Green roofs: A contribution to sustainable urban development

Green roofs are becoming increasingly important in urban areas as they not only help to beautify buildings, but also offer numerous ecological and economic advantages. Cities such as Copenhagen, London and Hamburg are pioneers in promoting and implementing green roofs through legal regulations, incentives and funding programs. In Copenhagen, green roofs are required for most new buildings. This development is part of the climatic restructuring of inner cities to make urban spaces more resilient to the effects of climate change and to reduce so-called “heat hotspots” caused by the reflection from buildings.

The advantages of green roofs

The benefits of green roofs are diverse and range from ecological to economic advantages.

Ecological benefits: Green roofs create new habitat for plants and animals in urban areas that are otherwise often dominated by concrete and asphalt. They help improve the urban climate by improving air quality by filtering dust and pollutants and cooling the ambient temperature through evaporation. Especially in cities with a high density of sealed surfaces, green roofs act like green islands that have a positive effect on the microclimate.

Improvement of sound insulation: Green roofs absorb sound and thus reduce the noise level both in the building and in the surrounding area. This is particularly beneficial in urban areas where noise pollution is a major problem.

Energy saving: In addition, green roofs improve the energy balance of a building. The vegetation acts as additional thermal insulation, keeping the heat out in summer and storing heat in the building in winter. This leads to lower energy consumption and therefore lower heating and cooling costs.

Extending the lifespan of roofs: Another important aspect is extending the lifespan of a roof. The vegetation protects the roof from external influences such as UV radiation and extreme temperatures. This reduces wear and significantly extends the lifespan of the roof structure.

Types of green roofs

There are different types of green roofs, which are differentiated depending on requirements and intended use. Each species has specific ecological functions that contribute to improving the urban ecosystem:

1. Extensive greenery: These are easy to care for and cost-effective as they require a thinner substrate layer (approx. 3-8 cm) and less intensive care. Extensive green roofs are ideal for roofs that are rarely or rarely walked on, and they are particularly suitable for low-growing, robust plants that can survive even in extreme conditions. They make a significant contribution to biodiversity by creating new habitats for specialized plant and insect species.
2. Simple intensive greening: This form of greening requires a medium substrate layer and offers more design options than extensive greening. It can include a wider variety of plants, including shrubs and smaller woody plants, and requires more regular care.
3. Intensive greening: This type of greening is similar to a conventional garden with a variety of plants, including larger trees and even small trees. It requires a thicker substrate layer (more than 20 cm) and intensive care, including watering, fertilization and regular maintenance work. These green spaces offer a particularly high aesthetic quality and at the same time make a significant contribution to air pollution and to reducing urban heat islands.

Requirements for plants and substrates

Choosing the right plants and substrates is crucial for a successful green roof. These trees and plants must also meet the strict requirements of DIN 18916 and the FLL quality regulations for nursery plants. Particularly when it comes to green roofs, if the substrate coverage is low, plants with shallow root systems that are free of foreign vegetation should be chosen. Rhizoma-forming plants should be avoided on roofs as they can damage the roofing material.

There are also special requirements for the substrates. They must be light, stable and retain water well in order to provide plants with optimal growth conditions even under extreme conditions. In practice, specially developed substrates are often used that meet these requirements and at the same time do not increase the weight of the roof structure.

Implementation and practical examples

The implementation of a green roof requires careful and early planning and execution. Particularly in the case of intensive greening with larger trees, special measures are required to anchor the plants so that they remain securely on the roof even in strong winds or extreme weather conditions. There are various techniques for this, such as static anchoring with retaining ropes or special bale bracing.

Examples of successful green roofs can be found in many cities around the world. The “House of Trees” project in Vietnam has shown that it is even possible to plant trees on roofs and use them as water storage at the same time. In cities such as Berlin, Milan and Vienna, large construction projects such as Charlie Living, the Dachpark in Darwinstrasse, the Erste Campus Wien and the Bosco Verticale have shown how effective and versatile green roofs can be implemented.

Conclusion

Green roofs not only offer ecological and economic advantages, but also contribute to the creation of livable and environmentally friendly urban spaces. With early planning before construction and correct execution, almost any roof can be transformed into a green oasis that sustainably improves life in the city. It is crucial to include the statics of the building in the planning from the outset to ensure that the roof can bear the additional load of the greenery.

Recommendation list for green roofs

This list represents a recommendation for the selection of trees and plants for green roofs. The actual selection of plants depends on various factors, including:

• Site conditions: These include climatic conditions such as temperature, wind conditions, solar radiation and the height of the building. These conditions affect the resilience of plants and their ability to thrive in an urban environment.
• Substrate Thickness and Composition: The thickness and type of substrate used on the roof plays an essential role in plant selection. Shallow-rooted plants are particularly suitable for roofs with a thin substrate, while deep-rooted species require a thicker substrate layer.
• Care effort: The planned care effort influences the choice of plants. Extensive greenery requires less care than intensive greenery, which requires regular watering, fertilization and pruning.
• Roof weight limit: The load-bearing capacity of the roof is a critical factor. Some plants and substrates can be very heavy, which may require additional structural support.
• Aesthetic goals: The desired visual effects also play a role. For example, larger trees can provide structure and shade, while ground-covering plants and shrubs contribute more to greening areas.
• Ecological functions: Promoting biodiversity, creating habitats for birds and insects, and improving microclimate are also important considerations.
• Legal requirements: Local building regulations and environmental laws may limit the selection of plants or have special requirements for green roofs.
• Climatic conditions: These include extreme temperatures (hot and cold), sensitivity to frost, strong winds and the cold of winter. These factors determine which plant species are resilient enough to survive on a roof.
• Type of building: The use and construction of the building, such as residential, commercial or industrial buildings, influences the design of the green roof.

It is important to include all of these factors in the planning to ensure a long-lasting and functional green roof. Thorough advice from experts and detailed planning are therefore essential.

1. Laubbäume und Großsträucher

Diese Kategorie umfasst größere Gehölze, die für intensive Dachbegrünungen geeignet sind. Sie bieten eine ausgeprägte Struktur und können als dominante Elemente in der Dachgestaltung dienen.

2. Medium to small shrubs

Medium-high and small shrubs are ideal for adding structure and color to green roofs without taking up too much space.

3. Small and dwarf shrubs, ground cover

These plants are ideal for extensive greenery and are particularly suitable for roof areas with less substrate.

4. Climbing trees

Climbing plants can add greenery to walls and other vertical structures and are ideal for adding additional dimensions to green roofs.

5. Conifers

Coniferous trees bring evergreen structures to green roofs and are a highlight, especially in winter.