Green roofs big & smallAlison Marsden
There has been quite a surge of interest in Green Roofs over the last few years, although the first ones were created in 1960s. There are several key differences between a green roof and a roof top garden although obviously both involve plants growing on top of a building and require a flat, structurally strong and waterproofed roof. All planting helps to take up carbon dioxide and especially in urban areas can moderate temperatures and reduce air pollution. But the primary aim of a green roof is environmental whereas roof gardens are to be enjoyed by people in the same way as a street level garden. Green roofs are designed for the minimum of maintenance once installed: initial watering until the plants are established and thereafter inspection to ensure that there are no blocked drainage holes or pipes and to remove the inevitable unwanted naturally seeded plants before they take over the planned planting. Having plants that do not need constant watering, in addition to natural rainfall is vital – indeed one of the benefits of a green roof in a built up area is to capture and re-use rainfall, reducing the risk of localised flooding. How much maintenance is practical for any roof depends on where it is and what realistic access is available. And this in turn influences the plants that are used: minimal access roofs on a 10 storey building are limited to low maintenance, mat forming plants such as creeping Sedum varieties. If you can regularly and safely get onto the roof – or reach it from the ground – then this opens up perennial plants that need cutting occasionally including wildflower meadows that will support more wildlife.
The benefits and viability of green roofs have been proven by large office block installations but they are equally practical on a small scale. If you are reroofing a shed then why not consider a green roof? You will need a frame to contain the lightweight planting material on a waterproof lining and this can be set at a slope of up to 20 degrees. I have even seen a green roof on a wheelie bin store adding biodiversity to an urban front garden and a whole new meaning to ‘green bin’. Plus it is a lot more attractive. That’s a real bin-win-win!
Happy Gardening from Alison
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