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.

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6 comments on “Four Green Roof Questions With PSU’s Robert Berghage

  1. Anonymous

    Let’s hope that there is a lot of research going into edible crops for the plant material. Sedum itself just hasn’t made it into the food pyramid.

  2. Anonymous

    We are a wholesale nursery that grow many types of Sedums as well as other plants that are suitable for green roofs. We’ve been trying to break into the green roof market for several years with no luck. Do you have any suggestions for these companies that need growers of green roof plants? Why does there seem to be a lockout to those of us that grow quality plants? We would be happy to provide material needed for the installers that are not using the trays that are on the market.

  3. Anonymous

    I’m very surprised that a green roof expert would choose a tray system over a built-in-place system (in most cases)
    I don’t believe his statement has scientific backing. If there is one, I would like to hear about it.

    Just look at the history of green roofs in the European market. The tray system has pretty much disappeared in the industry.
    I see a place for tray systems in the market. However, introducing plastic trays on a green roof simply doesn’t make much sense to me.

    The cost of plastic is an added cost to the customer while they trays don’t serve a purpose after placement on the roof.
    This is most likely the reason that you don’t see a lot of trays used anymore on large scale projects. It’s simply not price competitive.

    Also, trays do not benefit the health of the vegetation inside the module. Most tray systems are starting to fail due to overheating of vegetation in the summer (black edges of the tray warm up and burn bordering vegetation).

    The State of Wisconsin has so many negative experience with tray systems that they have banned this system from all public projects. (I guess i’m not alone in my standpoint)

    I don’t mean to completely burn the use of a tray system (ok, maybe just a little bit). My point is that we have the luxury of several decades of green roofing experience in the European market. Why not learn from it instead of re-inventing the wheel.

  4. Anonymous

    Let’s hope that there is a lot of research going into edible crops for the plant material. Sedum itself just hasn’t made it into the food pyramid.

  5. Anonymous

    We are a wholesale nursery that grow many types of Sedums as well as other plants that are suitable for green roofs. We’ve been trying to break into the green roof market for several years with no luck. Do you have any suggestions for these companies that need growers of green roof plants? Why does there seem to be a lockout to those of us that grow quality plants? We would be happy to provide material needed for the installers that are not using the trays that are on the market.

  6. Anonymous

    I’m very surprised that a green roof expert would choose a tray system over a built-in-place system (in most cases)
    I don’t believe his statement has scientific backing. If there is one, I would like to hear about it.

    Just look at the history of green roofs in the European market. The tray system has pretty much disappeared in the industry.
    I see a place for tray systems in the market. However, introducing plastic trays on a green roof simply doesn’t make much sense to me.

    The cost of plastic is an added cost to the customer while they trays don’t serve a purpose after placement on the roof.
    This is most likely the reason that you don’t see a lot of trays used anymore on large scale projects. It’s simply not price competitive.

    Also, trays do not benefit the health of the vegetation inside the module. Most tray systems are starting to fail due to overheating of vegetation in the summer (black edges of the tray warm up and burn bordering vegetation).

    The State of Wisconsin has so many negative experience with tray systems that they have banned this system from all public projects. (I guess i’m not alone in my standpoint)

    I don’t mean to completely burn the use of a tray system (ok, maybe just a little bit). My point is that we have the luxury of several decades of green roofing experience in the European market. Why not learn from it instead of re-inventing the wheel.