Sequel to the interview about the green wall and roof garden

from left to right: Bas Heessels, *Barry Loerakker, Hugo Rots, Rutger van der Klip, Rob Hopstaken and Walter van de Werken

The green wall
The green wall is located in the atrium. A large hollow space that rises completely through the core of the building and where all floors are visually connected to that green open space. The green wall will contain 52,608 plants.

Walter explains how the choice of plants was made: "The architect Fokke van Dijk of the Central Government Real Estate Agency has certain ideas about leaf structures, appearances, colours and lushness. Together with our internal planting expert, we assess the feasibility of the plan. For example, we look at the available light output in the area, the composition of plant combinations, or whether plants compete with each other. There are a few important contour lines in the wall. These are sharp lines. Then you have to think about which plants are used there. Which type of plant is suitable for this tight contour line and which surrounding plants boost the contour line? Isn't the contour line being overruled by the plants next to it? In addition to the leaf structures and colours, the appearance after pruning is also an issue, what does it look like? Another aspect is, for example, susceptibility to disease. You look at how resistant the selection is and how you can prevent a disease or pest from breaking out in a certain species and that everything is gone at once. All in all, a strategic composition of plants that forms an aesthetic whole."

Sub-frame green wall
"The green wall has a steel sub-frame," says Walter. "It was built from bottom to top at the same time as the steel structure after the core of the building was finished. We chose to make a number of temporary intermediate floors in the atrium to assemble the sub-frame and to install the green panels.”

Rob: "An intermediate floor is actually just a scaffolding construction, horizontally. Because there is a lot of lushness in the green wall, nothing is the same. That is why we had to think about support points for the intermediate floors early on in the process."

The sub-frame is ready, says Walter. "We are now in the process of assembling the green panels. That goes from top to bottom. In order to save time, Rots Maatwerk has already started to assemble natural stone materials on the green wall. In order to be able to plan who does what and when, we divided the work over the segments."

Hugo: "We worked out the entire wall in 3D. There are hundreds of unique steel frames behind it that continuously run in the curves and depths, and the natural stone is precisely tuned to that. Each piece of steel in the frames has its own size and coding. It has to be exactly the right place on the wall or the natural stone will not be placed in the right way. This coordination between wall, plants, steel and natural stone requires a lot of knowledge. That is why 3D design and drawing is the solution. The natural stone of the landscape ribbon is of Belgian bluestone. The stone contains fossils encapsulated in plants, shells and fish, which makes it very lively. No two pieces are the same. By choosing this stone, the lushness also returns in the non-living elements of the green wall, but in a neutral way so that it does not become crowded or dominant. The bluestone has traditionally been used on stately buildings and on buildings with allure. It’s a sustainable material, certainly in the long term.”

“This project is very special because of the many dependencies.”

Lighting of the green wall
"A lot of daylight comes from above, but the intensity doesn't reach all the plants," says Walter. "This means that we have to use artificial light so that the plants remain vital and healthy. Then you have to think about how long and when those lights should be on for a good effect. We've come up with a great solution for turning on the light at certain times of the day. During the day, a rhythm is created in the lamps so that certain parts light up for a moment and then slowly dim." This is called scene lighting, says Rutger. "The lighting then follows the organic lines of the wall. You light up one plant and after a few minutes the lighting shifts to the next plant."

Watering plants
Walter: "We tease the plants a bit by placing them vertically. Then they also have to live on a limited growth layer. You actually keep them alive artificially. That will be done with plant food, water and light. An irrigation system provides them with fertilisers and water. The green wall is divided into segments. In each segment there are sensors that measure how much water is needed."

Bas: "Every segment has a gutter where the excess water is collected. If we wouldn’t do that and only collect water at the bottom, an enormous waterfall would be created. The water for the plants comes from a reservoir in the technical room. The supply is controlled separately for each segment with a pump that regulates the frequency and water pressure." Bas indicates that this was quite a challenge because the segments are interrupted by the shapes of the natural stone.

