Sourced from Buildings
Green roofs are a challenging proposition for existing buildings because not every structure can handle the extra weight or maintenance. But buildings that can bear the load tend to perform better, and they also showcase the owner’s commitment to sustainable building operation. Building owners have many reasons to invest in green roofs, but these five green roof benefits are cited most often.
1. Local Requirements
Some areas, such as Washington, require at least part of the roof to be vegetated, explains Matt Biesecker, senior designer for LandDesign. The requirements are typically based on environmental impacts, such as energy efficiency.
In the capital’s case, the requirements are intended to mitigate stormwater discharge. Green space is measured by a metric called the Green Area Ratio (GAR), which assigns points to various landscape elements that are weighted according to their environmental value. Intensive vegetated roofs with more than 8 inches of growing media are weighted more heavily than extensive roofs with 2-8 inches, for example.
All new buildings must achieve at least the minimum GAR value allowed in their zoning district. Existing buildings with additions or interior renovations must comply if the construction cost of the project is more than the assessed value of the improvements.