Green Roof Resource

While my interest is in the model development side of green roof research, there were several interesting talks on plant performance beyond the characteristics of depth and slope . Kristin Getter from that other large university in Michigan presented results from sun and shade studies of sedum. She noted that while species dominance changed depending on whether the plants were shaded or received full sun exposure, the absolute cover did not change. However, there were differences in biomass production with a shaded roof clearly producing higher amounts of biomass. For climates similar to Michigan, she recommends s. acre, a. cernuum, s. kamschaticum, s. spurium in shade, and a. cernuum, T. calycinum in sun. While this information is useful to many, I am eagerly anticipating Getter’s results on a green roof’s CO2 sequestration abilities. Too bad we have to wait until next year.

Manfred Kohler spoke on studies evaluating installation using vegetated turf mats versus cuttings. His study also showed effects from sun or shade exposure although this was not the focus. Cuttings of sedum outperformed cuttings of grasses due to the slower growth rate of grasses. Grasses became established with the second year. While mats outperform cuttings in the first year, cuttings provide a greater diversity of plant species. It was observed that the grasses did better on the north facing roof while sedum did better on the south facing roof.

In a separate session, strategies were discussed for creating and maintaining successful green roofs in practice. Unfortunately, the talk was not included in the conference program, and I did not catch the speaker’s name although she’s worked on a number of green roof projects in the DC-Baltimore area. She showed a variety of roof “failures” and her investigations to determine the source of the failure. Wind affected several of her projects through scouring and increasing rates of evaporation. Excessive sun and shade also proved disastrous when plant selection and irrigation schedules were not compatible with the soil media depth and roof’s orientation. While this certainly is a fair challenge for the landscape architect or horticulturist, I also feel that there is a role for the engineer. Of course speaking from the hammer’s perspective, things can only improve upon hammering. Regardless of my bias, engineers can determine from location and building orientation the effects on the rate of evapotranspiration from wind and sun/shade exposure, which would assist in plant selection.

This year’s Greening Rooftops for Sustainable Communities conference was held April 29th through May 2nd in Baltimore. Treehugger summarized the award winning projects here. Green Roofs for Healthy Cities has provided detailed descriptions of the winners.

The sessions were held on Thursday and Friday, and I focused my attention on the policy and research tracks. On Thursday morning, Dr. Hamid Karimi from DC’s Department of Environment presented the District’s efforts to encourage green roofs and other green infrastructure. While San Francisco has received a lot of press concerning a new ordinance that would require most new commercial and residential buildings to be LEED certified, DC’s Green Building Act of 2006 is the first major US city to require LEED for private projects. By 2009 publicly financed buildings within the District must achieve LEED Silver Certification, and by 2012 privately owned buildings must also achieve LEED Silver Certification.

In addition to establishing green building standards, the District is also tackling water quality and erosion issues. For soil erosion and sediment control, sites must retain a 0.5 inch in 24 hours storm event onsite, and those sites along the Anacostia River must retain 1.0 inch in 24 hours storm event. The Department of Environment is currently revising stormwater fees to provide financial incentives for low impact development (LID) technologies. The current fee is associated with water usage while the new system should focus on impervious surface area. This fee structure will aid incentives such as the green roof grant within the municipal separate storm sewer system (MS4) permits. Expedited permit reviews for green projects are also under consideration.

A different approach to encourage green roofs is under development in New York State. Amy Norquist of Greensulate LLC spoke of a green roof tax abatement for $6.75 per square foot of green roof. The New York State Senate bill S07745 refers to a credit of 55% of expenditures up to $5000. The New York State Assembly bill A10234 provides greater detail. These have yet to be approved but are a clear example of states beginning to direct cities toward innovative LID technologies.

The federal government is not silent on this issue either. Dov Weitman spoke about EPA’s efforts to promote green infrastructure within the framework of the National Pollutant Discharge Elimination System (NPDES) program. EPA’s green infrastructure site provides a wealth of information describing various technologies (including green roofs), research activities, policies, and case studies.

