GREEN WALLS FOR THE CITY !

Available translations: 

 

Introduction 

The cities growth continues worldwide. Cities merge with others, the number of so called Megacities increases. Some think that cities are the only solution to provide living and infrastructure to the growing world population. They even constitute an ecological chance for the future. A high population density in cities preserves natural spaces and agricultural areas. To keep cities worth living and make them fit for the future, I think, we need to bring back nature, especially plants.

Plants of all kinds contribute to the solution of a variety of negative aspects of traditional designed large cities:

  • Flood risk
  • Urban heat islands
  • Fine particular matter
  • Noise
  • Health of inhabitants
  • Loss of biodiversity

Climate change, which affects city climates above average, fosters some of the mentioned aspects.

The taken measures by planers and decision makers to counteract the mentioned aspects are predominantly conventional. For example, in Vienna a huge sewer tunnel for rainwater (120.000 m³) from highly sealed districts has been constructed in the recent years, to prevent flooding.

A more innovative solution to the problem of fast accumulating and high amount of rain water from these districts would have been the application of plants. Instead of a sewer tunnel a huge area of roof and facade greenings could have accrued to achieve the same amount of water retention.

Background
Roof- and facade greenings are still not applied standardly. There are many reasons for this lack of green in cities. One key to enhance our built environment with natural habitats is better communication of approved technical solutions for horizontal and vertical greening as well as their positive effects to planers and public stake holders. Pilot projects, research and their broad publication would be very helpful in that context.

Another approach would be to oppose the equivalent value of higher living contentment and higher real estate value through roof- and façade greenings to their construction cost, which often constitute a hurdle to application.

Roof Greening
Roof greening is long-established throughout Europe. Construction methods exist for decades. New developments focus on improvement of chosen aspects, as e.g. water retention, weight and thermal insulation. In recent years some trends can be observed, which promote greened roofs. They are applied in planning processes purposefully to achieve e.g. water retention or habitat interconnectedness. Inhabitants appreciate nature – especially within huge cityscapes. Hence, roof gardens are constructed, improving the social sustainability of architecture, raising real estate value providing space for activity and habitats for fauna and flora. Some special planning acts, e.g. throughout Germany since April 2010, foresee roof greenings as means to reduce sewage charge.
Many norms, standards and directive exist concerning roof greenings. The Austrian norm (ÖNORM L1131, 2010) distinguishes four kinds of roof greenings.

Intensive roof greening
All kinds of plants may grow on intensive roof greenings, grasses, herbs, herbaceous shrubs and woody plants including trees! Natural open spaces alike parks on ground level can be realized. There are no vegetation restrictions. They provide a broad variety in design and utilization.
Reduced intensive roof greening
As the name indicates, the variety of applicable vegetation is reduced compared to the intensive roof greening. Predominantly ground covering plants (grasses, herbs, herbaceous shrubs) are recommended. Nutrient and water demand of used species is reduced. Irrigation system is required. 
Extensive roof greenings
Self-perpetuating, near-natural plant societies are initiated on extensive roof greenings. Exclusively indigenous (middle Europe) species of high regeneration capability which comply with the extreme habitat conditions shall be applied. 
Reduced extensive roof greenings
The vegetation base layer of reduced extensive roof greenings is only a few centimeters thick (see table below). Thus, the range of applicable species is limited to sedum and moss plant societies.

Facade greening
Facades represent the largest surfaces of cities. Hence, they bear high potential for greenings, thermal insulation, energy production, etc. Thanks to thermal insulation efforts throughout Europe a vast number of facades is being renovated. It would be very meaningful and efficient to combine the improvement of building physical properties of realties with façade greenings, unfolding maximum socio-economic impact and bringing back nature to the city.<

Types of facade greening 
Three methods of facade greenings can be distinguished:

  • soil-bound
  • plant trough-bound and
  • façade-bound

Plant trough-bound facade greening
The use of plant troughs can be traced back to the ancient world as historical drawings of the Hanging Gardens of Semiramis reveal. Today plant troughs are predominantly applied to balconies, loggias and terraces of apartment complexes to meet the residents demand for nature. Shape, Size and materials of plant troughs vary strongly.

 Accordingly plant troughs may be greened with grasses, herbs, climbing plants, shrubs and small tree species. Due to the limited root zone plants in troughs need irrigation and regular nutrient supply. Thermal insulation of the root zone results in higher vitality and growth rates of the plants.

