Roofing Costs - Cost of Roofing - Roofing Cost

    

Cool Roofs

Dark materials absorb more heat from the sun--as anyone who has worn a black t-shirt on a sunny day knows. Black surfaces in the sun can become up to 70°F (40°C) hotter than the most reflective white surfaces. If those dark surfaces are roofs, some of the heat collected by the roof is transferred inside.

Potential net energy savings from changing roof reflectivity. Savings are measured in dollars. Note that the net savings are the savings of cooling energy use less the penalties of heating energy use.

Staying comfortable in under a dark shingle roof often means more air conditioning and higher utility bills. These roofs also heat the air around them, contributing to the heat island effect. Conversely, cool roofs can reduce the heat island effect and save energy. In a study funded by the U.S. EPA, the Heat Island Group carried out a detailed analysis of energy-saving potentials of light-colored roofs in 11 U.S. metropolitan areas. About ten residential and commercial building prototypes in each area were simulated. We considered both the savings in cooling and penalties in heating. We estimated saving potentials of about $175 million per year for the 11 cities. Extrapolated national energy savings were about $750 million per year.

The Heat Island Group has monitored buildings in Sacramento with lightly colored, more reflective roofs. We found that these buildings used up to 40% less energy for cooling than buildings with darker roofs. The Florida Solar Energy Center performed a similar study, also showing up to 40% cooling energy savings.

The Heat Island Group continues to monitor buildings and measure or simulate the effects of increased roof reflectivities for:

• different types of buildings,
• different climate zones and seasons, and
• different roof insulation levels, angles and orientations.

This important research is needed to find the best ways to save energy and money using reflective roofing.

Solar reflectivity is measured according to ASTM E903. Traditional roofing materials have an SRI of between 5% (brown shingles) and 20% (green shingles). White shingles with SRI's around 35% were popular in the 1960s, but they lost favor because they get dirty easily. The current trend is to make white shingles more reflective.