Why Build Green Roofs & Rooftop Gardens 

Rooftop gardens and green roofs are similar techniques that provide an opportunity to take “wasted” space and transition them into plant-filled areas. This type of design grows vegetation directly on a roof over a waterproof membrane. Green roofs and rooftop gardens are at times designed to completely cover the roof space, while at other times, are designed to partially cover roof areas so that there is space for humans to walk through or engage with the space. 

rooftop garden

Designing green roofs

Green roof and rooftop garden designs will vary based on climate, region, building, and roof type. Therefore, when designing a green roof, there are many factors to take into consideration such as the slope of the roof, any existing material on the roof, the structure’s load capacity, drainage systems, waterproofing, and adequate supply of water and electricity.  In order to make sure that green roof systems can provide waterproofing, it is important to build green roofs in several layers. Green roofs typically include six to seven layers, with the bottom layer consisting of a waterproof membrane, on top of which lies a root repellent system, a layer of insulation, a layer of drainage, a cloth to filter finer soil, a soil substrate, and at the top, the vegetation. 

rooftop drainage

There are two general types of green roofs, extensive green roofs and intensive green roofs. Extensive green roofs are a more self-sustaining option that require little maintenance, irrigation, and fertilization, and usually are designed on existing roof structures. For this type of design, roofs with slopes of 33% are best. These spaces are landscaped with self-seeding sedums, mosses, succulents, and grasses that are typically drought-tolerant. Extensive green roof designs are not typically designed for human-use or recreational purposes, but merely for ecological landscapes.

Extensive Green Roof

Intensive green roofs, in contrast, are more labor-intensive and often require engineering needs prior to designing the green roof. Intensive green roofs are best on flat roofs or low-slope roofs that at most have around a 3% slope. Intensive green roofs require more soil since these designs are typically used to grow and sustain larger plants, like shrubs and small trees, or lawns. These designs are intended for humans to interact, and often include water features like fountains and walking paths. Intensive rooftop gardens therefore act as parks.  

London Intensive Green Roof

Benefits of rooftop gardens & green roofs

Rooftop gardens are essential in integrating plants and vegetation with buildings while providing several benefits to the environment, society, and economy. For example, green roofs reduce the impacts of stormwater runoff plus decrease the volume of stormwater runoff as they are able to absorb rainwater. Green roofs are vital during wintertime by providing insulation to buildings, preventing heat loss, and reducing energy consumption. In urban areas during warmer seasons, green roofs mitigate the urban-heat island effect, which is when an urban or metropolitan area is significantly hotter than surrounding areas, often due to anthropogenic activities. This allows green roofs to lower urban air temperatures and decrease energy needs for air conditioning. Green roofs and garden rooftop designs can also improve ventilation and air quality, provide increased sound insulation, and even increase the lifespan of a roof. By effectively designing and implementing green roofs and rooftop gardens, there are so many benefits that humans and the environment can experience. 

Read our post on Plants in New Places to learn about some sustainable places to visit with green roofs and rooftop gardens!

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