Green roofs can help cool cities in the summer heat, but building them is only the first step. Many don't survive

As summer temperatures in the United States and Europe continue to reach record highs, cities are grappling with the dangerous heat they are experiencing. Traditional cooling methods, such as air conditioning, are straining power grids and creating uninhabitable conditions in some apartment buildings. Green roofs, which are living rooftops covered in plants, offer a promising solution.

By transforming heat-absorbing rooftops into cooling solutions, green roofs can help mitigate the urban heat island effect and make cities more resilient to extreme weather. However, simply installing a green roof is not enough to ensure its long-term success. Research shows that many green roofs are neglected and fail to survive beyond a few years, often due to maintenance costs.

When building operational budgets are reduced, maintenance for landscape elements like green roofs may be scaled back or eliminated altogether. Unlike conventional roofs, green roofs consist of multiple layers, including insulation, waterproofing, and drainage, which allow plants to thrive. These roofs can support a variety of vegetation, from low-growing sedums to shrubs and trees.

Not only do they provide aesthetic benefits, but they also absorb sunlight, cool the surrounding air through evapotranspiration, reduce heating and cooling energy needs, and help manage stormwater runoff. Incentives offered by organizations like the European Commission and the U.S. Environmental Protection Agency have encouraged the adoption of green roofs, with cities like Philadelphia offering tax credits to businesses that install them.

Despite the numerous benefits, many green roofs fail to deliver on their promise. Our study of 46 green roofs across the southeastern United States revealed that nearly half were no longer functioning as intended. Some had been abandoned with vegetation loss and no maintenance, while others were completely removed. The success of a green roof depends not only on its design but also on the stability of building ownership.

Every time ownership changes hands, there is a risk that the green roof will be abandoned or removed. The maintenance costs associated with green roofs can vary from a few cents to over $3 per square foot per year, and require ongoing monitoring, watering, fertilizing, and pest control. Without proper care, the environmental benefits of green roofs can quickly diminish.

Investing in green roofs is more than just a one-time construction project; it requires a long-term maintenance plan and clear ownership to ensure their continued success in combating urban heat.