Most of the roofs in the world (including over 90% of the roofs in the United States) are dark-colored. In the heat of the full sun, the surface of a black roof can increase in temperature as much as 50 °C (126 °F), reaching temperatures of 70 to 90 °C (158 to 194 °F). White surfaces reflect more than half of the radiation that reaches them, while black surfaces absorb almost all.
A 1,000-square-foot (93 m2) white roof will offset 10 tons of carbon dioxide over its 20 year lifetime. The potential reduction is GHGs is very significant. If all urban, flat roofs in warm climates were whitened, the resulting 10% increase in global reflectivity would offset the warming effect of 24 Gigatonnes of greenhouse gas emissions, or equivalent to taking 300 million cars off the road for 20 years.
A 2012 study by researchers at Concordia University estimated that worldwide deployment of cool roofs and pavements in cities would generate a global cooling effect equivalent to offsetting up to 150 Gigatonnes of carbon dioxide emissions – enough to take every car in the world off the road for 50 years.
Cool roofs have a wide range of benefits including:
- Improved energy efficiency
- Reduced greenhouse gas emissions
- Reduction in urban heat island effect and smog
- Improved occupant comfort (Less heat)
- Reduced cooling energy load
- Save peak electricity demand costs if you have time-of-use metering.
- Extended roof life service life and help
- Reduce roofing waste added to landfills.
- Comply with codes and green building programs (like Title 24 Energy Efficiency Building Standards)
White or white coated roofing membranes, or white gravel are best but Cool roofs can come in many colors, even some dark colors are EnergyStar rated, but white is the most reflective.
One contested study by researchers at Stanford University suggested that although reflective roofs decrease temperatures in buildings and mitigate the urban heat island effect, they may actually increase global temperature. However, according to a 2008 case study in the Province of Almeria, Southern Spain, cool roofs reduced the ambient temperature by 1.6ºC over a period of 20 years compared to surrounding regions.