A roof garden is any roof that is partially or completely covered with vegetation.
Apart from the decorative benefit, a roof garden serves the purpose of providing architectural enhancement, temperature control, recreational opportunities, habitats for wildlife and food.
There are 2 types of roof gardens:
Extensive roof gardens
These have a very thin soil profile of between 140mm – 200mm making them much lighter to reduce structural support costs. The soils are specialised mineral-based soils designed to be long lasting with minimal degradation over time. The plants range from ground covers up to small shrubs and all require irrigation for establishment and sustaining over dry periods. Extensive green roofs are usually non-trafficable and only accessed for maintenance visits. Extensive roof gardens are often supported by a lightweight structure making them much less expensive to build.
Intensive roof gardens
These have a deeper soil profile of 200mm up to 1-2m depending on structural load-bearing capabilities and what is to be accommodated in the plant pallet. These look like parks on the roof and are made out of concrete bases and are trafficable hence require fall protection as part of the design. The vegetation in an intensive roof garden is similar to a backyard garden with flowers, shrubs, and trees. Many buildings are not suited to an intensive roof garden due to the size, weight, and scale as well as the demands on irrigation and maintenance.
In addition, a semi-intensive roof garden offers a combination where a slightly deeper soil layer is required than an extensive roof garden and that increases the diversity of the plant species that can be grown, without the need for a large, stable construction.
Designing a roof garden
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Once you understand the difference between an extensive and intensive roof garden then you can decide which type is required. It is much easier to develop a building’s design to support an extensive green roof as these are lightweight, easy to install and are typically created for environmental and aesthetic purposes.
Some of the benefits of an extensive roof garden include retarding and reducing stormwater runoff, reducing building temperature and power usage for cooling the interior, reducing the urban heat island effect by having less reflective heat, and the increasing opportunity for native fauna to survive in urban built-up areas.
An intensive roof garden, as we have already touched upon, usually consists of larger plants filled with a mix of evergreens, flowers, shrubs, grasses and trafficable turf. An intensive garden might also include outdoor furnishings and can often be considered as an outdoor ‘room’. You will typically find intensive roof gardens on flat surfaces due to the weight of the materials and the way the space will be used.
For planning and design purposes, all roof gardens will require planning permission and a waterproof membrane system specialised for roof gardens.
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In terms of the structure of the roof garden, the overall design will play a big part. For some roof garden designs, planter boxes can be used, however, a typical rooftop garden will require the following layers from the “host roof” up:
- Insulation – this may not be required
- Waterproof membrane – this is vital to ensure a membrane is suitable for roof gardens
- Drainage layer – to allow free flow of water to drain point
- Geofabric – to reduce the amount and prevent fines and roots penetrating to lower layers
- Growing media – mineral-based soils have a huge advantage of being long-lasting
- Plants and mulch layer – selection of these are crucial to be matched to the expected growing conditions.
The technical details that go into the makeup of each of these layers are all important in ensuring the long-term success of a roof garden.
Maintaining a roof garden
Once you have installed a roof garden, no matter the size or scale, some level of maintenance will be required. Often seen as a barrier to installation, maintenance can be kept to a minimum by working closely with your roof garden provider at the design phase to reduce the amount of manual maintenance required and manage much of the work via automation.
All commercial buildings with roof gardens are maintained by specialised roof garden maintenance teams and include checks like drain outlets, irrigation systems and all components that support the garden.
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Other maintenance tasks that are required include fertilizing, weeding, pest control and pruning.
Many small residential extensive roof gardens are maintained by the owner but SRS can provide this service usually on an annual maintenance contract.
Here at SRS, we work closely with our clients from day one to understand the desired outcomes of installing a roof garden, allowing us to gain a full understanding of not only the requirements, but also the expected amount of time clients can dedicate to maintenance, either conducted by themselves or an outside agency.
Benefits of rooftop gardens
The benefits of rooftop gardens are wide-ranging, from environmental, to cost-savings, to offering a place to carry out traditional gardening in urbanised areas. Here are some of the primary benefits of roof gardens:
- Expand outdoor living space
- Longevity of the roofing materials below
- Energy savings
- Converts CO? emissions
- Produces oxygen
- Creates a habitat for wildlife
- Reduces the ambient temperature
- Captures and harvest rainwater
- Reduces stormwater runoff
SRS group – helping bring your roof garden dream to fruition
If you are thinking about installing a green roof, talk to the team here at SRS Group. We have experts who have been working here in New Zealand and Australia, delivering gardens on building solutions to a variety of commercial and residential buildings.
Our enthusiasm for living foliage structures and roof garden spaces is two-pronged – it offers an edgy, on-trend yet soft design aesthetic, along with proven environmental benefits for both people and Mother Nature.
We combine a passion for creating impactful spaces through the use of foliage, with an unwavering commitment to sustainability.