Living Roofs: What are Intensive & Extensive Green Roofs?
As we begin to adopt new technologies to green up our urban spaces, planners and designers are opening to the idea of greening up more roof spaces. Whether it is the unused flat roof on top of a multi-storey carpark, or the bare rooftop of an old skyscraper, the untapped potential in these “wasted” spaces are arguably ripe for the picking. Therein lies the opportunity to convert these spaces into green roofs, whether intensive or extensive.
When it comes to green roofing, the abovementioned terms intensive & extensive are often bandied about. But how many of us are really able to distinguish between the two kinds of green roofs? In this post, we shall attempt to lay these doubts to rest – here’s a brief comparison between intensive green roofing & extensive roofs. (TLDR; scroll down to the last image)
INTENSIVE GREEN ROOFS are described in the Guidelines for the Planning, Execution and Upkeep of Green Roofs (published by the German Landscape Research, Development and Construction Society, or FLL for short) as “…the planting of shrubs and coppices, as well as grassed areas, even an occasional tree.” and it also mentions that “Regular attention is needed to maintain sites of this type in good order, in particular regular watering and feeding is required“. In simple terms, intensive green roofs allow for the widest range of plants and shrubs to be planted on the roof area, restricted only by the property’s design intent and structural constraints. The inclusion of grasses that are trafficable also allows users to step onto these green roofs for leisure activities such as picnics or strolls.
That said, the substrate needed to sustain these plants are usually deeper, which translates into a massive weight addition to the building’s structure. Deeper growing medium also means that planters have to be specifically created to suit the location of these plants. Lastly, an intensive design is usually accompanied by a high up-front cost (taking into consideration the structural load and creation of planters) as well as incur more substantial maintenance efforts to ensure a thriving green roof.
EXTENSIVE GREEN ROOFS on the other hand, are limited by their thin built-up and inherent system traits to provide a shorter list of species. The reason for this being that extensive green roofs advocates the lowest form of maintenance, hence the usage of hardy local species that require close to zero attention upon installation. This also means that these roofs are usually located in areas to which the public have limited to no access.
The FLL in Germany classifies extensive green roofs as “… cultivation of vegetation in forms which create a ‘virtual Nature’ landscape and requires hardly any external input for either maintenance or propagation”. Being inaccessible and catering to a narrower range of species for this kind of green roof are tradeoffs to the following attributes:
- Lowest form of maintenance due to hardy local plants
- Lightweight (As reference, the GaiaMat extensive green roof is 6 times lighter than convensional roof turfing systems)
- Lower up-front cost
- Able to retrofit different roof types- RC flat roof, Metal decks and even glass roofs.
To sum it all up, here’s a table comparing both roofing systems, extracted from the Green Roof and Wall Policy in North America – Regulations, Incentives and Best Practices (2019):
We hope this helps to clarify any doubts on what we call Extensive and Intensive green roofing! For enquiries on using our GaiaMat (extensive) or the GaiaTurf (intensive) green roof system, please do drop us a message in the contact form (<< click here).