Green roof

from Wikipedia, the free encyclopedia
Green roof of Friedensreich Hundertwasser's stone house , part of the Rogner Bad Blumau hotel complex
Green roof house

The roof is a form of Bauwerksbegrünung and refers to both the process of Bepflanzens of roofs in the form of roof gardens (or the omission overgrowing after appropriate fitting-out) as well as the entirety of the existing plant , including the necessary substructure on a green roof. It is a possible component of ecological building .

description

In terms of ecology , green roofs are considered to be a settlement biotope that plays a role in particular in terms of the local climate and rainwater management. A distinction is made primarily according to the type of vegetation between extensive (thin layer structure with substrate, drought-compatible vegetation) and intensive (full-fledged soil structure up to tree planting possible) roof greening.

In Germany, green roofs are partially publicly funded. This can be done through direct grants, stipulations in development plans or indirectly, by splitting the wastewater charges.

The following guidelines can be used for the structural implementation:

Guideline for the planning, execution and maintenance of green roofs of the Research Association Landscape Development Landscaping  eV in Bonn (short: FLL green roof guideline )

Guidelines for the planning and execution of roofs with waterproofing (short: flat roof guidelines ), part of the technical regulations of the Central Association of the German Roofing Trade (ZVDH).

In Austria, ÖNORM L1131 (greening of roofs and ceilings of building greening) has been valid for green roofs since June 2010 .

A historical form of green roof is the sod house . The Austrian artist Friedensreich Hundertwasser was a big proponent of green roofs, who saw them as an important part of the reconciliation between man and nature he was striving for. He also designed several house types with green roofs, in particular the Hügelhaus, the Augenschlitzhaus and the Grubenhaus, which was later realized as the Waldhofhaus.

Advantages and disadvantages

Advantages:

An extensively green car park roof
  • Protection of the roof waterproofing and almost doubling of its service life, as mechanical protection is created and the UV radiation is absorbed .
  • Improvement of the indoor climate . Due to the evaporation of the stored rainwater, the indoor climate of the rooms directly below can cool down in summer. This means that an air conditioning system may be dispensed with. Due to the insulating effect of the green roof layer, the rooms below cool down less in winter. Depending on the version, a green roof corresponds to an insulation material of up to 80 mm thick from the thermal conduction group (WLG) 040
  • Water retention. Since a green roof evaporates more than half of the annual precipitation, urban drainage and sewage treatment plants are relieved.
  • Improvement of the urban climate . Green roofs can filter dust and pollutants from the air. In addition, the heating of the city is counteracted by the numerous sealed surfaces.
  • Replacement habitat . New habitats can be created for rare animal and plant species - for example birds and butterflies. In Berlin, more than 50 different types of honey and wild bees were counted on green roofs.
  • When combined with photovoltaic elements, the cooling effect of the vegetation increases the efficiency of the PV system.
  • Visual upgrade of the building.

Disadvantage:

  • Depending on the manufacture, the acquisition costs may be high.
  • The roof needs to be looked after. It may be necessary to cut back bushes and apply substrate.

Urban climatic effect of green roofs

Green roofs of the Arche eco-house in Frankfurt am Main

In urban areas, the air temperature is higher than in the undeveloped surrounding areas. The causes are manifold and lie primarily in the high heat capacity of the building fabric, which also reduces the exchange of air , and in the reduced evaporation. In addition, there is the release of heat from traffic, industry, trade and private areas as well as the higher atmospheric counter-radiation due to the increased aerosol content in the city air. The buildings and the sealed road and path areas give off the heat stored during the day to the environment at night, so that the temperature differences are most pronounced in the evening and night hours, with radiant weather conditions of up to 10 ° C. Due to their high proportion of the urban area, roof areas play an essential role in the development of these temperature differences. Greening the roof surfaces can influence the air temperature, humidity and radiation conditions in the immediate vicinity, as has been proven in various measurements.

Green roof of Chicago City Hall

In the summer months, the short-wave radiation on the building surface is reduced because the plants absorb and reflect a large part of the radiation. Another effect is the cooling due to water evaporation on the leaf surfaces with the resulting evaporation cold . Measurements showed temperature differences of 10 ° C on the surface of green and non-green roofs in the midday hours of the summer months. These effects are greater with intensive green roofs than with extensive green roofs, since the larger plant mass creates more surface and the larger soil volume can provide a higher water supply.

In particular, green roofs can compensate for the daily cycle, especially attenuating the high level of heating in the middle of summer. In long-term evaluations of results, this effect “blurs” so that, for example, the annual mean calculations show only slight temperature differences of a few degrees between green and non-green roofs. Facade greening through the shading and the increased evaporation cooling also contribute to reducing the heating in summer.

