Wetland roofs

Question 1:
How is the cooling effect in the rooms and the wetland roof achieved? See answer

Question 2:
How high is the temperature set back? See answer

Question 3:
What are the criteria for plant selection? See answer

Question 4:
How much is the static load onto the roof? See answer

Question 5:
How it is the supply with nutrients achieved? See answer

Question 6:
How does your irrigated wetland roof survives under occasionally periods without any precipitation in summer, so that the rainwater cistern gets dry and is not replenished on time? See answer

Question 7:
Where is your cistern  situated in your floating treatment wetlands? See answer

Question 8:
What kind of maintenance for the system is needed? See answer

Question 9:
What are the cost of an irrigated wetland roof? See answer

Question 10:
What is the vision of such a wetland roof? See answer

Question 11:
Did you publish with respect to wetland roofs? See answer

Question 12:
Is there any research and development concerning this topic? See answer


Answer to question 1

How is the cooling effect in the rooms and the wetland roof achieved?
At high temperatures and a high water-vapor deficit of the air, terrestrial plants close their breathing pores (stomata) and thereby reduce transpiration.  This mechanism is not necessary for marsh plants (helophytes), because they live regularly at water saturated soils. Their transpiration, which goes up to 30 l /m² x d in a reed ecosystem, results in a high evaporation-based cooling.   

 


 

Answer to Question 2

How high is the temperature set back ?

ca. 8° - 10 ° C . It makes a big difference, if you have to work or sleep at 20 °C or 28°C.

 


 

Answer to question 3

What are the criteria for plant selection?

The coefficient of leaf area should be as high as possible to initiate a high evaporative cooling effect (evapotranspiration). Therefore we plant as main constituents of  our plant selection species from the genera Carex ssp. and Juncus ssp.  Aquatic macrophytes like Phragmites, Typha and Glyceria are very seldom used, although they would maximize the cooling effect by evapotranspiration by their  large aboveground biomass. Because of their height of 1.5 m - 3 m they are prone to windthrow on a rooftop. For aesthetical reasons we also add attractive flowering marsh plants like Caltha ssp., Iris ssp., Lythrum ssp., Mimulus ssp., Valeriana ssp., Mentha ssp. and others, depending on which continent the construction site is situated. Thus they are also a valuable food source for butterflies, wild bees and bumblebees.

 


 

Answer to question 4

How much is the static load onto the roof?

Its about 20 - 25 kg/m², that is much less than for most of the other green roof types. We use no substrates like sand, gravel and soil; only the water storing textile mats and the plants generate the roof load.  

 


 

Answer to question 5

How it is the supply with nutrients achieved?

By dry deposition from the air and by application of liquid nutrients into the cistern from time to time. If the origin of the irrigation water of the wetland roof is polluted rainwater, greywater or industrial wastewater, it serves as nutrient source.

 


 

Answer to question 6

How does your irrigated wetland roof survive under occasionally periods without any precipitation in summer, so that the rainwater cistern gets dry and is not replenished on time?

For such situations an emergency supply of drinking water or greywater into the cistern should be provided in the construction design.

 


 

Answer to question 7

Where is your cistern  situated in your floating treatment wetlands?

It is integrated into one of the Paolo Timber pontoons.

 


 

Answer to question 8

What kind of maintenance is needed for the system?

Maintenance requirements are generally low. If the irrigation computer or the pump fails this will be signaled by an optical or acoustic alarm. It may happen that tree seeds were dispersed by the wind onto the rooftop. They should be eliminated (once in three years), because the insulation liners are not resistant to tree roots. It is not necessary to mow the marsh plants on the plant carrier vegetation mat.
Rubbish like leaves should be displaced from the filters (sieves) of the cistern (at least four times a year). If the marsh plants on the rooftop are getting yellow colored, the irrigation water should be fertilized (N-P-K), normally one to two times a year.

 


 

Answer to question 9

What are the cost of an irrigated wetland roof?

You should calculate roughly using the figure 50-60€/m², depending on the features and the type of roof (flat- or sloping roof).

 


 

Answer to question 10

What is the vision of such a wetland roof?

Today more than 50% of the world population is living in overheated urban and suburban areas. This number is constantly increasing. Instead of some small scale pilot projects, we have the aspiration towards a mass use of green roofs, so that they get relevant for the urban climate. In megacities like Mexico-City, Shanghai, Singapur, Neu-Dehli, Ho-Chi-Minh-City etc. only the huge areas of the roofs are available for greenery. We try to convince local city administrations to enforce laws for obligatory green roof covers for at least 50% of the buildings.
 


 

Answer to question 11

Did you publish with respect to wetland roofs?

Yes, there are some papers on our homepages (go to "wetland roofs" ; go to "publications"), but see also the following publications:

Blumberg, M. (2019): Sumpfpflanzendächer aus der Sicht des Planers - Grundlagen und Perspektiven aus der Praxis. In: Zehnsdorf, A., Trabitzsch, R. (Hrsg.) Sumpfpflanzendächer – Themenheft zum Projekt Forschungsgründach. Helmholtz-Zentrum für Umweltforschung, (ISBN 978-3-944280-07-3), S. 30 - 41.

 

Zehnsdorf, A., Willebrand, K. C. U., Trabitzsch, R., Knechtel, S., Blumberg, M., Müller, R. A. (2019): Wetland roofs as an attractive option for decentralized water management and air conditioning enhancement in growing cities - A Review. In: Water2019, 11(9), 1845; https://doi.org/10.3390/w11091845.

 

Zehnsdorf, A., Blumberg, M., Müller, R. A. (2019): Helophyte mats (wetland roofs) with high evapotranspiration rates as a tool for decentralised rainwater management – process stability improved by simultaneous greywater treatment, in Water Supply (2019) 19 (3): 808-814.


Zehnsdorf, A., Blumberg, M., Müller, R. A. (2018): Helophyte mats (wetland roofs) with high evapotranspiration rates as a tool for decentralised rainwater management – process stability improved by simultaneous greywater treatment, Water Science and Technology: Water Supply, Dezember 2018

Zehnsdorf, A., Stock, N., Richter, J., Blumberg, M., Müller, A. R. (2016): Grauwasserreinigung mit einer Sumpfpflanzenmatte unter Praxisbedingungen, in Chemie Ingenieur Technik, 88, No. 8, 1138-1144.


Blumberg, M. (2011): Sumpfpflanzendächer als Variante der Dachbegrünung, in
GWF Praxiswissen, Band 1, Regenwasserbewirtschaftung , ISBN 978-3-8356-3257-8.


Blumberg, M. (2010): Sumpfpflanzendächer, eine besonders vielseitige innovative Variante der Dachbegrünung, in GWF Wasser Abwasser, 151. Jahrgang / Heft 6, Essen, S. 568-571.

 


Answer to question 12

Is there any research and development concerning this topic?

Yes, since this year (2014) we started laboratory trials together with the Helmholtz Centre for Environmental Research in Leipzig to test the efficiency of irrigated wetland roofs for wastewater treatment.