Green roofs have many advantages. In addition to the visual enhancement of the area, in a densely built-up inner-city situation as well as in the open countryside, there are also many practical reasons that speak in favour of a green roof. This significantly extends the life expectancy of the waterproofing by mitigating the extreme climatic and environmental influences. Green roofs heat up less and out of phase in summer, which has a positive effect on the room temperature of the rooms below.
Image: System structure for extensive green roofing - bauwion
A green roof also makes a positive contribution in terms of sound insulation and shielding against electromagnetic radiation. Among the many advantages of a green roof, the higher costs for production (and especially for maintenance in the case of intensively green roofs) must also be taken into account. In any case, planning should be carried out taking into account and applying the Green Roof Directive. The application of the Directive is not generally prescribed, unless this results from project-specific laws, regulations or contracts, but it is strongly recommended in order to ensure that the green roof
is carried out properly.offunctional layers of a green roof: see encyclopedia article in the right-hand column.
Types of greening: A distinction is made between extensive and intensive greening. Extensive green roofs are light and have a low installation height. Plants with minimal care requirements such as sedum, wildflowers and wild herbs are sown. Intensive greening offers significantly more design options, but also with higher costs, higher weight per unit area and increased maintenance costs. The design options are similar to those of a garden, e.g. with lawns, water areas, woody plants and perennials. The Green Roof Directive also lists the third category "Simple Intensive Greening", which represents a kind of "intensive greening light" with a limited selection of plants and reduced layer structure.
Use of green roof areas: In principle, extensive and intensive green roof areas, with the exception of landscaped path and terrace areas, are not intended for use by persons, except for inspections for the care and maintenance of the areas. If further use is to be possible, the resulting differences to an unused roof, especially with regard to fall protection and static requirements (traffic loads), must be taken into account at an early stage in the planning. Especially in the case of the conversion of an existing roof area, the additional loads from the modified roof structure and additional traffic loads must be examined with regard to their feasibility.
Urban farming: Increasingly, users also want to use available green roof areas in large cities for agriculture by growing fruit (e.g. raspberries, blackberries, currants) and vegetables (e.g. lettuce, tomatoes, peppers, zucchini, cucumbers, beans), especially for their own use. In principle, this is possible in the case of an intensive green roof construction if the above-mentioned differences to an unused roof, in particular with regard to fall protection and static requirements (traffic loads), are taken into account.
Greening of pitched roofs: The greening of pitched roofs (roof pitch 5° - 45°) is also possible. In addition to the faster water drainage, the increased slip and shear stress of the superstructure must also be taken into account. If a flat shear protection system is not used for roof pitches below 15°, a static proof of the thrust absorption in the eaves is required. The increased water drainage can be compensated for by a modified structure with greater storage capacity, e.g. thicker water storage plates, . Possibilities for carrying out the necessary anti-slip and anti-slip systems, e.g. with mats, profiles or thresholds, are described in the Green Roof Directive under point 6.10 depending on the respective roof pitch and/or can be obtained from the respective manufacturer.
System: The compatibility and compatibility of the various component layers with each other must be checked. However, most manufacturers also offer tested systems for entire roof structures for the different requirements, so that there is certainty of layer compatibility for their planning. In the transition to the waterproofing underneath, it is recommended in most cases to install a separation layer in order to rule out chemical incompatibilities of the green roof structure with the waterproofing .
Roof construction/subsoil: The subsoil must be examined with regard to its suitability for a green roof structure, in particular:
Details depending on the respective construction method are described in the Green Roof Directive under points 5.4 - 5.6.
Fall protection: In accordance with the accident prevention regulations of the employers' liability insurance associations and accident insurers, fall protection must be provided both temporarily during the construction project (see BGV C22 or GUV-V C 22) and permanently for subsequent maintenance and care work (see BGI 5164).
Irrigation/drainage: For irrigation of the green areas, at least one frost-proof water connection must be provided on the roof surface. Details on the planning of drainage, including roof drains and emergency overflows, are described in the Green Roof Directive under point 5.8.
Edge strips: A vegetation-free safety strip must be arranged on rising components and facades, e.g. made of coarse gravel or pavement slabs. When determining the strip width, any other requirements must be taken into account, e.g. with regard to fire protection (see below) or use as a work surface for façade cleaning.
