Managing Stormwater with a Protected Membrane Roof
A Blue Roof PMR assembly mimics natural hydrology systems and is an engineered and biological system designed to manage stormwater.
Stormwater and its effects on our infrastructure, environment and budgets continue to be an ongoing issue in the United States. As more natural open land is paved over for roads, buildings and parking lots, there is less area in which rainwater can infiltrate into the ground or traverse safely and effectively to waterways. This increasing level of impervious cover concentrates more rainwater into smaller areas on its way to being stored in pipes, ponds and reservoirs.
A number of studies have been commissioned during the past several decades to address stormwater management techniques. Vegetated roofs are a tested and EPA-endorsed and approved Best Management Practice (BMP) for inclusion in a project’s stormwater management plan. Vegetated roofs are now becoming a standard BMP in many low impact design/development (LID) projects.
Properly designed vegetated PMR Assemblies have the ability to capture all or portions of a typical rainfall event. This rainwater is stored in several areas of the assembly – within the open pore spaces in the growing media and within the drainage/water retention system that underlays the media.
This total assembly handles this stormwater in several ways:
- It retains a portion of the stormwater until the assembly is completely saturated.
- It delays the release of excess stormwater from the building roof and into the site stormwater system.
- It reduces the volume of stormwater runoff and releases some of this rainwater into the atmosphere by evaporation and transpiration through the plantings.
- It cleans the rainfall of particulate matter and chemicals within acid rain through the filtering actions of the plant material, growing media, system filter and drainage layers.
In these ways, vegetated PMR Assemblies mimic natural hydrology systems like wetlands and similar structures. The complete assembly is simultaneously an engineered and biological system designed to manage stormwater.