In a move that is certain to change the color paradigm for roofing shingles, last week U.S. Department of Energy (DOE) Secretary Steven Chu directed his agency to implement cool roof technologies in all new buildings, roof replacements and roofing retrofits whose energy savings justify the cost of replacement.

Because these cool roof technologies rely primarily on the use of white or lighter-colored shingles or substances, and/or special coatings that reflect more of the sun’s heat, the roofing industry as a whole is likely ramping up its color spectrum to reflect the change.

Which brings to mind an interesting question. Why are most modern roofs dark in the first place?

The common argument is that white gets dirty fast, and looks old. This is only partly true. The second – that typical pigments (like titanium dioxide) used in composition shingle particles, paint for metal roofs, and pigment in clay tiles, are toxic – is also only partly true.

In fact, the tradition of dark roofs isn’t really very traditional. Up until the 1950s, many roofs in the U.S. were white or pale, as was siding, due to the fact that air conditioning didn’t become popular and affordable until later in the decade.

Even today, most roofs in tropical climates remain either pale or white. This includes clay tile, shingle or composite, and metal roofs.

In Bermuda, so many of the roofs are white that the effect is blinding when viewed from the bay. The same is true in Puerto Rico, where a massive apartment complex above the beach looks like a modern Anasazi cliff dwelling. Even in Florida, the number of white or pale roofs exceeds the norm.

Chu’s announcement is an extension of President Obama’s Executive Order on Sustainability, which has the government reducing its greenhouse gas (GHG) emissions by 28 percent by 2020.

According to Chu, the government – the largest consumer of energy in the country – is tackling global warming, or climate change, from the standpoint of energy efficiency, which is one of the cheapest yet most effective ways to reduce the GHG emissions like carbon dioxide (CO2) that are contributing to warming.

The mandate sets the target for new or replacement roofs at R-30, with a minimum three-year aged Solar Reflectance Index (or SRI, a measure of the roof's ability to reject solar heat). These standards are set by the Cool Roof Rating Council, or the American Society for Testing and Materials (ASTM)

According to the Lawrence Berkeley National Laboratory, or LBNL, over 60 percent of the horizontal surfaces in the nation are roofs or pavements. This leads to what experts call the "heat island effect", as dark surfaces absorb and hold the sun’s heat to create extreme urban temperatures which lead to illness and fatalities. In the U.S., heat is the number one killer.

By installing cool roofs to reduce this heat island effect, Chu hopes to reduce energy use, whose production in the U.S. comes largely from coal.

Coal-fired power plants, notes the Union of Concerned Scientists, produce more than 80 percent (or four out of every five tons) of the carbon dioxide emitted by all sources of electricity generation in the nation.