Some green & gritty rooftops in Basel, Switzerland

In September I visited Dusty Gedge, toured some green roofs in London, and learned about the latest in U.K. designs that promote biodiversity. December 8 thru 11, I visited Stephan Brenneisen in Basel Switzerland and Wolfgang Ansel in Stuttgart Germany.

Basel and Stuttgart are two of the green roof hotbeds on the European continent. To put this into perspective here's some estimated green roof areas in Basel, Stuttgart, Dusseldorf (another green roof rich city), London, Portland, and Chicago:

Basel, Switzerland: ~700,000 m² in 2007 (estimated by Stephan Brenneisen).
Dusseldorf, Germany: 730,000 m² in 2008 (according to a detailed inventory)
Stuttegart, Germany: >1,000,000 in 2009 (entire metro-area estimated by Wolfgang Ansel)
London, England: 500,000 m² (estimated by Dusty Gedge)
Portland Oregon: 62,000 m² in 2009 (according to Amy Chomowicz)
Chicago, Illinois: 49655 m² in 2008 (according to Green Roofs for Healthy Cities)

Basel is purported to have the highest per-capita area of green roof in the world. This is in part because the city has had local regulations for over a decade that require all new development to incorporate green roofs where technically feasible.

Stephan Brenneisen on the new Stucki Shopping Center Greenroof

But quantity should not be the only measure in green roof progressiveness. That was abundantly clear from my visit with Stephan Brenneisen in Basel Switzerland. Stephan is head of the Green Roof Centre of Competence at the Zurich University of Applied Sciences Wädenswil where he conducts research and advises on green roof policies and designs. Stephan did his PhD studies on how different green roof substrate depths influence biodiversity and continues to actively promote the design of green roofs for biodiversity. For a sample of his writing in English see this recent paper in Urban Habitats: Space for Urban Wildlife: Designing Green Roofs as Habitats in Switzerland."

Stephan's efforts are clearly a factor in Basel's leadership in green roofs. He is actively involved in developing and refining green roof policies in Basel and was instrumental in helping develop and adopt new, cutting-edge mandates that require all green roofs to incorporate design features which promote biodiversity.

Stephan took me to three green roofs in the Basel-area and gave me the information for a self-guided tour of three additional sites. December is probably the worst season of the year too tour green roofs but I have found some spring and summer photos of the sites I visited to better capture some of Basel's rooftop beauty. Many of the biodiversity-friendly roofs that Stephan shared had design features I encountered in London- varied substrates and topography to promote habitat diversity- but there were some interesting differences too.

Stucki Shopping Center Green Roof

One example of this is the relatively new Stucki Shopping Center Greenroof just installed in September (2009). The Stucki Shopping Center roof is 35,000 m² (roughly half the size of all the greenroofs in Portland) and is covered by mix of substrates ranging up to 12 cm in depth.

Stephan has been promoting green roof designs that use local or native soils from disturbed greenfield development sites. At the Stucki Shopping Center, the substrates include cobble, gravel, silt-clay soils, and some organic material some of which was gleaned from surface soils at a local mining site. As you can see, the roof is only four months old but already has substantial plant growth, atleast where the substrate is deeper.

Stephen on the Stucki Shopping Center roof.

Varied substrates and different depths and vegetation growth on the Stucki Shopping Center roof.

December bloom on the Stucki Shopping Center roof.

Beds on the roof perimeter provided rooting soil for green wall vegetation on the building exterior.


Stucki Shopping Cennter from the air (Photo from Architectural Review).

Perhaps because of the longer history of green roof installation in Switzerland, a number of Stephan's projects have involved ecological enhancement of existing green roofs originally designed for other purposes. Stephan has been involved in several projects that installed new substrates, varied topography, and/or organic material (from grass cuttings to woody debris) into existing green roofs in order to better promote biodiversity values.

Basel Main Exhibition Hall (Messehalle Basel) Green Roof

One spectacular example of this is the 8,000 m² Basel Main Exhibition Hall Green Roof. The roof was originally installed in 2000 with 7cm of volcanic substrate and planted with sedums.

The Basel Main Exhibition Hall Green Roof is purportedly the largest greenroof in Switzerland. I think this photo predates the biodiversity enhancements co-designed by Stephan.

In 2008 Stephan worked with local artists and the Exhibition Hall owners to add organic matter and woody debris to a roof to enhance biodiversity functions.

The early winter photographs I took don't do really this green roof justice, so here's some spring or summer photos I snagged from the greenroofs.com website:

The Exhibition Hall green roof includes PVCs that produce 215000 kwh/year and whose efficiency is improved by the cooling effect of roof vegetation.

Cantonal Hospital Greenroof

The 3000 m² Cantonal Hospital Greenroof was installed over 30 years ago as an aesthetic enhancement for hospital patients in recovery. In 2003 Stephen helped redesign the roof for a biodiversity. The soil is sand loam and gravel ranging from 8 to 25 cm deep, intended to stimulate river terrace and dry meadow habitats.

Varied substrate depth and vegetation.


The Cantonal Hospital green roof is visable from the patients' rooms.

I spent the afternoon walking in and around Basel visiting some other accessible green roofs that Stephan recommended I see. Below are some photos I took along the way.

Okay this roof looks like an airduct coming out of a vacant lot but it is actually atop the Restaurant Rypark next to the Rhine River where it mimics river terrace habitat.

I encountered this rural green roof atop barn just outside of the suburb of Pratteln.

Here's a volunteer green roof. Who says green roofs are high maintenance?

I had a delightful and engaging visit with Stephan. Apart from all the green roofs, I also had the pleasure of meeting his partner Barbara and their very adorable children (ages 6 and 8, I think) which gave me a very special window into Swiss home life during the Christmas season.

For a great short video of Stephan and Basel's green roofs see Amy Wong's World Radio Switzerland report, Green: Basel's green roof initiative.

Next stop: Greenroofs of Plenty in Stuttgart, Germany.

Earlier post:


London's Dusty Gedge and Ecoroofs for Biodiversity