Green roofs — using grass or other plants instead of shingles — have long been known to cut a building’s heating and cooling costs and reduce polluted stormwater runoff, but they could also provide an eco-friendly way of sequestering substantial amounts of carbon, according to a new study.

For example, covering all the rooftops in the Detroit metropolitan area with greenery would help store 55,252 tonnes of carbon dioxide within the plants and underlying soil. That’s the equivalent of taking some 10,000 mid-sized SUVs or trucks off the roads for an entire year.

“Although green roofs are often adopted for energy savings and heat island mitigation, rarely has this technology been promoted for its ability to mitigate climate change,” write the researchers from Michigan State University. “While (the carbon storage benefits) depend on climate and green roof design, they nonetheless represent a small but significant potential for sequestering carbon in urban environments.”

The research team studied carbon intake at eight green roofs in Michigan and four roofs in Maryland that ranged in age from one to six years. They also assessed another 20-plot roof in Michigan to determine the impact of different soil choices on carbon sequestration.

The researchers measured the total amount of carbon stored at each location by harvesting both the above-ground greenery as well as the underlying substrate and biomass, drying all the material then analysing its carbon content.

“Roofs are typically unused spaces; therefore, they provide a unique opportunity to sequester carbon,” they write in their research.

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