Extending Roof Life
If green roofs are constructed correctly they will last longer than conventional roofs with obvious cost benefits. When annual costs are computed over the life expectance of the roof, green roofs can save money and can increase property values.
Green roofs have a longer life expectancy than conventional roofs and most cool roof technologies. Green roofs typically last twice as long as conventional roofs.
Green roofs need to be built to a higher standard than conventional roofs, partly because of their greater weight and of course, it is essential that they are totally watertight. The resulting roof will last longer as a result of the protection given by the substrate and vegetation.
An exposed roof membrane absorbs solar radiation during the day and the surface temperature rises. It re-radiates the absorbed heat at night and the surface temperature drops. These daily temperature fluctuations create thermos stresses in the membrane and in addition ultraviolet light will contribute to degradation.
A major problem with conventional flat roofs is that water tends to pool rather than run off, so allowing water time to exploit any weakness in the membrane. Green roofs will greatly reduce this as the substrate and vegetation will hold much of the water falling on to the roof.
This is because the plants and substrate reduce the exposure of roofing materials to extremes in temperature and UV light, which results in their degradation over a period of time.
Results from many studies show that exposed roofs experience much higher temperatures than that of green roofs. On a study in Toronto, Canada, the membrane on an ungreened roof reached 70 degrees C in the afternoon, whilst the adjacent green roof remained at 25 degrees C.