One of the rarely mentioned benefits of installing a green roof is the extended life of the waterproofing membrane. In today’s culture, too few looks at matters for the long term. However, I have noticed over the last 10-15 years that long term building owners are most of the clients paying the initial premium associated with green roof installations, versus the installation of conventional gravel/ballasted or black roofs. Clients such as, colleges/universities, hospitals and government building owners are implementing green roofs because of the long-term return on their investment, (ROI). Typically, the (ROI) is 8-20 years. They have this understanding, by way of running a cost-benefit analysis.
It has been stated by many that the green roof membrane's life expectancy is extended anywhere from 2-4 times the typical 15-25 year warranty provided by regular membrane manufacturers. So, the life of your green roof membrane could be between 30-50 years. Of course, there are many factors which will determine that. Green roofs in Berlin, Germany have shown they can protect roofs after 100 years, (Handbuch der Architektur, Berlin, 1889). The green roofs of Rockefeller Center in New York City, for example, have had the same waterproofing membranes that were installed in the 1930’s.
The factors which are detrimental to a black or gravel roof are ultra-violet light, fluctuation in temperatures, wind, ice, snow and rain. By having layers of fabric, soil and plants on top of the waterproofing, “blankets” the membrane, therefore protecting it from those elements. It is buffered from temperature extremes and daily expansion and contraction of the roof materials.
This is the last blog post on green roofs for now, we hope to continue learning and growing with these beneficial practices!
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