could hardly afford higher energy bills. She also worried that overloaded wiring in older homes might pose a fire hazard.

"It felt really schizophrenic," Robinson said.

The agency has since received enough funds to put white roofs on 600 homes. Independent evaluators concluded that temperatures upstairs in them were as much as five degrees cooler on hot days.

None of this surprises Hashem Akbari, a scientist who for three decades has studied the "urban heat island effect."

He and others at the Lawrence Berkeley National Laboratory in California have shown that because of dark roofs and pavements, many urban areas are from six to eight degrees warmer than surrounding rural areas.

They estimated that white roofs could save Philadelphians $3 million a year in energy costs. In winter, the white roofs would not affect heating costs appreciably, he said.

Now a professor and leader of the Heat Island Group at Concordia University in Montreal, he is trying to organize the 100 largest cities in the world to develop programs to whiten their roofs.

Using new computer models to simulate the solar radiation absorbed - or reflected - by cities, scientists at the National Center for Atmospheric Research in Boulder, Colo., recently concluded that if every urban roof were painted white, the world's cities would be an average 0.7 of a degree cooler on a summer day.

New York - similar to Philadelphia - would be two degrees cooler.

Actually re-coating all those roofs is improbable, conceded coauthor Gordon Bonan, but "the take-home point is that the idea of white roofs is technically sound and can have a cooling effect."

Philadelphia's Greenworks sustainability plan has set a goal of retrofitting 15 percent of the city's homes with reflective roofs.

Councilman Jim Kenney also has proposed a bill requiring cool roofs on all new commercial construction and roof replacements - as California has required since 2005 - and said he would support a tax incentive for residential white roofs.

"It first started out that this is what's good for the environment, and we're all hugging trees," he said yesterday. "But this saves money."

http://www.philly.com/inquirer/local/pa/20100218_Phila__contest_aims_to_...