April’s #TheGlobalGrid Twitter chat was dedicated to green roofs, a special sustainable building feature gaining popularity in cities around the world. During our chat, we asked if green roofs benefit more than the buildings they sit atop and if their many benefits extend to the city level; contributing to citywide sustainability goals.

We are pleased to have been joined by Greenroofs.com to co-host this special World Landscape Architecture Month chat, and by four green roofs experts in Europe and the United States who constituted the chat panel:

• Tessa Duste, co-founder of Moss Amsterdam,
• Ben Flanner, Director of Agriculture, President, and co-founder of Brooklyn Grange Rooftop Farm in New York City,
• Dusty Gedge, co-founder of Livingroofs.org and the current President of the European Federation of Green Roof Associations (EFB) in London,
• Linda Velazquez, ASLA, LEED, AP, GRP, publisher, and editor of Greenroofs.com.

The conversation was structured around five questions. Our panelists’ answers were perceptive and insightful. Check a summary of their contributions below:

1. Green roof design and type depend greatly on the structure of their host building

Green roofs present an extra load that should be accounted for in the structural calculations of new buildings or tolerated by the structures of existing buildings. While growing food might be one of the most popular features of green roofs, most existing buildings structures are not apt to carry the extra weight of intensive green roofs. Retrofitting projects can, therefore, be often limited to installing extensive green roofs which still have great environmental benefits.

Q1A1 #TheGlobalGrid Bottom line is you need a structural engineer to determine weights, and then you design backwards from there. What does the client want, how will the #greenroofs perform - biodiversity, urban ag, etc?

— Greenroofs.com (@greenroofs) April 18, 2018

2. Green roof costs are offset by their long-term benefits at the building and community scale

Green roofs are long-term investments. At the building level, they extend the roof’s life, reduce its energy costs and increase the property’s overall value. The benefits for the community are even greater. Green roofs contribute to making communities more sustainable and climate resilient. Accessible green roofs create additional open spaces for community activities and increase a neighborhood’s brand value, which attracts more development and investment creating a virtuous cycle of benefits.

There is often a focus on 'productive' space but green roofs may not be productive in the traditional sense but provide a multitude of benefits to both the building neighbourhood and city that dont figure well in current ROI process - #TheGlobalGrid #greenroofs

— dusty gedge (@greenroofsuk) April 18, 2018

3. As a staple of green building, green roofs ought to be mandated in city building codes

While it is easier for cities to make green roofs a requirement for new buildings, the incentives for existing properties to green their roofs are still being experimented. Linz, Austria; Stuttgart, Germany; and Toronto, Canada are among a growing number of cities mandating the installation of green roofs on their buildings. Tax credits, rebates, along with grant programs and direct subsidies are among the tools used by governments both at the local and national levels to encourage property owners and developers to install more green roofs.

A3: #TheGlobalGrid Stuttgart example: Mandating green was a vital component, but the city identified the importance for building owners and developers to value their #greenroof as an asset rather than a requirement @green_roof_girl #research

— Tessa Florence Duste (@TessaDuste) April 18, 2018

4. Green roofs are part of a city’s green infrastructure

Green roofs’ numerous environmental benefits definitely qualify them as a component of a city’s green infrastructure. But forcing developers to take on the expense might be counterproductive. In addition to providing monetary incentives, cities should lead a parallel effort to educate developers and property owners about the environmental and economic benefits of green roofs; shifting their perspective of green roofs from expenses or liabilities, to assets.    

A5 #theglobalgrid Yes, #greeninfrastructure is critical on so many levels. We can get caught up in the challenging metrics on performance, but then ask yourselves – what if these amazing roofs across the world didn’t exist??? It’s a no brainer.

— Ben Flanner (@bjflanner) April 18, 2018

Check our Twitter moment for the whole conversation and some great examples of green roofs shared by our panelists and participants, such as the Bridgepoint Active Healthcare in Toronto, Canada:

Bridgepoint Active Healthcare is a fantastic example of how green roofs can improve patient and community wellbeing #TheGlobalGrid pic.twitter.com/9Kq17ZH2r1

— GRHC (@GRHCna) April 18, 2018

Does your city have green roofs? Would you support a legislation or a zoning ordinance that mandates green roofs on all buildings? Share your thoughts with us in the comments section below.

Don’t miss next month’s #TheGlobalGrid Twitter chat on Wednesday, May 16th at 12:00 p.m. PT. May’s chat will be dedicated to bikes and biking infrastructure in cities. Do you have ideas for topics that you would like to discuss with us in future chats? Let us know. We look forward to your participation!