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Tour of Green Roofs (Shanghai, Day 5)

This is the 5th post in the Shanghai Journal by guest blogger Renee Toll-DuBois of Earth Our Only Home who recently traveled to Shanghai to attend the World Green Roof Conference and the 2010 World Expo.  All text and photographs courtesy of Renee Toll-DuBois.  Previous posts can be read here (day 4), here (day 3), here (day 2), and here (day 1).

This is the last day of the conference. I leave tomorrow and we are visiting a number of green roof projects in the city, both intensive and extensive, using trays combined with pots as well as direct planting. We load into our four busloads (approximately 168 people!) to head out to see the sights. When we drove to the University the other day, I spotted several green roofs from the highway and wonder whether we will be visiting those. It had seemed all in one district so I also wonder if we will be visiting various districts in the city.

First is a cluster of a few dozen sedum roofs in the Yangpu District. There is strong political support for these roofs, which are largely retrofitted onto existing concrete decks. The green roof is created most simply by placing onto the waterproofing layer of the roof pre-grown plastic trays filled with a planting medium that seems to be peat mixed with compost or other materials that has been planted with sedum (which comes in many varieties and was in flower as you can see). The Chinese appreciate the aesthetics of a green roof and value its insulating and hence cooling effect (the summers get very hot here). The challenges local designers are facing however is retrofitting these green roofs onto existing building stock not designed to take extra load so they default to the extensive, thin planting medium layer sedum-style green roof.

Traveling in the company of these experienced international green roof experts, they were looking with an eye for details. I learned that these trays are designed with drainage channels that can be opened or closed and pieced together to direct the drained water where you want, if you lay the trays out with this in mind. I saw the utility of the trays for being easy to install, replace, and redesign if work needs to be done on the roof itself or other issues come up. Trays do seem to be the most popular style and research is being done on how light and thin the planting medium can be and still provide a viable green roof.

Additionally, green roofs are valued for their ability to capture dust and other air-borne particulates and clean the air of pollutants, improving the air quality that is daily declining. Poor air quality, smog, was in evidence to us as we looked out our hotel window and rarely saw a blue sky on the clear good weather days. In promotional materials included with the conference program, other benefits were mentioned including decreasing the "urban drainage load" which I assume to mean stormwater management, absorbing noise, extending the life of the roof/building, saving energy and keeping the building warm in winter and cool in summer, minimizing the heat island effect and saving the cost of investment in land. As I have mentioned however, the air quality and aesthetics seemed most emphasized on our tour and in the program.

Our international delegates seemed to be more in favor of the direct plant method whether for extensive or intensive green roofs. Extensive are the thin planting medium, intensive the deeper planting medium and usually requires irrigation. Irrigation for the thinner extensive depends it seems to me on the climate. In the northeast and upper Midwest, sedum is used as it can go 90 days I am told without water and still survive and in most cases water comes naturally within 90 days. However, when you move into warmer climates more of the year, irrigation becomes a different matter.

From the two different roof tops we could see the same green roofs I saw from the bus the other day and yes they are all in one district. They are all the tray style it seemed except for one or two that appeared to be intensive and provide more variety in plant species and visual height.

Our next stop was the roof garden on the Friendship Shopping Centre which was an intensive style garden, larger than the others we had seen or perhaps merely giving that illusion through its more lush plantings. I saw fruit trees, Japanese maples, palm trees, grasses, bamboo, and ground cover, including the ever popular sedum but other plants as well, demonstrating much more biodiversity than the tray gardens had. These rooftop gardens do provide a pleasant spot to take a break as an employee by simply riding the elevator up to the top floor.

Our next stop was the Dazhing Merrylin Hotel which has a beautiful garden that seemed every bit like one on the ground - expansive, with trees, shrubs, flowers, turf, and many plants that were familiar - rhododendrons, irises are two examples. It sat on the second floor above the reception area of this old-fashioned stone building, providing plenty of weight bearing structure needed for this well-appreciated amenity.

Next stop on the tour was into a different neighborhood to see one of the living walls constructed by the Hainer Eco-Building Company of Shanghai. This wall was planted with the ubiquitous sedum placed into fabric pockets placed in parallel rows down the height of the wall, with irrigation and fertilizer systems feeding into the bags from the back directly. This system provides an option in many locations I am sure where more conventional green roofs or walls would not be feasible but it did seem to be more costly than other techniques we had seen.
A question that continued to come up from among our group was the longevity of the different systems. We were told that since October, less than six months ago, several of the plants in the fabric pouches had already had to be replaced. While this may be an easy process, it seemed that it revealed a system that would require frequent maintenance and the associated costs. We were also told that one of the tray style green roofs had been in existence for 10 years but it was not clear whether it was the same plants and trays there for 10 continuous years or the same overall design but replaced trays and plants. This was part of the mix for our green roof folks as they calculate costs over time and maintenance. In China green roofs may be at a newer stage than elsewhere: innovation is most important now in order to get as much exposure and later a different innovation that focuses on refining and improving different designs will come.

This last day of the conference was a food day as we were treated to a meal in a restaurant at midday and there was a banquet at night with our kind hosts to listen to selections from the Beijing Opera, hear live traditional music, and eat our fill. Toasts were free-flowing as was the beer and soda, the food kept being brought out and fit on the enormous lazy-susan in the middle of the table. It was a fun closing to a packed week. I am told it is important for a host to provide more food that guests can possibly eat and this was definitely accomplished. It also led to interesting conversations about what happens to the extra. I learned there is a charity in Hong kong that comes and picks up this extra and redistributes it to the hungry. We were also told that at the restaurants it often goes to feed the employees.

Tomorrow I leave and will fit in some more sightseeing before I head back to the airport.


Thanks Renee for blogging about the events. For those of us who couldn't attend, it offers a detailed account of what's going on!
Unknown said…
Everyone is concerned about irrigation for green roofs and I would like to point out that it is very possible and a great insurance for the dreaded possibility of drought. My firm has done over 30 roofs with great success, including the Clinton Library and the Target Center. Please visit KISSSUSA.COM

Brooks Paul
Janna said…
nice post!