Occurrence of green roofs in Germany

No comprehensive surveys are available on the distribution of green roofs in Germany, so that only estimates are possible. According to a survey of its members, the Fachvereinigung Bauwerksbegünung (FBB) assumes an annual expansion of around 8 million m 2 of green roof areas, over 80% of which is extensive greening. In recent years, the proportion of intensive greening has increased, especially through the greening of underground car parks.

A comprehensive survey of green roofs is available for the city of Düsseldorf from 2008. After that, approx. 730,000 m 2 of green roof area was 1.6% of the total of 25 km 2 of roof area. The green roofs are distributed throughout the city, including 1,330 house roofs with a total of 440,000 m 2 and 350 green underground car parks with a total of 290,000 m 2 . This green roof corresponds to around 10% of the green spaces available in Düsseldorf.

In Stuttgart, 180,000 m 2 of green roof area was created between 1986 and 2008 through funding of up to 50% of the costs on public and private roofs. In the land use plan 2010, a further 1.5 million m 2 of green roof area is planned for future construction projects as a minimization or compensation measure.

Funding and guidelines for green roofs in Germany

The promotion and further dissemination of green roofs is part of the planning and decision-making processes under building law that are assigned to the municipalities in Germany. There are essentially three instruments to choose from: guidelines in the land-use planning, a split wastewater fee and financial support.

Green roofs can be specified in a development plan for flat sloping and flat roofs and counted as an ecological compensatory measure in accordance with Section 1a (3) BauGB, from which, according to a survey by the DDV in 2009, around 90% of the new green roofs originated. The basis is the Building Code, BauGB, with Section 9 (1) No. 20 and No. 25 a and b).

With the split wastewater fee, the costs for wastewater and rainwater are determined separately. The retention of rainwater on green roofs has a relieving effect and can be financially beneficial for building owners, provided this effect is taken into account in the fee structure. According to surveys by the German Roof Gardeners Association, the average savings are EUR 0.46 per m 2 of greened roof area and year. A maximum of 1.12 euros per m 2 of greened roof area per year could be saved, as the example of Cologne shows.

In addition, financial support programs are used, for which, however, there are no nationwide uniform guidelines. In Germany, the subsidies for green roofs with an average of 10-20 euros per m 2 in promoting pro rata the upper limit is usually 50%.

Structural requirements for green roofs

Green roof house in Poland

An essential prerequisite for the green roof is the load-bearing capacity of the roof construction, as additional loads may have to be absorbed and safely removed. In the case of new buildings, this additional burden can already be taken into account in the design; In the case of existing buildings, the usable reserves of the load-bearing capacity must be checked technically. The two basic types of roofs - warm and cold roofs - have different suitability for green roofs due to their construction:

  • The warm roof consists of a single-shell, therefore non-ventilated construction with or without thermal insulation and is basically suitable for green roofs, whereby the following construction details must be observed.
  • The cold roof consists of a double-shell, rear-ventilated construction, the outer skin of which usually has a light structure with low load-bearing reserves. This type of roof is only suitable for extensive green roofs in existing buildings, whereby the following construction details must also be observed (see below).

The thermally insulated construction of the inverted roof and the duo or plus roof with thermal insulation above the seal are suitable for both extensive and intensely green inverted roofs. With this construction, suitable drainage layers are necessary for safe drainage of rainwater.

Sectional drawing of the green roof

If there is sufficient load-bearing capacity, all types of greening with the respective types of vegetation can be created on cold roofs, including intensive greening with their higher loads. In the case of a roof structure without thermal insulation in open structures, temperatures below freezing point can occur on the underside, which can lead to frost damage to the vegetation of the green roof. For these applications (ceilings over parking and delivery areas or parking lots), only frost-hard plants should be used.

With a low reserve of load-bearing capacity (cold roof with a light shell), extensive types of green roofs are possible. Special green roofs with very low additional loads are available for these roof systems, which are mainly used in industrial construction. The weight-optimized substrates and special drainage elements developed for this only provide an additional load of 40 to 80 kg / m 2 . Since the existing or otherwise required to protect the roof sealing gravel fill with its usual surface loads of 60 to 120 kg / m 2 can be omitted, the corresponding load-bearing capacity is free.

Construction of a green roof

The long-term use of a green roof requires the protection of the roof membrane and a stable, appropriate structure of the vegetation area. The required layer structure for the green roof is subdivided as follows (from the roof waterproofing to the "top"):

  • Protective layers of the roof skin through a separating layer, through a root protection and a protective layer and
  • vegetation-technical layers with the drainage layer , the filter layer and the vegetation layer.

