Bengaluru study finds green roofs can lower temperatures by up to 5°C

Green roofs cool Bengaluru by 5°C, finds IISc study

A new study from the Indian Institute of Science (IISc) has put hard numbers behind an idea that urban planners have long floated. Researchers found that buildings with green roofs — rooftops covered in grass, shrubs or small plants — can bring down the surrounding air temperature by as much as 5 degrees Celsius compared to conventional concrete or tile roofs.

The findings come at a time when Bengaluru, like many Indian cities, is grappling with rising urban heat. The city has lost significant green cover over the past decade to construction, leading to what experts call an urban heat island effect.

How the study was done

IISc scientists monitored temperature readings on several buildings across the city over an 18-month period. They compared structures with green roofs against those with bare, exposed roofing materials. Sensors recorded ambient temperature, humidity, and surface heat at regular intervals.

The results were clear. Green roofs not only stayed cooler themselves — surface temperatures were up to 15°C lower — but also cooled the air immediately around them. The cooling effect was most pronounced during peak afternoon hours, between 1 pm and 4 pm.

Additional benefits observed

Beyond temperature reduction, the study noted other advantages. Buildings with green roofs consumed 15 to 20 percent less energy for air conditioning. The vegetation also helped retain rainwater, reducing runoff during monsoon months.

The researchers said the plants used were native species requiring minimal irrigation. This makes the solution practical for Bengaluru, which faces water scarcity even as it battles heat.

Urban planners take note

The Bruhat Bengaluru Mahanagara Palike (BBMP) has expressed interest in the findings. Officials said they are exploring policy incentives for new buildings to include green roofs. Some residential colonies in south Bengaluru have already experimented with terrace gardens, but this study gives them data to back up the practice.

Architects and real estate developers who attended a recent IISc seminar on the study said the cost of installing a green roof — roughly Rs 300 to Rs 500 per square foot — can be recovered within five to seven years through energy savings alone.

Challenges remain

Not everyone is convinced. Critics point out that retrofitting existing buildings with green roofs requires structural checks. Not all rooftops can handle the extra weight of soil and water. Maintenance, too, is a concern — dry spells or pest infestations could undo the benefits.

The IISc team acknowledged these issues but stressed that for new constructions, the additional load can be factored into the design from the start. They recommended that the BBMP mandate green roofs for all large commercial and residential projects above a certain size.

What comes next: The BBMP is expected to release a draft policy on urban greening within three months. The IISc study will likely form the technical backbone of that proposal. For Bengaluru, the question is no longer whether green roofs work — it is how fast the city can scale them up.