Permeable Pavers: Antidote to Urban Heat Effect?

New findings demonstrate that porous and permeable pavements are well suited to reduce urban heat island effect, especially under wet conditions. Designers installing these pavements might be eligible for 3-4 LEED points for the stormwater management and heat mitigation benefits of permeable surfacing.

Permeable pavers, a growing niche in the green infrastructure market, are popular for their ability to filter stormwater runoff. New research is documenting another environmental benefit – relieving urban heat island effect.

Conventional surfaces typically reflect only about five percent of the sun's energy, absorbing the rest as heat. Since more than a third of most cities are covered by pavement – usually impermeable concrete or asphalt – urban air on a sunny afternoon can be 2 – 5 degrees Fahrenheit warmer than rural air nearby. Elevated air temperatures, known as the "urban heat island" effect, strain the power grid by making air conditioners work harder to cool buildings, and can degrade air quality by accelerating smog formation.

"Reflective and permeable pavements are the most promising practices to address the built-environment issues related to heat-island mitigation, and permeable pavements are a promising strategy for stormwater runoff management," Hui Li of the University of California, Davis, told environmentalresearchweb. "This innovative approach will potentially solve both problems, especially in urban areas."

Li and his colleagues tested the level of reflected light, or albedo, of six permeable and three non-permeable sections of pavement, using four-meter-square areas. The non-permeable asphalt reached temperatures nearing 160 ???(R)???AE?F, with an albedo of 0.08 – 0.09. The permeable sections were 20 – 50 ???(R)???AE?F cooler than the concrete pavements, and had albedos of 0.18 – 0.29. Under wet conditions, the cooling effect of the permeable pavements on the surface and near-surface air temperatures was even more apparent compared to the impermeable surfaces.

"Our research study extends the pavement-cooling effect to evaporative cooling and thermal resistance. It was found that to be effective for evaporative cooling, water must be near the surface in a permeable pavement," said Li. "Most cool-pavement studies focus only on the reflective cooling from increasing the albedo."

Li and his team published their study in Environmental Research Letters (ERL) as part of the ERL Focus on Environmental Assessments in the Built Environment. The report also discusses strength testing on permeable pavements for the ability to carry heavy-duty loads while retaining permeable properties.