For those who are in a position to extend their gardens to their roofs, benefits include a potential increase in the amount of garden space and wildlife habitat, and reduced heating and cooling requirements, as they can act as added insulation in the winter and a cooling feature in the summer. Green roofs slow the weathering of roofs by protecting them from the elements, and filter pollutants out of air and rainfall.

Green roofs come in many different forms. Some can be very heavy and require extra support whilst others need little more than a waterproofing layer. They can be used on buildings of any size, from garden sheds to office blocks.

Living Roofs: An independent green roof information and research resource

A working example in Mendip: The Charterhouse Centre

When the Charterhouse Centre, in the Mendip Hills, needed to extend and revamp it was decided to build the new student accommodation wings in a sustainable way and find ways to improve the environmental quality of the existing buildings.

Motivation: Work needed doing and it made sense to make the work environmentally and socially sound in both design and construction, especially given that the centre was focusing more heavily on environmental education.

Practicalities: A green sedum roof was among the new features installed, all of which were found to be worth the effort and initial capital outlay, both in terms of performance and general 'feel good' factor. The sedum roof mat is lightweight, requires little maintenance and is drought resistant. It has practically no run off, requires very little attention, has grown in species diversity and is an attractive environment to sit near during lunch breaks.

Other sustainable features: The centre promotes environmental awareness to all its school groups and aims for maximum energy and water efficiency in its everyday running. For example, low flush toilet cisterns have been fitted, which have paid for themselves already due to the reduced frequency with which the septic tank needs emptying.

Top Tip: 'Persist with new technologies and systems. They may have problems in the early days, but once you have ironed these out they are effective, efficient and much better for our environment.'