Foto: Michal Šperling
House with a wetland roof in Prague
Jury Award in the Adapterra Awards 2019
Only a few people would expect a family house in the courtyard of Prague city centre. Yet one of them stands in Letná in Prague, the capital of the Czech Republic. Moreover, it is a passive building with a roof covered by lush vegetation which serves as a wetland wastewater treatment plant. Greenery also surrounds the house. Vegetable beds and fruit trees give the impression that you are not in the city center at all. Tall houses protect the courtyard from noise and the green oasis with its evaporation lowers the temperature during hot days and humidifies the air.
The Adaptation Journey
The positive impact
Compared to the surrounding roofs which in summer heat up to 80 ° C, wetland plants on the green roof maintain a temperature of around 24 ° C. Together with the surrounding greenery in the courtyard, it helps to lower the air temperature and thus fights the effect of the thermal island in the city. It also prevents the rapid runoff of rainwater and provides a living space for butterflies, bees and other insects.
Wastewater treatment and reuse saves more than 40% of drinking water consumption. Furthermore, the combination of a ground heat exchanger for heating and solar panels on the roof lowers the energy consumption too.
How does it work?
The passive house with a wetland roof was built in Letná in Prague on 470 square meters of land in 2016. The owners' vision was to build an environmentally-friendly house. Therefore, they decided to build a passive house.
The air is cooled in summer or preheated in winter in a 40-meter ground heat exchanger. The air supplied to the house helps to make the microclimate inside more humid. The used heated air then helps to dry, for example, clothing used for sports. The solar panels placed on the roof heat the water for the house. Only recycled water is used for flushing the toilets and also for watering plants.
The wetland root sewage treatment plant located on the roof next to the solar panels saves more than two fifths of the consumption of drinking water. At the same time, the wetland area of 80 square meters improves the microclimate of the surroundings. At the temperature of 30 ° C, up to 300 liters of water per day evaporate off the roof.
Until 2016 the plot in the courtyard was unused and overgrown.
Operation and maintenance
The running costs consist of routine maintenance of the technology, regular mowing of the green roof and cleaning the separation tanks of the constructed wetlands. It is around 1000 CZK (40 EUR) a year.
The house is an inspiration thanks to the air, energy and water management systems. The biggest benefit is the possibility to use wastewater for irrigation of roofs, facades and wetland flower beds in cities. A very nice surprise is the amount of bees, bumble bees and butterflies that fly on the roof in the city center.
Obstacles and challenges
One of the challenges during the construction was the delivery of the necessary machinery into the courtyard. Fortunately, it was possible to enter through a different part of the courtyard. This is how the smaller machines were taken in, and then got transferred by a crane over the wall dividing the courtyard into two.
How much did it cost?
To build the house, the owners used their own finances and grants from the Green Savings Programme. The total costs reached about 10 million CZK (400 000 EUR), the costs associated with the air, energy and water management systems were around 600 000 CZK (23 000 EUR).
The expected return of the investment is within 20 years, the lifetime of the investment is twice that. The savings reach 15 000 CZK (590 EUR) per year.
Family and apartment houses Water purification and recycling Use of rainwater Heating Green roof Biodiversity Heat waves and thermal island Floods and torrential rainfall Lack of water and drought