Green roofing – not just a fancy lawn

Green roofs, a planting scheme established on a roof, structure or wall, can bring not only great aesthetic qualities to a building but a host of environmental, social and economic benefits as well. It’s also not just the reserve of large scale projects such as the Olympic Park that can benefit from installing green roofs, but the domestic house in the UK too, as the NFRC explains

So what about the benefits?
Green roofs can provide important refuge for wildlife and reduce surface run off, helping to minimise flash floods following intense periods of rainfall. They have been shown to reduce the need for air conditioning in the summer and offer a degree of additional insulation in the winter. The lives of waterproofing membranes beneath green roofs are extended, plus sound insulation and air quality are improved. Of course, in order to gain any of these benefits, and to continually do so, there are a number of factors that need to be borne in mind before a project begins.

Ask yourself what is it that you want from the green roof – is it for increased leisure space, encouraging more wildlife to the garden, or simply to do your bit for the environment? Whatever the reason is, there will be a suitable green roof.

Green roof types
There are in numerous types of green roof each with its own requirements and functions, though they can broadly be broken down into Intensive or Extensive systems:

  • Externsive
    A light-weight, low-maintenance roof system, typically with sedums or other hardy plant species planted into a substrate/ growing medium that is low in nutrients. Irrigation is not normally required once the green roof has established.
  • Semi-intensive
    Typically requiring a deeper level of substrate, a wider range of plants can be included such as shrubs and woody plants. Irrigation and maintenance requirements are dependent on the plants chosen.
  • Intensive
    Often referred to as a roof garden that provides similar benefits to a small park or domestic garden. Designed predominately for recreational use, intensive roofs often require a higher level of maintenance and irrigation.
  • Biodiverse
    Designed specifically to create a habitat that will attract a particular plant species, insects and birds by replicating their natural habitat. This type includes a brown roof, which is a low-vegetated version. The growing medium is purposely selected to allow plant species to inhabit the roof over time.

Specification
Once you have decided what it is that you want from your green roof, and the type of green roof it will be, it will be down to creating the right specification. With self-building, it would be worth speaking to your project manager or lead contractor to get advice. As with solar panels, anything where additional load is being placed on the roof structure needs to be checked prior to installation and, where necessary, strengthened.

Waterproofing
Waterproofing also needs to be looked at closely, whether its new build or refurbishment. This layer is by far the most important element of the roof; green roof or otherwise. It is this layer that ensures the integrity of the building. If you are looking to install a green roof on an existing roof, then it must be confirmed as being sound. Whilst a green roof can increase the life of the waterproofing it won’t be able to if there are underlying problems. If the layer needs to be replaced, or if it’s for a new build, it is advisable to speak to the supplier or the manufacturer to make certain that the product is suitable for green roofs.

Installation
Installing a green roof system is completely different to the installation of landscapes over natural ground. Ideally only people who have been trained in the installations of green roofs should undertake this task. However, if contractors who are untrained in green roof installation do attempt to install one, they should take particular care working at height and not to damage the waterproof membrane, among other considerations. There are increasing numbers of contractors who have received specialist training in green roof installation and care from organisations such as GRO (The Green Roof Organisation) and BALI (British Association of Landscape Industries).

Maintenance
As with the rest of your home, the maintenance of the green roof must not be overlooked. As with a garden, the green roof (depending on the type installed) will likely require irrigation, plant management and fertilising in order to prevent the living roof from dying or being overrun by weeds and so forth. The level and type of maintenance must be factored in during the design stages, as well as who will do it and what safe access will need to be provided.

There are other factors that need to be considered but an experienced installer will provide you with the support and guidance you need when choosing the right roof for your project. There is a UK specific code of best practice for green roofing which is available to download for free from www.greenroofcode.co.uk or from the members of the Green Roof Organisation (GRO), further details of which can be found at www.nfrc.co.uk

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