From a purely economic perspective, the positive impact of a vegetative ‘green’ roofing assembly is measured in the long term—40 years or more. This means ensuring its performance and safety over an extended period is crucial. A green roof protects the underlying waterproofing membrane from the elements. Combined with a higher-quality membrane necessary to resist soil and plant forces, the result should be a longer roof lifecycle decades beyond a conventional system’s 20 to 25 years.