Ask The Expert
01/01/2012
Do green roofs place more of a burden in terms of weight on the rest of the structure?
The weight of a green roof build up varies according to the depth of substrate used.
There are two very important considerations. One is the maximum weight of the green roof, when fully saturated and it is vital to check that the roof structure can support this load.
The second is the minimum weight per m2 which is vital for wind uplift calculations purposes, especially when a roof is almost entirely desiccated during a n extended dry spell. It is essential to ensure that the roof build up can resist the maximum uplift loads to which it is likely to be subjected.
The necessary minimum dry weight depends on many factors for example the location, the height and the geometry of the roof. A low level roof in the middle of a city centre doesn’t need as much resistance to wind uplift compared to a high rise coastal installation.
By opting for a lightweight modular solution, installation is simpler and there is no need for penetrations. Typically, a modular green roof comprises just two elements: a fleece layer which is rolled out, and the pre-grown and pre-established planting, grown within the cuspated layer and simply placed upon it.
Pre-grown and established plants such as sedum or sedum mix with wild flowers and grasses are much less susceptible to initial wind uplift and need no watering in situ.
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