General Summary

The trip was indeed worthwhile. Robert Herman made a tremendous difference in what could be learned because many of the company tour guides and researchers spoke little or no English. I was impressed with the amount and quality of extensive green roof research being conducted at several Institutes and Universities in Germany. Dr. White and I had many opportunities to compare notes on what we observed and talk about future research at Penn State University and the involvement of companies such as Garland Roofing.

Most large cities in Germany require new buildings replace their impermeable footprint area with equivalent green space. The only way they can comply with this law is with green roofs. Tax breaks and other financial incentives have been discontinued. Extensive green roofs are grown mainly in coarse aggregate mineral substrates with only 10 to 20% compost or peat and no perlite or coir (coconut) fiber. Crushed roof tile chips are used most often as the drainage layer with a filter fabric over the top. Using many of their aggregate materials would be unlikely in the US. For example, the weight of crushed tile ( of crushed brick in the US) would be too heavy on our lighter weight construction. Also, the cost of shipping these materials from a central distribution point in the US would be prohibitively high. Therefore, we believe that regional, or even local, sources of drainage and aeration materials would need to be developed.

They use irrigation only for the first year. Sedums and grasses are the predominate species used.
Prices of green roofs in Germany have declined from $4.50 to less than $2.00 per square foot in the past 10 years because of very strong competition among installers.

Landscape Architects are mainly used for intensive green roofs. Lightening rods, safety anchors, ropes and harnesses are required by law. Gravel firebreaks, every 40 square meters and gravel perimeters are required by law.

I conclude that the climate of Germany (USDA hardiness zones 6 and 7), the competition for green roof jobs and the availability of drainage materials, substrate products and plants, especially sedums, precludes their technology and pricing from being relevant in North America anytime in the near future. We must develop our own technology and stimulate an interest among horticulture and landscape firms in this new market opportunity. Basic and applied research is needed.