GREEN ROOFS

Green roofs are not a new idea. In fact, like many of the best 'new ideas' they have been standard construction practice in some countries for hundreds (maybe thousands!) of years. In the cold climates of Iceland and Scandinavia sod roofs helped to retain a building's heat, while in warm countries such as Tanzania, they keep buildings cool.

Until the mid-20th century green roofs were viewed mainly as a vernacular building practice. However in the 1960 's, rising concerns about environment and the lack of green space in urban areas renewed interest in green roofs as a "green solution". The renaissance began in Germany and Switzerland where new technical research began into plant suitability, membranes etc.

Unlike a roof garden or ‘intensive’ green roofs, ‘extensive’ roofs are not designed for human use. The key benefits of including and ‘extensive’ green roof in your garden design include:

High water retention

water is released from the roof more slowly helping to prevent damage by flash flooding and high rainfall

Improved biodiversity

provides a habitat for animals and plants. Especially important in urban areas with little green space.

Improved environment

• Absorbs greenhouse gases.

• Absorbs air pollution and dust.

• Cools and humidifies the surrounding air.

Recycled materials

• Many of the materials used in green roof construction are manufactured from recycled building materials, plastics and rubber which helps to reduce landfill disposal.

Insulation

• Extra insulation helps to retain heat and therefore reduces heating bills

• Insulating effect also reduces noise levels - which is especially important in urban areas

TYPES OF EXTENSIVE GREEN ROOFS

1. Sedum mats

Sedum mats are pre-grown and delivered to site like a rolled up carpet. It is laid on a 5 - 7cm of growing medium (standard method) or direct onto a moisture retention blanket (ultra light weight method). Sedums are used because they are wind, frost and drought resistant.

2. Substrate based roof

7cm of crushed recycled brick is placed on the green roof system and plug planted with sedums or with sedum mats applied. Some green roofs are made of turf but this is not generally the case in the UK

3. Green / Brown roofs for biodiversity

These are quite like substrate based roofs but can use recycled aggregate from site and are generally left to colonise naturally or seeded with an annual wildflower mix.

In the UK, sedums are probably the preferred and most low maintenance solution. They need little watering and only a thin, lightweight layer of substrate on which to survive. They look ttractive all year round, changing colour through green, pink and purple - without going through the scruffy phase that grasses and herbaceous plants can suffer from – and without needing cutting back.

GREEN ROOF EXAMPLES UK

BedZED

20-30 South Collonade, Canary Wharf

Rolls Royce, Goodwood

USEFUL SITES

Livingroofs.org

thegreenroofcentre.co.uk

Alice Bowe is an award winning garden designer, writer and columnist for the Saturday Times. For more information on her sustainable garden designs visit her website www.alicebowe.co.uk