As our summers become increasingly hot for longer periods people will be looking to a range of strategies in order to stay cool in their homes and workplaces. One such strategy, already being widely used in other parts of the world including Germany, Austria and Singapore, is green or “living” roofs, roofs on which grasses, flowers or small shrubs are growing.
Such roofs have a long history. In Viking days turf-covered roofs in Scandinavia provided effective insulation from the cold. But these roofs are also effective in insulating buildings from heat.
Modern living roofscapes depend on a series of carefully designed layers which protect the roof and ensure that rainwater is filtered and drained and that the plants growing there can thrive.
The conventional roof serves a sole purpose – protecting the building and its inhabitants from the elements. In doing that it takes a beating from sun, wind, rain – and, in colder climates, snow. On a hot day temperatures on conventional roofs, particularly dark-coloured roofs, are much higher than the surrounding air. This makes it more difficult to cool the air in the building below. In addition the hot roof contributes to the urban heat island effect.
Up-front costs for green roofs are higher than for conventional roofs and some maintenance is required.
However, there are substantial benefits from these roofs. As the soil and vegetation act as living insulation, the building’s internal temperatures are moderated – so it is cooler in summer and warmer in winter. Less energy is needed for cooling or heating which means both greenhouse gas emissions and energy costs are lower. Other benefits include reduction of rainwater runoff, filtering of air pollution by the plants, support for biodiversity within an urban landscape and reducing the urban heat island effect.
A different roof strategy involves the development of cool roofs – roofs which use of reflection to send solar energy back into space. A variety of forms has been developed including light-coloured metal, shingles, tiles, coatings and membranes. In an increasingly warming world sending solar energy back into space rather than absorbing it is essential.
- Leonie Blain
This article was originally published in the VOICES FOR THE EARTH column in The Daily Examiner on January 21, 2019.