I had the pleasure of listening to Tad Radzinski, of Sustainable Solutions, a sustainability expert in the Philadelphia area, talk about an unusual and creative project that he recently worked on using a vegetative roof.
From the Building Science perspective, what I like about vegetative roofs is the albedo of plants, which plays a large part in the benefit of live roofs, and the fact that they are literally cool roofs that naturally increase the insulation value on your structure (the r-value of the soil bed). Live roofs also reduce the amount of storm water runoff and city’s like Philadelphia are starting to reward building owners for moving to vegetative roofs.
A few facts:
1.) For most of us on municipal water, when you pay for a gallon of water you are also paying for a gallon of sewage treatment.
2.) In older municipalities, the storm water and sewage lines are co-mingled.
3.) When there is a rain event it can cause the water/sewer to overflow system capacity and be diverted into the rivers.
4.) When this occurs, the municipality is fined for the overflow. However, most cities would rather pay the small fine from the occasional rain event than to upgrade the storm water and sewage system.
Philadelphia recognized this and has started to reward builders who take steps to reduce site run-off by reducing the per gallon rate paid for the water they do use. By demonstrating the volume of run-off eliminated through the implementation of vegetative roofs and the reduction of hard surfaces such as paved parking areas, builders can qualify for water rate reductions. Applying this data to a life cycle assessment, we quickly see one more way that being green can save you green.
Lucas Hamilton is Manager, Building Science Applications at CertainTeed Corporation