The tasks of the individual layers can be achieved through material combinations so that multi-layer laying systems reduce the workload. With extensive greening, two-layer construction methods are used for the vegetation-technical layer. Most construction methods require protection against root penetration in order to prevent damage to the roof membrane from penetrating plant roots. It is therefore necessary for both intensive and extensive green roofs, unless the existing roof waterproofing is already root-proof, e.g. B. EPDM seals . This material meets all the requirements for root resistance, is free of herbicides and pesticides and does not evaporate plasticizers. It is also light and thus reduces the weight load on the roof.

Layers of a green roof

The separating layer protects the roof waterproofing from chemical incompatibilities resulting from the protection against roots. For this purpose, geotextiles such as fleece are usually laid.

The root penetration is done either by laying plastic sheets ( PE , PVC , polyolefins ), EPDM geomembranes or and floors or by a continuous liquid seal on polyurethane - (PUR), polymethyl methacrylate - (PMMA) or polyester base resin (UP). It is important that the sheets are laid precisely and densely, and should be raised up to 20 cm above the vegetation layer at the edges in order to prevent the roots from "growing around" the protective layer. A vegetation-free strip of gravel , crushed stone or slabs should be created at roof drains and rising components , which also simplifies care and maintenance work.

A protective layer is placed over the root protection to prevent mechanical damage. This layer must be correspondingly resistant to mechanical, thermal and chemical loads. Geotextiles, such as fleeces, are suitable for light loads. In the case of heavier loads, building protection mats made of rubber granulate or plastic granulate as well as drainage mats and plates are used, which also take on the drainage function. With very high loads, protective layers made of concrete (slabs) or mastic asphalt make sense. The drainage layer takes the excess water from the vegetation layer and passes it off to waterlogging to prevent. With the appropriate material, it can store water and, in the case of the “with water accumulation” type of greenery, serve to store water. Drainage layers are formed from bulk materials (gravel, lava , expanded slate and pumice ), from recycled bulk materials (broken bricks) or laying systems (drainage mats, drainage plates or combined drainage and substrate plates). The material is selected according to the type of greenery and the respective structural conditions. The materials must be weatherproof and resistant to microbial decomposition in order to ensure long-term drainage.

The filter layer retains finer components washed out of the substrate layer from being transported further into the drainage layer below in order to prevent silting up. Geotextiles, for example nonwovens or woven fabrics, are used as material, which are laid as webs over the drainage layer made of bulk materials or are already incorporated as components in drainage mats. The geotextiles should be rootable in order to use the drainage layer as additional root space, especially in the case of extensive greenery with its low layer thickness.

The vegetation layer creates the rootable space for the plants with substrate mixtures, which should find an adequate supply of nutrients and water as well as possibilities for anchoring in the soil. The choice of substrates depends on the type of greenery chosen, the type of vegetation required and the structural conditions. When selecting the substrate, the water storage capacity is important, which should be over 45 percent by volume for intensive green roofs and 35 percent by volume for extensive green roofs, but not higher than 65 percent by volume.

Vegetation on green roofs

The plant community of green roofs is subject to high demands, as they have to cope with high radiation intensities, dry periods , waterlogging , nutrient starvation and periods of frost. Therefore monocultures should be avoided; Mixed societies can better adapt to changing site conditions. In the green roof guidelines of the Research Association for Landscape Development Landscaping (FLL, 2008), the site conditions are divided into four groups: climatic, weather-related, building-specific and plant-specific factors. In detail, the substrate properties, the roof pitch, the exposure of the roof surface, the regional climatic conditions and the amount of precipitation as well as the sunny and shady areas of the roof surface are taken into account.

Extensively green roof garden

Mosses , succulents (water-storing, mostly thick-fleshed plants from arid regions), herbs , grasses and occasional onion and bulbous plants are mainly used for extensive greening . The names of mixed cultures begin with the most strongly represented group of plants. For extensive green roofs, moss- sedum , sedum-moss-herb, sedum-herb-grass and grass-herb associations are common. Moss-sedum greening can be used with substrate thicknesses of only 2 to 6 cm, the plants are highly resistant to drought. Grass-weed greening requires substrate layers of at least 10 cm for sufficient growth and form a " semi - dry lawn or dry lawn society ". The grass-herb greening represents the transition to the vegetation forms of the simple intensive greening . The costs for an extensive roof greening start at 25 to 35 € / m 2 according to the information of the German Roof Gardeners Association

