The Complete Guide To Green Roofs and Their Benefits

Green roofs can be partially or entirely covered with plants and vegetation, creating a lush, living roof environment. Additionally, the installation of green roofs can increase the lifespan of the existing roof by protecting it from UV damage and thermal movement. In this guide, you’ll learn what green roofs are and the benefits they provide.

Green roofs are crucial in transforming urban environments and benefit building owners. Unlike simple rooftop gardens, these specially designed systems support plant life and protect buildings from harsh weather.

The benefits of green roofs extend far beyond aesthetics. They offer solutions to urban heat islands, energy efficiency challenges, stormwater management in sustainable cities, and health benefits such as improved air quality and positive public health outcomes.

A green roof system has multiple layers to support plant growth while protecting the underlying roof structure. Also known as living roofs or vegetated roofs, these systems include essential components: a waterproof membrane, root barrier, drainage layer, filter layer, growing medium, and carefully selected vegetation.

Green roof technology differs significantly from container plantings or simple roof gardens. The waterproofing layer is the foundation, while the root barrier prevents plant roots from penetrating and damaging the roofing material. The drainage layer ensures proper water management, and the soil substrate provides nutrients for vegetation growth.

When designing a green roof, the components required will depend on the type of vegetation specified and how the balance between water retention and drainage is achieved to meet the demands of the vegetation. The general principle is to recreate the conditions nature provides in a shallower system. In all green roof scenarios, substrate depths are completely dependent on the vegetation specified and the different drainage / water retention layers are selected according to the levels of water required to be held within the construction. 

Extensive green roofs are lightweight, featuring shallow soil depths. They support low-maintenance vegetation like mosses, sedums, and grasses, making them ideal for buildings with limited load-bearing capacity. Plus, they require minimal maintenance. When wildflowers are used, you would then be looking at the higher end of the depth.

Typical Extensive Vegetation depth is 60mm to 120mm. 

Semi-intensive green roofs combine elements of both extensive and intensive green roofs, with moderate soil depths and a mix of plant types. They provide a balance between weight, maintenance, and biodiversity. Irrigation on these roofs depends on the plant life, and may be needed depending on the time of year. It can be done by watering for a few weeks and allowing it to soak completely.

Semi-intensive’s typical depth is from 80mm to 150mm. A minimum of 80mm for BROOFT4.  

Intensive green roofs resemble traditional gardens, featuring deeper soil layers that can reach up to several feet. This allows them to support a diverse range of plants, including shrubs and trees. While they require robust structural support and ongoing maintenance, they provide significant aesthetic and recreational benefits.

We suggest installing an irrigation system in these roof types, due to the type of plant life on the roof, which is generally expensive and requires proper care. Substrates above 200mm will become intensive in general.

Green roof systems are closely linked to urban sustainability because they help with urban heat island problems, stormwater management, and building energy efficiency. Each green roof helps cool down cities differently, improves air quality, and makes buildings use energy more efficiently. They can also make cities quieter by blocking outside noise.

Green roofs offer significant environmental benefits that address critical urban challenges. These living roof systems can make the air around them up to 11°C cooler, helping to fight the urban heat island effect that makes cities hotter. They also lower the surface temperature and absorb less heat from the sun, which keeps buildings cooler and helps them use energy more efficiently.

Energy savings represent a significant advantage, with green roofs delivering 70% cooling load reduction and 15°C indoor temperature decrease compared to conventional roofs. Green roofs can also significantly reduce energy consumption and cooling loads compared to traditional roofs. This dramatic temperature reduction translates to substantial annual energy savings by reducing air conditioning demands during peak summer months.

Other key benefits include: 

• Improvement of commercial and residential environments - Roof greening is a component of sustainable building. Accessible roofs can serve as additional living spaces, playgrounds, sports areas and communal meeting points.

• Pollution filtered, CO2 absorption - Particle matter and air pollutants are filtered out – they are bound in the substrate, decomposed and absorbed by the plants. CO2 is also reduced.

• Replacement of lost habitats - Green roofs provide temporary and permanent habitats for vegetation and animals. They offer resting, feeding and nesting opportunities.

• Attract new wildlife - Biodiverse roofs will support the growth of existing plants and attract insects and animals.

• Rainwater Retention - Green roofs offer valuable rainwater retention benefits, with performance varying by roof type. Extensive sedum roofs typically retain 50–60% of rainfall and provide around 35 L/m² of permanent water storage. Semi-intensive biodiverse systems improve this to 60–70% retention and roughly 50 L/m² of storage. For the highest performance, intensive green roofs can retain 70–95% of rainfall and store approximately 160 L/m², significantly reducing stormwater runoff and easing pressure on drainage networks.

• Improvement of the local microclimate through evaporation and transpiration - The retained rainwater evaporates and cools the surrounding area.

• Minimisation of rainfall runoff peaks - Incidents caused by heavy rains are reduced by 50 - 100 % and water discharge to the sewer system is delayed.

• Improvement of sound insulation - through greater vibration control of the roof surface and good sound absorption by the vegetation. The mass of the green roof construction and the structure of the vegetation contribute to noise reduction in large cities and areas crossed by airport flight paths.

• Enhancement of roof insulation - The green roof construction functions like an additional insulation layer: in the summer it serves as a heat sink, in the winter as thermal insulation.

What are the main benefits of green roofs?

Green roofs reduce cooling loads by up to 70%, lower surface and indoor temperatures, improve air quality by filtering pollutants, support biodiversity, and retain 40–60% of rainfall runoff to reduce flooding. They also help buildings last longer and make cities greener and more pleasant.

How do green roofs help with urban heat islands?

Green roofs reduce urban temperatures and surface heat by providing vegetation cover and evapotranspiration, mitigating the urban heat island effect. They also cool down surrounding areas, making cities more comfortable during hot summer months.

Can green roofs improve air quality?

Green roofs filter air pollutants such as nitrogen, sulphur, and particulate matter, improving air quality in urban areas. They also release oxygen and trap dust, which helps create cleaner, healthier air.

Do green roofs support wildlife?

Green roofs create habitats and corridors for urban wildlife, promoting city biodiversity. They give birds, insects, and pollinators safe places to live and travel through urban spaces.

Understanding the different types of green roofs helps property owners select the right system to maximise these benefits. Extensive green roofs offer low maintenance and cooling benefits, semi-intensive roofs provide moderate plant diversity, and intensive roofs create full roof gardens with recreational opportunities.

By incorporating green roofs, urban areas can become more sustainable, healthier and more comfortable places to live and work. If you want to integrate green roofs in your roofing system, talk to one of our expert teams below.