Disadvantages of plant trough-bound facade greenings in comparison to soil-bound ones are:

  • High cost for construction and maintenance
  • High technical effort
  • Statical problems due to punctual high loads
  • Space demand
  • Lack of root zone, demand for irrigation and nutrient supply

Facade-bound vertical greening
Lack of space or total height of buildings etc. very often prevent soil- and plant trough-bound facade greenings although the facades are cardinally appropriate. Being aware of the multiple common benefits of greenings in cities and the growing demand to adept cityscapes to various challenges (see introduction) some companies developed façade-bound vertical greening systems. Amongst them Patrick Blanc, pioneer and precursor of the façade-bound vertical greening, is best known. He considers his “vertical gardens” are artwork and not vegetation technique. Most competing systems also focus on the implementation of intensive botanical highlights on walls. Only the Grünwand system of company TechMetall from Austria is available with extensive vegetation. 
All systems jointly allow the greening of facades in any desired height, width, combined with thermal insulation etc.
Disadvantages of façade-bound vertical greenings are:

  • High cost for construction and maintenance
  • Highest technical effort
  • Irrigation and nutrient supply system obligatory 

Examples of facade-bound vertical greening system
The following chapter presents exemplary facade-bound vertical greening systems which can be combined with thermal insulation. Of course, the list is no complete survey of all systems on the market since new systems appear regularly (e.g. Fa. Optigrün, Fa. Vertiss). The information given is based on interviews with the system providers and internet inquiry.

The examples show clearly that there are many applicable systems available for architects and building contractors.
The following table gives an overview of the recommended construction thickness for roof greenings in accordance to the desired plant society.

Short profile of facade-bound vertical greening examples




 

product / company

90degreen

applicability

inside, outside

substrate material

Mineral wool, fleece, potting compost

plants

pre-cultivated

type of vegetation

intensive

included technical devices

irrigation and nutrient supply system

cost

Ca. € 500 bis 800 / m²

remarks

Assembly on curtain wall




 

product / company

Techmetall

applicability

inside, outside

substrate material

Potting compost

plants

Sowing / pre-cultivated

type of vegetation

intensive / extensive

included technical devices

irrigation and nutrient supply system

cost

Ca. € 300 bis 700 / m²

remarks

Assembly on curtain wall




 

product / company

Vegetalis / Greenwall

applicability

inside, outside

substrate material

potting compost

plants

pre-cultivated

type of vegetation

intensive

included technical devices

irrigation and nutrient supply system

cost

€ 500 bis 700 / m²

remarks

Assembly on curtain wall




 

product / company

Flexipanel / Sempergreen

applicability

inside, outside

substrate material

Mineral wool

plants

pre- cultivated

type of vegetation

intensive

included technical devices

irrigation and nutrient supply system

cost

€ 350 bis 450 / m² plus irrigation system (ca. € 1000 per wall)

remarks

Assembly on curtain wall




 

product / company

Elata – Helix Systeme

applicability

outside

substrate material

potting compost trough

plants

pre- cultivated

type of vegetation

intensive

included technical devices

irrigation and nutrient supply system

cost

€ 700 bis 900

remarks

Assembly on curtain wall

All shown facade-bound vertical greening systems can be combined with thermal insulation and unfold the plants unique benefits:

  • Enhancement of microclimate (reduction of temperature, increase of air humidity)
  • Protection of the building structure
  • Prevention of building overheating

     

  • Water retention
  • Reduction of particular matter
  • Reduction of noise
  • Storage of carbon dioxide
  • Habitat and habitat interlinking

Conclusion

The field of façade and roof greenings – especially the façade-bound vertical greenings - is very dynamic and promising. The enormous surface potential and the demand for solutions to problems as e.g. urban heat islands, flooding, fine particular matter, loss of biodiversity encourage companies to develop ever new products. Architects and building contractors may choose from a broad variety of reliable systems. Stake holders and public authorities noticed the high potential of façade and roof greenings and their benefits for cities. Façade and roof greenings have to be established in the near future as a standard for urban construction projects of all kinds.

Preliminary to the integration of façade greening technologies in urban planning processes the properties of the systems need to be ascertained scientifically safe and sound.

Probably façade and roof greenings will be applied in future instead of conventional technical solution to certain urban problems as e.g. sewer tunnels or air conditions. Probably façade and roof greenings will be required by law and gouverment-funded to achieve urban planning goals as reduction of temperature highs.