Use of solar energy and green roofs

The combination of solar collectors and photovoltaic modules with a suitable green roof is possible. The heat and sound insulating effect of the green roof can be combined with the effect of solar cells.

literature

  • Susanne Bossler, Bernd Suszka: Vegetation and substrate on roofs in Osnabrück. 1987 Diploma thesis at Osnabrück University of Applied Sciences, Department of Land Management.
  • Susanne Bossler, Bernd Suszka: Spontaneous vegetation on roofs in Osnabrück. In: The Garden Department. 37/1988, pp. 209-223 .
  • Federal Agency for Nature Conservation (BfN) (Hrsg.): Roof and facade greening - new habitats in the settlement area. Facts, arguments and recommendations. Bonn 2019, ISBN 978-3-89624-276-1 (free download)
  • Walter Kolb, Tassilo Schwarz: Green roofs - intensive and extensive. Eugen Ulmer, Stuttgart 1999, ISBN 3-8001-5075-1 .
  • Manfred Köhler, Georg Barth, Thorwald Brandwein: Facade greening and roof greening. Eugen Ulmer, Stuttgart 1993, ISBN 3-8001-5064-6 .
  • Bernd W. Krupka: Roof greening. Use of plants and vegetation in buildings (= landscape design handbook). Eugen Ulmer, Stuttgart 1992, ISBN 3-8001-5051-4 .
  • Roof + green. Trade magazine for building greening. Roof, facade, interior. 4 issues a year, published since 1992. Verlag Dieter A. Kuberski, Stuttgart, ISSN  0943-5271 .
  • Roland Appl, Reimer Meier, Wolfgang Ansel: "Green roofs in modern urban architecture". IGRA Verlag, Berlin 2009, ISBN 978-3-9812978-1-2 .
  • FLL , "Guideline for the planning, execution and maintenance of green roofs" Bonn 2008, (German + English) ISBN 978-3-940122-08-7 , DIN A4 brochure, 118 pages.
  • Nicole Pfoser, Nathalie Jenner et al .: Green building energy. Potentials and interactions. Final report research project Zukunft Bau. ISBN 978-3-940122-46-9 , ( free download ).

Web links

Commons : Green roofs  - collection of images, videos and audio files

Individual evidence

  1. ↑ Saving energy with green roofs
  2. ↑ University City of Marburg supports green roofs , City of Marburg, accessed on October 9, 2018
  3. ^ W. Kuttler: Urban ecology: a textbook for study and practice . Ed .: H. Sukopp, R. Wittig. Gustav Fischer Verlag, Stuttgart 1998, urban climate.
  4. ↑ a b K. Höschele, H. Schmidt: Climatic effect of a green roof. Garden and Landscape, No. 6, pp. 334–337, 1974.
  5. ↑ M. Köhler, M. Schmidt: Courtyard, facade and roof greening - a central component of urban ecology. 12 years of experience with a greening utopia. Landscape development and environmental research, series of publications in the Department of Environment and Society No. 105, TU Berlin 1997.
  6. ↑ K. Holzmüller: Naturally climate protection - green roofs in Düsseldorf, financial support and quantitative aerial photo evaluation. In: R. Appl (Hrsg.): Green roofs in modern urban architecture. Proceedings International Green Roof Congress Nürtingen, International Green Roof Association Berlin 2009.
  7. ↑ J. Döveling: Two decades of green roof funding in Stuttgart - a field report. In: R. Appl (Hrsg.): Green roofs in modern urban architecture. Proceedings International Green Roof Congress Nürtingen, International Green Roof Association Berlin 2009.
  8. ↑ a b c d e W. Ansel: Guidelines for green roofs for municipalities: Benefits, funding opportunities, practical examples. German Roof Gardeners Association (DDV) eV Nürtingen, 2011.
  9. ^ W. Ansel: Green roof funding in Germany - Proven procedures and current trends. In: R. Appl (Hrsg.): Green roofs in modern urban architecture. Proceedings International Green Roof Congress Nürtingen, International Green Roof Association Berlin 2009.
  10. ↑ a b c d e f g h i j k l Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau, FLL (Ed.): Guideline for the planning, execution and maintenance of green roofs. Bonn 2008, ISBN 978-3-940122-08-7 .
  11. ↑ Sealed roof with EPDM. - EPDM. Accessed January 21, 2020 .
  12. ↑ Costs for an extensive green roof
  13. ↑ Nature protection on green roofs in connection with solar systems. Archived from the original on September 20, 2016 ; accessed on January 11, 2018 .