Four Green Roof Questions With PSU’s Robert Berghage
GG: What is your impression of the green roof market here in the United States in its current form and is there potential for growth?
RB: The market is interesting. There are actually a fair number of players. LiveRoof and some of these other roofing companies are providing plant material to provide plants in local markets. There is definitely a market there.
From a market analysis standpoint, the potential is just astronomical. Whether we ever reach that potential is an interesting question. When you think about the number of flat roofs in North America and the total potential space you could be greening, it’s just enormous. At this point, it’s more of a boutique market as only a small percentage of roofs are being greened. The market is very much in its infancy, but that may change as the pressures continue to mount on municipalities and urban areas.
GG: What are the main drivers of the green roof movement?
RB:The driver in most urban areas is combined sewer systems and combined sewer overflows. If you think about a commercial building in a city, between the parking lot and the structure itself you don’t have a lot of places to put water.
GG: Which of the two green roof systems makes the most sense: the modular or built-in-place system?
RB:The modular systems make the most sense to me. You need to be able to green it off site, like at a greenhouse or a nursery, and put a finished product into place. In areas where a smaller roof or logistics are difficult, those factors are driving the cost of systems. If you talk about the post office in New York City, it’s one of the biggest green roofs in North America. When you talk about these huge structures, then it makes sense to do a garden.
GG: What are the opportunities in green roofs for growers?
RB:It’s in supplying the plants. The thing that really freaks out people when they start talking about these projects is the numbers–for sedums especially. Fifteen years ago, someone who grew sedums as a crop might grow a few hundreds of this species, and maybe 1,000 of something else. And that was a pretty big number for sedums. For a roofing system, if you’re doing plugs, consider that it’s 2 ½ plants per square foot. We have one roof on our campus and that’s 50,000 square feet. So that roof alone has 125,000 plants.
The market is still small. The big jobs call for large numbers of plants. Sometimes, the roofing companies have issues trying to find the numbers of plants they need. There are a couple of nurseries that have done really well at making this a large portion of their product line. This is what they do.