Growth in Vegetated Roof Popularity

During the years I lived in Europe, I fell in love with the vegetated or “green” roofs I saw throughout The Netherlands and Germany. The concept seemed simple and logical; use otherwise unused roof space for vegetation that lends to environmental, economic, and aesthetic benefits. After further research, I learned that building vegetated rooftops is more complicated than it looks, but nonetheless there are excellent benefits, and it’s great to see their growing popularity within the United States.

Germany is credited with initiating vegetated roof efforts as they have been developing and installing them for over 40 years. It has been to our benefit in the United States to access German research and building models that have been tested across many years.

The two categories of vegetated roofs are Intensive and Extensive. Extensive vegetated roofs have soil 6 inches deep or less and their design is more focused on performance. Intensive vegetated roofs require a minimum of 1 foot of soil depth and they often include a more traditional garden with large trees, ponds, shrubs, and benches.

The basic extensive model includes a waterproof membrane, a drainage layer, and a growth medium.

According to the Whole Building Design Guide (WBDG) benefits include:
1.) Controlling storm water runoff
2.) Improving water quality
3.) Prolonging service life of roofing materials
4.) Reducing sound reflection and transmission
5.) Creating wildlife habitat
6.) Improving the aesthetic environment

On the flip side are cost and the many design factors that must be taken into careful consideration. Building vegetated roofs requires a concerted effort between the disciplines of horticulture, waterproofing, and engineering.

The WBDG outlines the following design factors:
1.) Climate, especially temperature and rainfall patterns
2.) Strength of the supporting structure
3.) Size, slope, height, and directional orientation of the roof
4.) Type of underlying waterproofing
5.) Drainage elements, such as drains, scuppers, buried conduits, and drain sheets
6.) Accessibility and intended use
7.) Visibility, compatibility with architecture, and owner's aesthetic preferences
8.) Fit with other "green" systems, such as solar panels
9.) Cost of materials and labor
10.) Local fire code restrictions
11.) Orientation of the building as it relates to surrounding buildings and shading
12.) Security and fall protection
13.) Required maintenance

I was thrilled to see an article in San Diego Magazine highlighting Building Green Futures, a company developed in the past 5 years to service the San Diego market for vegetated roofs and water reuse systems. I’ve seen some of the green roofs in New York, Chicago, and Portland, but not in San Diego. It’s great to see this sort of company surfacing locally. I have high hopes of one day owning a house with a vegetated roof and goats to enjoy the greens!

Additional Information can be found at the following sites:

Whole Building Design Guide - This site includes a lot of detailed information on vegetated roofs. The list of resources at the end of the article includes all sorts of books, publications, websites, and research. It also includes design and analysis tools and manuals.

Green Roofs for Healthy Cities - This site is dedicated to communicating the benefits of Green Roofs and how to address the barriers to building them.