Imagine if every house had a green roof, instead of traditional shingles or roof tiles? This is the community of Wohldorf-Ohlstedt near Hamburg, Germany. This was the first stop on our day of excursions to various green roofs in the Hamburg area for the 3rd International Green Roof Congress. It was also the most impressive (a) because of the beauty of the very natural looking roofs covered in grasses, and (b) because these roofs were constructed in the 1940's and seem to still be functioning quite well. In fact, the town council has mandated that any renovation projects or new constructions within the original area of the neighborhood must have or maintain a green roof.
In these satellite images below, you can see the juxtaposition of the traditional roofs of the neighboring houses and the greenery in which you can just make out the roof borders.
There is not much actually known about the construction and maintenance of these private homes, it seems. We were told on our tour that they were constructed in 1943/44 as one of three "Norwegian settlements". The neighborhood was intended to be a social housing option for the needy, including former concentration camp prisoners, but has since developed into a medium class suburb with the green roofed houses becoming quite sought after and rarely available.
On a couple of roofs, we could see a very basic build-up showing a bituminous layer for root and water protection. The plants are mostly grasses with some wildflowers and other local plants that have popped up over the years. The biggest challenge is the birch forest surrounded the properties, making it necessary to check the roofs twice a year or so for tree seedlings. There wasn't any information on leaks or any other maintenance, but a lot of the roofs looked like they were doing fine without much attention. They don't seem to be irrigated (but perhaps in summer). The newer roofs have employed the more standard sedum systems from companies like ZinCo (our congress sponsor), but the older ones have a more bio-diverse and spontaneous plant selection predating the development of green roof system packages.
It was an encouraging project for those of us interested in small-scale residential green roofs, showing that under the right conditions it may not be necessary to over-engineer plant selection to a point of installing only sedums. These houses also serve as excellent examples to show clients of how beautiful a green roof can be - they change with the seasons, bring wildlife to an otherwise unused area, and contribute to additional permeable ground cover for storm-water runoff and heat mitigation.
I'd be very interested in knowing more about the history and maintenance of these houses. If you have any more information or edits to my observations, please leave a comment below!