A green roof in Cambridge seen in 2008. Cambridge City Hall’s pointed tower is at center right in the distance. (Photo: Mike Linksvayer via Flickr)

Requirements for “vegetated roofs” – also known as green roofs – on new or substantially renovated mid-rise, high-rise and commercial buildings were proposed Thursday in Somerville’s Land Use Committee by Ward 3 city councilor Ben Ewen-Campen and at-large councilor Jake Wilson.

Per the proposal, 80 percent of available room space – that is, space not dedicated to mechanical equipment, solar panels or other required equipment – would need to be covered in vegetation. The councilors encouraged passage of the amendment for its potential to mitigate the effects of climate change.

“We’re sitting here on a 90-degree day in September, so it should be pretty obvious to everyone why this is important,” Wilson said.

Cambridge has a similar law for buildings of more than 25,000 square feet, approximately the same square footage as Somerville’s mid-rise buildings, Ewen-Campen noted.

The amendment does not include specific requirements such as soil depth and types of plants; keeping the language vague avoids running into issues because the building code is regulated at the state level, Ewen-Campen said. Still, he added, aspects such as green scores – another part of Somerville’s zoning code that rates buildings based on green space – could incentivize developers to build more intentionally.

“Somerville has already lost the vast majority of its natural spaces,” said Renee Scott, an advocate with Green & Open Somerville and a citizen sponsor of the new zoning. “We need to get creative about bringing nature back to our lives.”

Brendan Shea, another community advocate, examined Assembly Square and Cambridge’s Kendall Square to see how much green roof space could be dedicated around mechanical structures. There’s significant available space for greenery in Somerville when compared with Cambridge, Shea said.

According to the federal Environmental Protection Agency, patches of nature are cooler due to providing shade and releasing moisture through evapotranspiration, while cities’ lack of green spaces creates urban “heat islands.” The green roofs could help reduce the heat, city officials and public commenters said. Tori Antonino said the roofs could even provide habitats for native animals.

One commenter expressed worry that exemptions to the amendment allowing solar panels and for cellular and radio towers would encourage developers to rent out more of their roof space. In response, Ward 5 councilor Beatriz Gomez Mouakad asked for further study and clarification on whether having green roofs without allowing space for solar panels would prevent the city from reaching its renewable energy goals. Mouakad also questioned whether green scores would effectively encourage developers to incorporate green roofs.

Officials will revisit the proposal after public comment closes on Friday.