Climate change is having a noticeable impact with rising average annual temperatures, an increase in the number of hot days and a significant increase in the risk of heavy rainfall events. Direct causes of local heat islands are, for example, dense building development, high traffic volumes and a very high degree of sealing, which leads to high temperatures in the Aachen basin, particularly in the summer months.
On 26.08.2020, the City Council of Aachen adopted the Integrated Climate Protection Concept (IKSK) and the climate protection strategy for 2030 contained therein. Among other things, the implementation of the measure (No. 6.8) "Green in the city funding program and campaign" is intended to reduce urban climate deficits. Green roofs and façades are an important measure for adapting to the consequences and effects of climate change.
Green façades and roofs are associated with a wide range of functions and effects that have a positive impact on the urban climate and thus on well-being. In addition to urban planning and aesthetic functions, the building physics, bioclimatic and ecological functions are of particular importance.
The following objectives are to be achieved as a matter of priority:
- Reducing heat stress and increasing cooling capacity on hot summer days and improving the quality of stay
- Cooling buildings in hot weather and increasing insulation in winter
- Improving air quality by binding dust and pollutants Creating new habitats for flora and fauna (urban stepping stone biotopes)
- Relief for municipal drainage facilities through rainwater retention
- Increasing the attractiveness of the residential environment, increasing the value of the property and enhancing the cityscape
On 12.07.2017, the urban green and design statutes were adopted by the Aachen City Council. It must be applied to all building projects and new constructions.
In addition, a municipal funding program for green roofs and façades is now to be established. It is aimed at land and building owners of existing private and commercial properties.
Roof greening
Green roofs store rainwater - up to 80 percent - and slowly evaporate it again. This relieves the burden on sewage treatment plants and ensures a more balanced urban climate. They produce oxygen, filter polluted air and absorb radiation. They have a temperature-equalizing effect as thermal insulation, dampen noise and protect the roof from the effects of weather and minimize mechanical wear. They are financially worthwhile for detached houses, but also for industrial and administrative buildings and large halls. The performance of air conditioning systems can be significantly reduced.
Suitability of the roof
The suitability of a roof for a roof foundation is limited in particular by the factors of roof pitch and statics.
Flat roofs offer ideal conditions for a green roof. For roofs with a maximum pitch of 10°, the owner has a free choice between intensive and extensive greening. The greater the pitch of a roof, the more complex the construction becomes, as measures for shear protection must be planned. Depending on the thickness of the structure and the vegetation selected, extensive green roofs can support weights of up to 170 kg/m² when saturated with water, while intensive green roofs can support static loads of between 200 and 500 kg/m².
As a rule, extensive green roofs achieve construction heights of 8 to 15 cm, extensive roofs between 15 and 80 cm
In any case, it is important to check to what extent the desired roof is able to bear the weight of the greenery. It is best to consult a professional for the necessary structural assessment.
Guidelines and standards
If you have the work carried out by a specialist company, they will also take care of all legal and safety issues. If you want to install the green roof yourself, make sure that your green roof does not become a safety risk. Information on the correct installation of a green roof can be found in the FLL green roof guidelines and the DIN standards mentioned there.
Greening
Extensive green roofs
Robust, low-growing, perennial and hardy plants are used, which are adapted to the extreme conditions and form a closed vegetation cover without requiring much maintenance. They have a layer structure of 8-15 cm, are not actively used, are not watered and are only walked on as part of maintenance work. With the installation of shear protection, greening is possible on pitched roofs up to max. 45°.Intensive green roofs
A "roof garden" is created using perennial shrubs (of any size), woody plants and small to medium-height trees. This is characterized by higher demands on water and nutrient supply, a build-up thickness of 25 cm to 1 m and loads of up to 1,200 kg/m³ as well as a complex structure. The roof pitch is max. 5°, irrigation must be possible and the maintenance requirements are the same as for a garden.
