Does a green roof buffer water?

Yes, every green roof absorbs and buffers water. However, a Purple Roof retains more water than any other green roof concept. The Purple-Roof is the only concept that has been exposed to real life assembled testing in a professional setting.   

Stormwater Testing Laboratory

We need to think differently about the main purpose of a green roof, which is to retain and detain water during a large stormwater event.  In order to demonstrate that green roofs are legitimate stormwater solutions, the green roof industry needed a formal platform to test and demonstrate the behavior and performance of any green roof system. The Stormwater Laboratory is an initiative of Sempergreen with the support of five of the largest green roof system providers in the US.

Goal of the Stormwater Laboratory

The goal of the Stormwater Laboratory is to be able to test fully assembled green roof systems on a large scale, and expose them to a standardized replicable test. Civil engineers thus far relied on basic ASTM tests of individual components that did not tell the complete story. Testing complete assemblies, and exposing them to replicable rain events tells the complete story, it will reveal the impact of each layer upon the complete system once assembled and tested, which is always less than the sum of the ASTM results.  

Compare different systems in identical setting

The Stormwater Laboratory will allow the industry to compare different systems in an identical setting, and provide solid performance data which civil engineers can use to model Stormwater conditions for any given project, and apply the green roof system that fits the civil engineer’s stormwater retention and detention needs.

Increasing water retention capacity while saving costs

For instance, exhaustive testing in the Stormwater Laboratory showed that systems utilizing Urbanscape Hydro-blankets (needled mineral wool) demonstrate to retain and detain 2x as much water compared to conventional 4” deep systems, and the same performance when comparing to an 8” conventional system, thereby increasing the water retention and detention capacity of a system while saving substantial costs.  


Stormwater Lab for Green roofs


Purple Roof retains more water than any other green roof concept

Climate change means that the intensity of rainfall is increasing all over the planet. Sewage systems are not always capable of dealing with large volumes of rainwater. In recent years, rivers have overflowed more frequently and vast areas have been flooded. This usually causes considerable economic loss and environmental damage. In order to absorb this large amount of rain water, water buffering on roofs is becoming increasingly important, especially in urban areas where green space has had to make way for roads and buildings. Research shows that a green roof can significantly reduce the amount of water that flows into sewers, even by as much as 70-95% in the summer. A Purple Roof retains more water than any other green roof concept. 

Purple Roof Retention Comparison

Read more about Purple Roof and Stormwater Management