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Urban Rooftop Gardening

Presented By

Ahmed M. Behgat
Estifanos Kiflu
Georg Kirbis
Mohamed Gad

Environmental Problems
- air condition harms health
- dramatic water shortage

Cairo 2012 - Dokki

Our Idea: Gray to Green

At first sight it is a regular Urban Rooftop Garden, but after a closer look, you can see the innovation. It recycles grey water. 

Water Cycle

1. Collect gray water from any source of the house

2. Transport water on top of the roof

3. Relief water into a basin --> water evaporates

4. Condensed water flows into the plant trays 

5. The water can be used to water urban gardens
Green waterproof Rooftop

First approach: SUDU Project (waterproofing roof)

The roof construction follows again a vaulting technique, similar to the ceiling, but this time using bigger loam bricks. As the demands of a roof as an exterior element are different from those of a ceiling, it is covered with a special 10cm thick waterproof mortar, produced out of prickly pear cactus juice, salt, lime and loam soil. Since 2008, this method has been again implemented by an Ethiopian born artist, Meskerem Assegued, in a project in the village of Harla, near by the city of Dire Dawa, in Easternmost Ethiopia. She investigated the technique in Mexico and brought it back to Ethiopia, where she found historical evidence that it was used for centuries before falling into disuse and then forgotten.


Grey water treatment methods  

minerals used as filters, especially all sorts of desert sand
-  plants used as filters
evaporation that separates water and soda/soup
 Condencing system.

Grey water is wastewater from a household that does not contain human or animal waste. If properly collected and filtered, it can be used to water ornamental plants or plants that are not used as a food source. Grey water is alkaline due to the detergent content, so plants that live in alkaline soil with large root systems are the best plants to absorb grey water. The Ph of greywater can range from 6.5-8.7.

System illustrated beside is being used to evaporate water only by sun rays as source of energy. Set of black painted hoses, mirrors combination and solar heater are used in series to evaporate water. Also an anti bacteria paint is used in the solar heater. 

Low Tech & Low Budget Water Distiller

Visualization of Ideas to pump/treat gray water

 First Idea:

 Water will be pumped of the roof and there evaporate in a simple water distiller

 Next Idea:

 Water flows down slowly the outer wall of the house and by that the sun can heat up the pipes so a certain amount of water can evaporate and steam up on top of the roof, where it condenses.


1: water that gets pumped into the evaporation area (pot)

2: old satellite dish

3: reflecting material (example)

4: Solar pot which would hold the water that slowly gets heated up and evaporates

5: pipe that relives the evaporated water

Idea: this could be an effective way to evaporate  gray water and it could also be quite easy to clean out the pot every once in a while. Maybe this could even be quite inexpensive (example)

Another sketch that shows the same idea. It is unnecessary to use an old satellite dish. (example)

An idea i came up with, after i rethought the whole projekt: 


This is a solar energy based water generator, which works with the principle of a fridge. Through water condensation on colder surfaces, water can be collected. Further information: Skywater Project or Eole Water

My thoughts: 

This Design reduces the ongoing project to further simplicity. Instead of using gray water, now the water for the urban rooftop garden gets generated itself without adding to the electricity bill. This way it the urban rooftop garden system gets more interesting for anybody. I thought that most people would hesitate to rebuild their grey water cycle just for a bit of gardening on their roof. The costs to do that would probably scare a lot of people. The urban rooftop garden would work fine without having pipes all across the roof to supply the plant pots with water automatically. It rather is a positive user experience to actually water the plants by hand, instead of an automated system. This will reduce the costs and make the whole design less fragile.  


What kind of soil is in a large and cheap scale available in Egypt/Ethiopia/Germany?

Ethiopia and Germany:

- Bio waste and fertile soil are available


- Ashes
- Coal
- Sand
- Bio waste
- Nile mud: Until the modern irrigation systems were built the Nile was their only source of irrigation.  Farmers looked forward to the yearly flood.  They set huge basins along the banks of the Nile so that the over flowing water would spill into them.  When the Nile flooded and the water went down it left a layer of  fertile soil. 

How to Create Healthy Soil with organic waste:

No matter what type of soil you have the addition of organic matter will work wonders for its health. Organic matter is plant and animal residues in varying forms of decomposition. It will replenish the nutrients in your soil and improve its texture. You may have heard countless times about adding your leftovers and glass clippings to a compost heap. This is a great idea as your compost is the best form of organic matter. Compost in an advanced stage of decomposition (dark and without smell) is magic for your soil. It encourages microorganism activity causing soil particles to clump together and form aggregates. The aggregates allows for spaces in the soil therefore increasing its drainage. This is especially beneficial for clay soils, which have poor drainage. Other forms of organic matter are animal manure and peat moss. 

If your soil is lacking in nutrients and you don't have access to a compost heap you have a choice of using inorganic or organic fertilizers. Inorganic fertilizers (inorganic salts, manufactured chemically) can be purchased at your local garden and are applied in a dry form that is raked lightly at the base of a plant or in a liquid form. While inorganic fertilizers will work fine they have a number of disadvantages: they release their nutrients too quickly and there is some evidence to show that plants develop a resistance to inorganic fertilizer methods over time, requiring more and more to achieve the same effect. Organic fertilizers are more in tune with nature because they are created from the remains or by-product of an organism. They act slower but they 'amend' the soil rather than the quick 'feeding' it like inorganic fertilizers. Further information (Source)


low-tech/low-energy solution to bring grey water on top of the building. 

A solar-powered pump is a pump running on electricity generated by photovoltaics. The operation of solar powered pumps is more economical and has less environmental impact than pumps powered by an internal combustion engine.

Urban Gardening Systems

Different approaches: 

The plants growing in the roof garden can be come aesthetical and/or eatable.

Listed below are examples of eatable vegitables that can grow using grey water.

 Plant               PH-Level      
 Tomatoes  5.5 - 7.0 
 Lettuce  6.5 - 7.0 
 Strawberries   6.0 - 7.0 
 Onions  6.2 - 6.8 
 Raspberry  6.0 - 6.5 

Source :

 Plants That Like Grey Water | Garden Guides


Grey water can be used to cultivate etable vegitables.Where the edible part of the fruit or vegetable is above ground, and it is eaten raw, the graywater must NOT come into contact with the edible parts.If the vegitable is irrigated by sub-surface dripperline (under a mulch cover), the lettuce leaves will not come into contact with the graywater.

Innovative Aspects

Gray to Green could actually improve certain living qualities in any country, not just Egypt, Ethiopia or Germany. 


- Mega cities like Cairo will have benefits, like a cleaner air, if a lot of roofes would use the Gray to Green system. 
   Plants regulate the air conditions and take dust and fine dust out of the atmosphere. 


- Gray to Green recycles gray water and reuses it right away. This way the water will be used twice and the public water supply will not be stressed as much.  


- just like a regular garden, our urban rooftop garden can be harvested. (refer to Plants)


- Due to the isolating effects of a green rooftop the AC Systems of houses could work more efficient, energy (electricity) would be saved. 
- In countries with cooler climatic conditions green rooftops would also keep the heat inside the house


- Having a rooftop garden will be a good place to rest and recreate. Since Cairo is short on public green spaces, people could start creating their own.