Facade greening
Green façades contribute to the ecological and aesthetic enhancement of the cityscape by insulating and storing heat and by increasing the natural diversity of species (birds and insects). Numerous bird and insect species find a habitat, breeding ground and feeding ground here.
Temperature fluctuations of green façades are lower (in summer heating to a maximum of 30 degrees, in winter less cooling). The leaves in summer and tendrils in winter form an insulating air cushion, reducing heat loss to the inside and outside. This also results in economic advantages.
Concerns that the façade will be damaged by climbing plants "taking root" are unfounded, as the plants (self-climbers) do not grow "in" the walls, but "cling" to the surface of the façade with suction cups, adhesive discs, climbing hairs or adhesive roots.
In principle, any building can be greened (monument protection requirements must be observed) and greening can also be started on buildings that have not yet dried out, as the slow growth of the plants means that success often only becomes apparent after three to four years.
Plant selection
A distinction is made between ground and wall-mounted greening techniques and between "self-climbers" and "climbing plants" based on their climbing characteristics. The latter require a climbing aid (trellis or ropes).
Depending on the wall orientation, light availability and water balance, various species (including winter greens) are suitable.
Fears of mould or wall damage are unfounded. On the contrary, the base of the wall is kept dry by the continuous water extraction of the roots.
Every façade greening requires maintenance, which usually takes the form of pruning once a year (more often if necessary).Constructive decision parameters
Ground-based greening
Self-climbers (root climbers or adhesive disk climbers) are suitable, as are climbing and creeping plants (spreading climbers or trellis plants) that require climbing or climbing aids (rods, ropes, trellises or nets). Single-shell solid wall constructions made of stone, wood or metal are suitable. Curtain-type, rear-ventilated composite thermal insulation façades are only suitable to a limited extent.
Wall-mounted greenery
A distinction is made here between planters on supporting structures (also suitable for curtain-type, rear-ventilated façades and composite thermal insulation systems) and modular or flat structures and systems that are suitable for solid structures made of wood, stone or metal. Perennials, grasses and ferns are used in containers (baskets/gabbions, mats or cassettes).
Special form of solar roof
The amendment to the building regulations, according to which a PV system will be required for new buildings from 2025 and for roof renovations of old buildings from 2026, does not rule out the creation of green roofs.
The combination of solar thermal energy or photovoltaic modules with a green roof makes economic and ecological sense. Appropriate elevations must be used to ensure that there is no interference between the solar system and the green roof (shading) and vice versa (raised frame at a distance from the vegetation).
The power loss of semiconductors in PV modules is minimized by the green roof as the temperature on green roofs rises less due to evaporation effects.
It should be noted that the combination entails an increased load for the roof.
A bonus is granted for the use of this special form as part of the funding.
Promotion, process and procedure
Promotion
On 14.06.2022, the Committee for Climate and Environment of the City of Aachen adopted a program to promote green roofs and façades. The funding supports private and commercial applicants with properties in Aachen. It is also possible for housing associations or tenants to receive funding with the consent of their owner.
The funding amount for the individual areas and all other framework conditions can be found in the "Guidelines of the City of Aachen for the promotion of green roofs and facades from 01.07.2022".
Application procedure
If you have any problems with the application via the service portal of the City of Aachen, please contact us by email: umwelt@mail.aachen.de. We will then find an alternative way for you to submit your application.
For registered monuments, approval and permission from the lower monument authority is required.Procedure
Once the complete application has been submitted and processed, you will receive a grant notification from the responsible department of the City of Aachen and can then begin with the measure. After completion of the measure, you will indicate that it has been completed and, after reviewing the receipts, you will receive the requested funding (possibly with deductions if parts have not been implemented as requested).
Procedure
In principle, own work is also eligible for funding under certain conditions. When installing green roofs in existing buildings, it is advisable to seek advice to clarify the statics.
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Contact us
Climate and Environment Division
Tel.: 0241 432-36222
Mail: gruensatzung@mail.aachen.de or umwelt@mail.aachen.de