How to Choose the Right Plants for a Live Green Roof to Increase Insulation?

April 4, 2024

Choosing the right plants for a live green roof is critical to maximize the insulation of a building. Traditionally, buildings have been constructed with flat or pitched roofs made of concrete, asphalt, or other non-porous materials. However, in recent years, the benefits of installing green roofs have become more apparent. These roofing systems don’t just mitigate heat loss but, more importantly, they contribute to biodiversity, reduce stormwater runoff, and improve air quality.

The choice of plants for your green roof depends on various factors like the type of green roof system, the climate, the depth of the substrate layer, and the maintenance required. In this guide, you’ll learn about the two major types of green roof systems, the selection of appropriate plant species, and the crucial role of the substrate and drainage layers.

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Understanding Extensive and Intensive Green Roofs

Before selecting plants for your green roof, you need to understand the difference between extensive and intensive green roof systems.

Extensive green roofs are low-profile, low-maintenance systems designed to be self-sustaining. They typically have a shallow soil layer, ranging from 2 to 6 inches in depth. Due to their light weight, extensive green roofs are suitable for most buildings without requiring additional structural support. They are typically vegetated with drought-tolerant plant species, such as sedum, that require minimal maintenance.

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On the other hand, intensive green roofs mimic traditional gardens with a thicker substrate layer, usually over 12 inches. This thickness allows for a greater variety of plant species, including shrubs and small trees. However, intensive green roofs are heavier and require more structural support. They also need more maintenance, including regular watering and fertilization.

Selecting Suitable Green Roof Plants

Plants play a crucial role in the performance of green roofs. They not only increase the aesthetic value but also improve the insulation properties of the roof.

For extensive green roofs, the common choice of plants are succulents such as sedum. Sedum is a low-growing, drought-tolerant plant that requires little maintenance. It comes in various colors and textures, adding visual appeal to the roof. Sedum is also excellent at storing water in its leaves, an essential characteristic for a green roof plant.

For intensive green roofs, you have a wider choice of plants. However, regardless of the type of roof, your chosen plants will need to withstand wind exposure, high temperatures, variable water availability, and limited nutrient supply.

Some suitable plants for intensive green roofs include perennial flowers, grasses, herbs, shrubs, and even small trees. It’s crucial to ensure that the plants you choose are compatible with your local climate. Your plant selection should also consider the biodiversity of your local ecosystem to support native wildlife.

The Importance of Substrate and Drainage Layer

The substrate and drainage layer are integral parts of a green roof system, providing the necessary medium for plant growth and managing excess water.

The substrate provides the root zone for the plants. A green roof substrate isn’t ordinary garden soil but a specially formulated mix that is lightweight, drains well, and retains water. It should also provide the necessary nutrients for plant growth.

The drainage layer is crucial for managing excess water. It prevents the substrate from becoming waterlogged, which could harm the plants and damage the roof structure. A well-designed drainage layer will retain some water for plant use while allowing excess water to drain away.

The depth of the substrate layer and the efficiency of the drainage system will largely determine the type of plants you can grow on your green roof.

Maintenance Requirements of a Green Roof

Maintaining a green roof is paramount to ensure it functions well and lasts for a long time. Generally, extensive green roofs require less maintenance than intensive ones. However, all green roofs require some degree of care.

Routine maintenance includes weeding, pruning, fertilizing, and watering. Weeding is necessary to prevent unwanted plants from invading the roof. Pruning keeps the plants healthy and aesthetically pleasing. Fertilizing replenishes the nutrients in the substrate, ensuring the plants grow well. Watering is particularly crucial in dry periods, although some plants, like sedum, can withstand prolonged dry spells.

Remember that maintenance requirements will also be determined by your choice of plants. Some plants may require more care than others, so consider the time and effort you’re willing to commit to maintaining your green roof.

Incorporating Solar Panels for a Green Roof

Incorporating solar panels into your green roof design can significantly enhance its performance. Green roofs and solar panels are an excellent combination, as they complement each other’s functions, leading to an optimally efficient and sustainable system.

Solar panels on a green roof can contribute to energy production, reducing the building’s reliance on grid electricity. The plants on the green roof can help cool the air around the solar panels, improving their efficiency. Meanwhile, the solar panels provide shade for the plants, reducing evapotranspiration and helping the plants retain water.

Furthermore, the combination of a green roof and solar panels can contribute to stormwater management. The plants and growing medium on the green roof absorb and slow the flow of rainwater, reducing runoff. The solar panels, meanwhile, divert rainwater to areas of the roof where it’s most needed, enhancing the irrigation system.

However, the installation of solar panels on a green roof requires careful planning. The structure of the roof must be able to support the additional weight of the panels. The arrangement of the panels should not obstruct the growth of the plants or limit their exposure to sunlight.

Green Roofs and Air Quality in Urban Areas

Green roofs can significantly improve air quality in urban areas. Plants on green roofs absorb carbon dioxide and release oxygen through photosynthesis, reducing the concentration of greenhouse gases in the atmosphere. They also filter out particulate matter and other pollutants from the air, contributing to cleaner, healthier urban environments.

Certain plant species are particularly effective at air purification. For instance, stonecrop sedum, a common plant for extensive green roofs, is known for its ability to absorb pollutants and heavy metals from the air.

Despite their benefits, it’s essential to remember that green roofs alone cannot solve the air quality problems in urban areas. They should be part of a comprehensive approach to urban greening, which may also include tree planting, the creation of green spaces, and the promotion of sustainable transport.

Conclusion

Choosing the right plants for a living roof is a complex process, but with careful consideration of the factors discussed above, you can successfully increase the insulation of your building, contribute to biodiversity, improve air quality, and manage stormwater effectively. Whether you opt for an extensive or intensive roof system, make sure to select plant species that are suitable for your local climate and can thrive with the available nutrients and water.

Maintenance, though different for each system, cannot be overlooked. Regular weeding, pruning, fertilizing, and watering will ensure the longevity and health of your green roof plants. Incorporating solar panels could also enhance the functionality of your green roof, leading to energy production and efficient stormwater management.

Ultimately, green roofs are an excellent investment for urban areas. They not only offer environmental benefits but also aesthetic value, potentially increasing the value of your property. So, when planning your green roof, consider your choices carefully to ensure you reap the full range of benefits that these systems can offer.