Walter explains that Koninklijke Ginkel Groep carries out maintenance on the green components and roof garden technology. He explains what maintenance on the green wall entails. "We regularly prune all the plants. That takes about three weeks each time. We do this from a maintenance gondola. There was quite a challenge in that too, because the wall is uneven due to the 3D shape. In addition, we had to design the gondola in such a way that no pruning material falls down in the coffee lounge."

"When people see nature, they're simply more happy."

Living environment
Plants have a positive influence on the quality of the living environment in a building. "Think of humidity and acoustics," says Walter. "Scientific research shows that when people see nature they’re simply more happy. This makes them feel more comfortable. When people feel comfortable, there is less stress. In addition, plants have a cooling effect through evaporation of water."

"We use rainwater in a sustainable manner.”

A smart roof garden
Walter explains how the plants on the roof garden get water: "Under the roof garden is a retention layer with water. This retention layer is controlled by weather data by means of a 'smart' drain. This is called Smart Flow Control. If a precipitation shower of, for example, 20 mm is predicted, the Smart Flow Control measures how many mm of precipitation the retention layer can still store. For example, if this is only 10 mm, 10 mm is transported to a retention cellar, even before precipitation occurs. When it rains, the retention layer is at its maximum. In this way, you will be able to deal with precipitation water in a sustainable way. So in times of drought you can always claim the retention layer. By using the Smart Flow Control, a climate-proof solution has been applied for an excess of rainwater in wet periods, but also for a shortage of rainwater in dry periods. The water from the higher roof comes directly into the retention cellar and can be used if there is a long-term shortage of precipitation. The use of a retention roof in combination with a Smart Flow Control is a robust and innovative way of using water within the regular roof garden technology."

"It all blends together and nothing is even.”

The trees are now in the roof garden on the third floor. You can also see the lush organic forms in its design. Just like the green wall, it is a combination of vegetation and Belgian bluestone. Hugo: "Everything blends together and nothing is even. Even the steel of the planters. The garden is sloping, that changes constantly and its height also changes. Rots is now in the process of paving."

Rob: "They are literally laying a jigsaw puzzle because every stone has a code. There’s a plan where you can see exactly which stone should go where. This has all been thought about in advance."

In the roof garden are also several medicinal plants. "A striking link with the work of EMA," says Bas. "There will also be spectacular seating elements. They are milled from complete tree trunks. Every bench is different because it runs exactly in line with the organic lines of the roof garden."
Hugo made the designs for the seating elements: "They have LED lighting and socket outlets."
Rob: can you imagine installing electricity on a water roof! How is that even possible? That's another reason why we sat around the table."

Insect hotel
"It's also great to mention that there will be an insect hotel on the roof garden," says Bas. "This is an above-ground facility with all kinds of dead organic material, which flying insects can use to make a nest or to hibernate.” Walter adds: “You imitate the conditions in which insects lay their eggs or hibernate. These are normally dead tree trunks or natural caves. We don't have that here in the city, because when a tree is dead, it’s removed very quickly. The great thing is that you now have facilities in that natural garden and that the plants produce nectar so that insects can survive there."

"Mutual trust is at the core of our project," says Hugo. "We have the same ideas and know what to expect from each other. That's our strength."

Bas: "It was an enormous challenge to see to what extent we could fit in with the original ideas of the architect of the Central Government Real Estate Agency and to what extent we had to make adjustments in order to make it feasible.”

Walter concludes by saying that everyone's input is equal: "That's very powerful because if there's a problem, you don't look at who’s problem it is, but you think about a solution together and then you decide which one of us can best solve it. That openness, transparency and trust in each other have enabled us to do this in such a short period of time. I think that's very special about this project and we can be proud of that."

View more pictures of the green wall and roof garden under construction.

*Barry Loerakker is a planning engineer at Construction Consortium EMA and forms the link between design and realisation. A very important role! He could not attend the interview, but is nevertheless in the picture!