Extensive green roofs are lightweight with a shallow layer of growing substrate of less than 200 mm deep, requiring minimal maintenance. They generally have lower water requirements and use small, low-growing plant species, particularly succulents. ‘Ecoroofs’ or ‘brown roofs’ are terms used to describe these extensive green roofs. Roofs that are designed and planted specifically to increase local plant diversity and provide habitat (food and shelter) for wildlife are known as ‘biodiverse green roofs’.
Intensive green roofs are generally heavier, with a deeper layer of growing substrate, and support a wider variety of plant types. Because they can support a heavier weight, they are readily accessed by people. Intensive green roofs need more irrigation and maintenance than extensive roofs, and are highly engineered landscapes, often built directly on structures with considerable weight load capacity, such as car parks. ‘Roof gardens’ or ‘podium roofs’ are terms also used to describe these types of green roofs. Rooftop gardens are used particularly for sites where less space is dedicated to the vegetation and growing substrate and more to hard infrastructure such as decking.
Until quite recently, extensive green roofs were usually designed as lightweight installations that were not publicly accessible, while intensive green roofs were designed as amenity spaces for people. The boundaries between these types of roofs are now less distinct, and terms such as ‘semi-intensive’ or ‘semi-extensive’ are used to describe roofs that show elements of these major categories. Each green roof is unique and may incorporate a mix of design elements; strict classification of types is no longer as helpful or relevant as it once was. Around the world, designers and their clients, and those who install and maintain green roofs, are exploring a range of creative solutions.
- Excerpts from Growing Green Guide