Fire protection: According to § 32 para. 1 of the Model Building Code (MBO), "roofing must be resistant to external fire exposure from flying fires and radiant heat for a sufficiently long time (hard roofing)". Para. 4 adds: "Deviating (...) (...) green roofs are permissible if there is no fear of fire arising from external fire exposure to flying fires and radiant heat, or if precautions are taken against this".
In June 1989, a working group of the ministers and senators of the federal states responsible for construction, housing and settlements (ARGEBAU) adopted the model decree "Fire behaviour of green roofs", which specified the conditions under which a green roof can be classified as hard roofing (abridged summary):
Regularly maintained and watered intensive greening with a correspondingly thick substrate layer is therefore generally to be classified as hard roofing.
Extensive greening is to be classified as hard roofing under the following conditions:
The model decree was adopted to varying degrees and with different modifications in the individual state building codes or their administrative regulations/implementation instructions/recommendations for action. The responsible planner of a construction project must therefore clarify, if necessary also in consultation with the responsible building supervisory authority, under what conditions a green roof can be classified as hard roofing in the respective federal state.
Selection of plants: When selecting plants, the respective site conditions must also be taken into account, the Green Roof Directive distinguishes between climatic/weather-related, building-specific and plant-specific factors. Details are described in the Green Roof Directive under point 3.3, further requirements for seeds, plants and vegetation under point 11.
Single-layer construction: A special case in green roof construction is the so-called single-layer construction method. Here, a homogeneous fill simultaneously takes over the functions of the drainage, filter and vegetation base layer. The single-layer construction method enables the greening of large areas with little time and cost. However, these advantages are offset by considerable disadvantages: due to the lack of a filter layer, the drainage effect decreases over time, the risk of waterlogging increases, there can be increased moss formation and also a significant increase in the original roof load, which must therefore be designed correspondingly higher in relation to the supporting structure from the outset. The lack of layer separation also makes it harder for water and nutrients to be stored, resulting in an increased need for irrigation and fertilization. The initial cost and time savings compared to the conventional multi-layer green roof structure are thus offset by increased maintenance costs.
measures in accordance with DIN 18195: Protective measures serve to temporarily protect the waterproofing during further construction measures and must be adapted to the type and duration of the construction measures until the final protective layer is created. Chemical substances that can damage the waterproofing must also be taken into account, e.g. lubricants, solvents or formwork oil. No loads may be placed on unprotected waterproofing and the surfaces must only be entered with suitable footwear and if absolutely necessary.
Greening: Depending on the form of vegetation, plant species and greening goal, greening is carried out by dry sowing, wet seeding, scattering of sprouts, planting of individual plants or covering of pre-cultivated vegetation mats or finished lawns, combinations of several methods are also possible in principle.
Erosion control: Suitable measures must be taken to ensure that the green roof structure, which is still unconsolidated after installation, is not damaged by wind and water. Depending on the structure, wind exposure and roof pitch, this can be done, for example, by keeping the vegetation substrate constantly moist, or by using an erosion control fabric, wet sowing or covering pre-cultivated vegetation mats. Details on this are described in the Green Roof Directive under point 14.
Completion maintenance: Depending on the type of vegetation, various measures are required for completion maintenance. These are described in DIN 18916 and DIN 18917 for extensive greening and can be transferred accordingly to intensive greening. The measures include, for example, irrigation, fertilization, pest control and reseeding.
DIN 18195, Parts 3, 5, 8-10, Building Waterproofing
DIN 18234, Structural Fire Protection of Large Roofs, Fire Exposure from Below
DIN 18531, Part 1-4, Roof Waterproofing
DIN 18916, Vegetation Technology in Landscaping - Plants and Planting Work
DIN 18917,Vegetation Technology in Landscaping - Lawn and Sowing Work
DIN 18918, Vegetation Technology in Landscaping - Engineering Biological Safeguarding Methods - Safeguarding by Sowing, Planting, Construction Methods with Living and Non-Living Substances and Components, Combined Construction Methods
► BGV C22 Accident Prevention Regulations Construction work, of 1 April 1977, in the version of 1 January 1997, Publisher: HVBG Hauptverband der gewerblichen Berufsgenossenschaften
Flachdachrichtlinie, Fachregel für Abdichtungen, Ausgabe Oktober 2008, letzte Änderung Dezember 2011: Rule for waterproofing of unused roofs, Rule for waterproofing of used roofs and areas
Roof Greening Directive, guideline for the planning, execution and maintenance of green roofs. Edition 2008, Hrsg.: Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau e. V. (FLL), Bonn.
Source: bauwion