A variety of energy related topics were presented at the topics. One of the most exciting announcements relating to green roof environmental benefit valuation was the new module for EnergyPlus, a building energy use and cost analysis program that uses DOE2 for the analysis. The new ecoroof module gives the user the ability to model the energy savings due to a green roof. The module was a collaborative effort by Quantec and David Sailor at Portland State University. Quantec is currently developing a web-based tool for assessing the energy benefits of green roofs based on the module within EnergyPlus.

An architectural engineering student from Penn State, Paulo Cesar Tabares Velasco presented preliminary findings of heat flux through a vegetated roof based upon data taken from a climate chamber, which is part of the Building Environment Simulation and Testing Facility. Tabares Velasco is evaluating the flux to determine an associated R-value for the green roof under various conditions. The experimental setup looks really neat and can control for temperature, humidity, and air flow rate.

One of the benefits of green roofs that has been touted for several years is the improved efficiency of solar panels when used in tandem with green roof systems. Manfred Köhler collaborating with Stefan Krauter is exploring the synergy further at the ufaFabrik Berlin where several PV systems are installed above vegetated roof systems. They have seen improvements in efficiency as well as improvement in plant number an growth.

It’s time for the annual conference review. I spent most of my time in the research track, so this year’s review is a little limited in scope. First, I was quite impressed with Minneapolis. They have a light rail system from the Mall of America and the airport to downtown. It even goes by a recycling center with a green roof on top. I was impressed with the diversity of restaurants (including one with a green roof for lawn bowling).

Several of the talks focused on stormwater with a greater focus on water quality than in previous years. Lisa Rocha from the Toronto and Region Conservation Authority and Robert Berghage from Penn State both mentioned elevated phosphorus and phosphate concentrations in green roof runoff. Rocha emphasized that while concentrations of nitrates were elevated, the total mass of nitrates were less. A full report of the observations by the TRCA can be obtained here. Berghage included observations on the buffering capacity of green roofs in addition to the observations on nutrients and metals. He also stressed that loads and concentrations from green roof systems should be compared not only to conventional roof systems but also to other landscaped areas. There is concern that by not comparing green roofs to landscaped areas, one could make the otherwise irrational argument of paving up to a waterway as a best management practice for the prevention of nutrient runoff.

Barbara Deutsch from Casey Trees enthusiastically presented on collaborative work with Limno-Tech, Inc. evaluating stormwater management impacts from large-scale green roof scenarios for Washington, DC. It was found that greening efforts could result in operational savings between $1.4 million and $5.1 million ($0.01/gallon) annually due to decreases in water pumping. The full report should be available online by the end of this week from Casey Trees.

Stay tuned for further updates from the conference.

On Friday, I listened to Nigel Dunnett and Rosemary Coyne speak about projects in Sheffield and Birmingham both in the UK. Both cities have an industrial past, which gives hope for urban renewal and greening for Southeast Michigan and Detroit. In between Nigel and Rosemary’s presentations, Sandra Marshall spoke about policies encouraging green roofs from around the world. The policies focus on direct and indirect incentives but have expanded in recent years to move beyond stormwater management to include energy savings and the urban heat island effect. More information on this can be obtained from the Canadian Mortgage and Housing Corporation who funded the research for a report.

I split the afternoon session between policy and research. The policy talk by Hitesh Doshi, at Ryerson University in Toronto, quantified the benefits of green roofs at the city scale. The second talk was by Marco Schmidt, a professor at the Berlin Institute of Technology, who is investigating the use of vertical green walls on building exteriors.

Sunday morning I went to the Harvard Museum of Natural History where there is currently an exhibit on climate change and global warming. They had a nice active learning portion where you can vote your opinion on reducing US carbon emissions or funding low carbon technologies in developing countries. Additionally, they included information on how scientists take ice cores and deep ocean sediment cores to understand how the climate was thousands of years ago. However, the rest of the exhibit lacked strong and coherent evidence that the climate is changing. For the layperson or a child, much of the information would be difficult to understand. This is part of the reason why there is such a knowledge gap regarding climate change. It is difficult to present a convincing argument that is easy to understand. I look forward to seeing how well the argument is presented in the new documentary, An Inconvenient Truth.