Rooftop Dunes Bring the Beach to the City

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Groenmarkt dune roof / Buro Harro

The beach is 15 miles from the center of Amsterdam, but a small piece of it will soon exist among the windy rooftops of the city. Buro Harro, a Dutch firm co-led by landscape architect Harro de Jong, in conjunction with Ronald Janssen Architecten and Bastiaan Jongerius Architecten, are building a dune roof on one building of the Groenmarkt complex. The team won the competition for the project in 2015 and construction is scheduled to be completed in 2020.

Groenmarkt (Green Market) was a fruit and vegetable market that occupied the block from 1898 to 1934. Today, the complex consists of a 35-unit apartment building, four private town homes, and a small urban square linking the buildings. The complex sits along the Singelgracht, a canal that once marked the outer limit of the city.

The design team transformed the notion of the green roof. Much of the development in Amsterdam is similar in height, approximately 14 meters (45 feet), which de Jong describes as a place where “the wind blows as in completely open landscapes.” The unique rooftop micro-climate inspired the team to draw from a similar windswept landscape that Dutch people enjoy, even during stormy weather: the beach.

The roof will be complete with sand, beach grass, and a salt water pool. De Jong believes “the sounds of Amsterdam in the background will be like the murmuring of the sea.”

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Saltwater pool situated within the dunes / Buro Harro

Accomplishing this feat is not as simple as it sounds. Beach ecosystems are fragile, with each layer of dunes playing a vital role. Dunes rely on colonizing species, usually grasses to help secure the top layer of sand from blowing away. Eventually layers of dunes develop, from primary, closest to the water’s edge, to tertiary. Tertiary dunes are more stable, because of decreased wind exposure, which allows more plant growth and even some small trees to grow within them. Buro Harro plans to use this kind of dune for the Groenmarkt roof.

In order to do this, the firm will transplant part of the dune onto the roof. They used this technique for Bartokpark, but now face the added difficulty of trying to move a dune on to the roof.

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Transplanted dune in Bartokpark / Buro Harro

Ultimately, the effect will be a fully-formed tertiary-like dune, with a variety of grasses and a few small trees to provide shade and further stability. The transplantation method provides an ecological base to work from, but the team will consult with ecologists to ensure the dunes are able to thrive.

Typical dune fencing will establish the boundary of the walking space on the roof, with walking paths keeping people off the grasses.

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Beach fencing seen from the pavilion / Buro Harro

Other elements of the project: trees will be introduced in the plaza, encouraging residents to use the plaza throughout the year.

Typically, residential blocks in Amsterdam are formal and flat on their public facade, while the interior courtyard is a collage of balconies and greenery.

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Typical block in Amsterdam / Photo by Liene Ratniece on Pexels.com

The team decided to invert this relationship so that, according to de Jong, “the outside of the building becomes very irregular and very green.”

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View of Groenmarkt from the Singelgracht / Buro Harro

The decision to turn the social space outward gives the project an identity from the river and improves connectivity with the plaza. De Jong also created pre-fabricated nesting spaces in the facade for bats and birds. Holes in the floor slabs allow vine growth.

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Vine structures spanning multiple floors / Buro Harro

Buro Harro has plans for other kinds of roof environment — for instance, orchards or wet landscapes that contain stornwater runoff. De Jong has found people will pay extra for integrated architecture and landscape. This allows his firm to “multiply landscapes through architecture,” creating spaces for both people and biodiversity.

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