International studio ingenhoven architects designed a building with Europe's largest green facade and used it to revitalize Düsseldorf's city center through the multi-use Kö-Bogen II complex. Construction ran from 2017 to 2020, following a design first unveiled in 2014, which won first place in the project's original international competition.
What's Inside
Kö-Bogen II covers 41,370 square meters and holds a mix of uses: 24,000 square meters of retail and dining space, 6,000 square meters of offices, and 668 underground parking spaces, all woven into the building's form. Before construction, an elevated motorway ran through this site, and its removal is part of a broader shift in how the city thinks about its center: away from car-first infrastructure, and toward planning built around how people move through and use public space.
8 Kilometers of Hedge, Not 30,000 Trees
The building's defining feature is its facade - roughly 8 kilometers of hornbeam hedge, made up of more than 30,000 individual plants, covering the building's sloping green walls. These are not 30,000 trees, as the project is sometimes described, but 30,000 hedge plants, and according to ingenhoven architects' own figures, their combined ecological benefit is roughly equivalent to 80 fully grown deciduous trees - a meaningful contribution, but a different scale than "30,000 trees" implies.
Hornbeam was chosen because, as a native hardwood species, it holds onto its leaves through winter rather than dropping them, meaning the facade stays visually intact and functional year-round, shifting color with the seasons rather than disappearing. Ingenhoven worked with structural engineer Werner Sobek and Professor K.-H. Strauch of Berlin's Beuth University of Applied Sciences to develop the planting system itself - getting thousands of individual hedge plants to grow reliably on a vertical, sloped surface is a separate engineering problem from the architecture around it.
A Response to Urban Heat, Not Just a Visual Statement
Green surfaces like this one help counter a persistent problem in dense city centers: concrete and glass surfaces trap and radiate heat, driving up local temperatures during summer months. A hedge-covered facade at this scale reduces that effect, cooling the building and its immediate surroundings, while also supporting local biodiversity by giving insects and birds somewhere to live in the city center.
The sustainability credentials go beyond the facade. Kö-Bogen II received pre-certification at the Platinum level from the German Sustainable Building Council (DGNB) - the organization's highest rating - and construction relied on a resource-conscious "lid construction" method, allowing the foundation and structural elements to be built in parallel rather than in strict sequence.
Part of a Larger Vision for the City
Kö-Bogen II sits alongside two other Ingenhoven projects that together complete a long-term redesign of this part of Düsseldorf: the austere Dreischeibenhaus and the lighter, more buoyant Schauspielhaus. As the studio's founder, Christoph Ingenhoven, has described it, each building represents its own era and approach, without competing with the others - together they mark the end of an ambitious piece of urban renewal.
Giving as much greenery back to the city as possible has run through Ingenhoven's work for decades, across multiple climate zones - the studio calls this approach supergreen®, treating sustainable, integrated design as a starting principle rather than an add-on. It echoes our piece on Passivhaus design - buildings engineered from the ground up around energy performance, not appearance. The deZZign team admires what the architects pulled off here: Kö-Bogen II solves a real urban problem instead of only looking good.
Green Facades and Roofs on a Private House
The scale of Kö-Bogen II is out of reach for a private home, but the principle is not. The simplest option is an extensive green roof of sedums and grasses: a thin growing layer, low weight, and minimal maintenance. An intensive roof with lawn, shrubs, or even trees needs a stronger structure and irrigation. On walls, climbing plants on cables or trellises are the most reliable choice; modular living walls look spectacular but need constant watering and care. Either way, the greenery has to be designed in from the start: structural load, waterproofing with a root barrier, drainage, and safe access for maintenance.
In Seattle, green roofs also help manage stormwater, which matters in a city with long rainy seasons, and many new developments must meet landscape requirements under the city's Green Factor program. Native and drought-tolerant plants handle the wet winters and increasingly dry summers best. See our article on biophilic design in Seattle and our landscape design and passive house and sustainable design services.
FAQ
How many plants are on the Kö-Bogen II facade? More than 30,000 hornbeam plants forming about 8 kilometers of hedge. The architects estimate their effect at roughly that of 80 mature deciduous trees.
Can an ordinary house have a green roof? Yes, if the structure is designed for the extra weight. A lightweight extensive roof suits most flat and low-slope roofs, but the decision belongs at the design stage.
