The Future’s Green

The Green Roof Centre.

I

n the last few years green roofs have shifted from a horticultural curiosity to an accepted mainstream technology. Self builders and architects have taken this green technology on board due to

the benefits it not only brings to the build itself, but also the environmental, social and economic benefits as being one of the more visible forms of sustainable technology. Green roofs are not a new concept. The insulating properties of soil and vegetation have been utilised for thousands of years, cooling buildings in Africa and helping to retain heat in the traditional earth sheltered huts of the Viking era. Currently technological advancement is being led by Europe with Germany boasting a £39 million industry. European policies are in place to encourage the growth of the industry and financial incentives are offered for installations.

Types of Green Roof

A distinction is usually made between

‘intensive’ and ‘extensive’ green roofs associated with the amount of care they require. Intensive green roofs are composed of relatively deep substrates (70 – 150+mm) and can support a wide variety of plant life. These systems are heavy when saturated and often require additional support from the building’s structure. More contemporary intensive green roofs can be visually and environmentally exciting, integrating water management systems that process waste water from the building as well as storing surplus rainwater in constructed wetlands. However, due to larger plant material and horticultural diversity, intensive green roofs can require substantial input of maintenance resources, the usual pruning, clipping, watering and weeding, as well as

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irrigation and fertilisation. A more cost effective solution is an extensive

system which requires little, if any, maintenance. These systems are lightweight due to shallower substrate depth (30 – 100mm) but support a more limited group of vegetation. There are several types of extensive system available, the most common being the sedum mat which is composed of a low growing and drought tolerant vegetation known as sedum. Another extensive system is the wildflower meadow which has high biodiversity value and provides a colourful alternative to the sedum mat. They are usually created with seed mixed of native wildflowers and grasses typical of dry habitats. A cross between intensive and extensive

green roofs is known as semi-extensive. These types of green roof are of slightly greater depth than extensive systems (100 – 250mm) allowing for a greater diversity of plants to flourish. Based in the same principles as extensive roofs they are light weight and generally low maintenance. ‘Brown roof’ or ‘biodiversity’ roofs on the other hand aim to recreate brownfield habitats which are continuously being lost to development. Substrate on these roofs is composed of the by-products of the construction process, such as crushed brick and subsoil, which is left to colonise naturally or is seeded with brownfield

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species such as the snapdragon or poppy.

Energy Saving

The insulation offered by green roofs considerably lowers cooling bills. German studies estimate that even light weight green roofs can offer electricity savings of around £5.20m2 per annum whilst The National Research Council for Canada recorded that a green roof on a 122m2

test facility reduced the average daily

energy demand to air condition the building by over 75%. Green Roofs help cool buildings in two main

ways. The roof surface does not heat up to the same extent and that heat is not transferred into the building. Secondly water evaporating from the plants on the green roof cools the roof itself. Green roofs also help reduce the ‘Urban Heat Island Effect’. Urban areas can be up to 7o

C

warmer than the surrounding countryside due to the large areas of asphalt and other dark materials they contain.

Planting a green roof brings to the forefront a sustainable technology, which gives benefits not only in an energy saving solution to the self builder but to the environment as a whole.

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