Urban farming on Faculty roof

The roof of the C/D lecture hall at Civil Engineering and Geosciences, may be growing crops this spring. Last week a 500 m2 green roof was fitted on top of a 60 mm deep layer that collects and stores rainwater. This water catchment, right beneath the green roof, allows more plants than just sedum to grow.

(Illustration: www.polderdak.nl)

The roof is designed to collect water during heavy rain showers and thereby relieve the drainage system, explains researcher Olivier Hoes. Between the roof and the gutters is a valve with sensors that controls the amount of water contained. “If we do not need to use the water for the roof or for any other purpose, we can drain it after the rain shower.” Hoes wants to see if Buienradar, the rain forecaster, can be used to determine in advance whether water on the roof needs to be drained.

Adjacent to the C/D lecture hall is A/B lecture hall which has an identical roof. This roof has not been fitted with a green blue roof, but will be fitted with measuring equipment for reference measurements. The comparable information generated will show the added value of the polderdak, which is financed by the European Institute of Innovation and Technology EIT Climate-KIC.

Hoes plans to measure the quantity of precipitation, the temperature on and just below the roof, the wind, UV rays, the water drainage and the temperature of the ceiling of the lecture hall. Measuring the temperature of the ceiling will show if the polderdak keeps it cooler or not and if so, by how much. “Our research will show whether the argument in favour of green roofs to keep buildings cool makes sense.”

Hoes also wants to know the extent to which it is possible to farm close to homes. “It is fantastic to use such a large roof to grow crops and have a roof terrace.” Researcher Lexy Ratering Arntz and Hoes will soon look into what crops to plant. “Millet and hops should be fun,” jokes Hoes. Ratering Arntz suggests “strawberries and lettuce”. They are still looking for eager students to form an urban farming team.

The perimeter of the roof will have perennial plants which the researchers will not work with. They are there “so that you keep away from the edge of the roof” explains Hoes. Containers with various crops will be planted in the large central area. There are fences for safety. “You may only approach the edge in an attached safety harness. Should you fall off by accident, you’ll just dangle there.”

The polderdak is part of the WaterStraat in the Green Village and will eventually capture 60 litres of water per square metre. “Calculations have shown that the existing construction can bear this amount,” says Hoes. “The only thing we must not do is have 50 people coming at one time to see how wonderful it is. We have built a platform and a roof terrace in a corner for groups to come and see.”

Hordes of visitors to the roof terrace have to wait. A steel staircase still needs to be delivered and asbestos has been found in the drain of the reference roof. According to a TU Delft spokesperson, the asbestos is in the part of the drain that is in the ground. This part has been closed off and will be decontaminated.

Smaller versions of the polderdak are being tested with other universities in four locations in Italy. “They have dryer periods there,” says Ratering Arntz. “We plan to collect comparable data to see how they affect the roofs. We will then be able to optimise the system for different climates.”