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The G.R.E.E.N. Research Report
April 2008

The great FROZEN green roof project

By Dr. Bill Retzlaff, The G.R.E.E.N. Editor
All Photos Courtesy Bill Retzlaff and Kelly Luckett

Dr. Bill Retzlaff

Dr. Bill Retzlaff

I’m Dr. Bill Retzlaff (above photo, in the “hat”) and I am the Coordinator of the Green Roof Environmental Evaluation Network (G.R.E.E.N.) located at Southern Illinois University Edwardsville (SIUe).  G.R.E.E.N. is a research cooperative between SIUe, Green Roof Blocks™, Jost Greenhouses, Midwest Groundcovers, Midwest Trading and Horticultural Supplies, JDR Enterprises, Emory Knoll Farms, and Greenroofs.com that has been established to evaluate the performance of green roof technology in the Midwestern United States.  Faculty, Student Researchers, and Collaborators are working together to evaluate green roof performance and green roof technology and to make the information available to users for development/establishment of green roofs.  More detailed information about G.R.E.E.N. can be found at our web site (www.green-siue.com).

The primary goal of G.R.E.E.N. is to address issues of concern to the green roof industry in the Midwest and at other green roof locations nationwide using scientific (hypothesis-driven) research evaluations.  Relevant to this article, most of our research projects are right on the SIUE campus while some are at locations further away (like the project in Chicago in this article).  Our ancillary goal is to educate students (potential future industry leaders) about this emerging environmental technology by engaging them in green roof research.  It is rare that classroom education is coupled with practical, hands-on experience with an emerging technology – our students hear and learn about green roof technologies in the classroom, then develop and implement their green roof experiments on the roof and in the field.  In addition, each student’s research discoveries and outcomes help guide future research and industry directions in the development of green roofs. In my first Greenroofs.com research reports, I described our fully replicated green roof storm water trials and reported in depth about our research results.  In this report, I’d like to talk to you about a commercial installation that became a “research” project – with an interesting outcome and valuable insights regarding seasonal placement of green roofs.

Mark and Mike Crowell are on the EPDO membrane (with breath showing) and you can see the frozen highway embankment in the background. It was about 5° F at this time on December 9th, 2006.

PROJECT DESCRIPTION
One of the things that I do as often as possible is to go along with my green roof collaborators on their commercial installs.  This allows me to have hands-on experience with many types/kinds of installations and also to evaluate potential pitfalls and shortcomings for future research projects.  Besides, installing a new green roof is just downright cool.  For you Extreme Makeover fans you might have seen me walking on the green roof in Piñon, AZ in the 2007 Extreme Green Makeover Home Edition (installed in April 2007 and shown on TV in September 2007).  I was also in Orlando, FL this past year on an installation that included a pet park on the seventh floor of a condo parking garage – a place for residents to take their pets for a pit stop without having to go to the street level.

Placement of the Green Roof Blocks on the steep roof of the Yazzie residence in the hot Arizona desert sun; Photos courtesy Kelly Luckett

However, while these two installations were challenging and interesting and very cool, they don’t hold a candle to the green roof installation in the great, frozen north (Chicago) that I attended in December 2006.  During the spring and summer of 2006, I kept hearing (in passing) Vic Jost of Jost Greenhouses asking Kelly Luckett of Green Roof Blocks™ when the Bank of America green roof was to be installed.  Initially I had no knowledge of the project location and my consultation was not needed as both Kelly and Vic had done green roof installs in Chicago before.  I knew from previous experience that I would be asked if help was needed.  I did learn that Vic was worried that if construction was delayed, the install of the Green Roof Blocks™ would either occur in late summer (in drought-like conditions) or, worse, in late fall/early winter when the green roof plants would not harden off. At G.R.E.E.N. we had already demonstrated on our research green roof that survival of green roof plants planted on the roof after mid-September had gone down precipitously.  In either case (late-summer or late fall/early winter install) in the Chicago project, the green roof plants may not survive, necessitating a replant (which is a disastrous outcome and expensive).  Turns out the construction delays were worse than expected, which led us to the “frozen” research experiment in which I participated.

A bit of technical history of the project to bring you up-to-speed:  The Bank of America that was to have the green roof was being built right next to the Dan Ryan Expressway in Chicago and was the first green roof on a Bank of America.  For the project, Green Roof Blocks™ were shipped to the Chicago area and planted (with a mix of Sedums) and held at Midwest Groundcovers by Grace Koehler (another of our collaborators) for the planned June, 2006 install, which due to construction delays, became August, then September, and then, finally, December.  Which brings me (and green roof research) back into the picture – it was decided late in November that the Green Roof Blocks™ being held at Midwest Groundcovers had “hardened off” enough and that the install would go ahead in December as planned.  IF the plants survived, then our “research” would tell us that installation of pre-planted, well established, properly hardened-off modular green roof systems would be an install option in the future if there was no other available.  In contrast, if the install was a failure (plant survival was compromised), then we would have learned this from our “research” experiment, too, and we would go back and replant with new knowledge (to avoid any late-season install).

Vic, Kelly and Mike Crowell (Kelly’s partner in Green Roof Blocks™) got together and a date was set for the delivery by Midwest Groundcovers and placement of the Green Roof Blocks™ on the Bank of America building for December 9, 2006.  So about 2 am on Saturday, December 9th, I was picked up at a commuter lot near my home in the St. Louis area and whisked up I-55 to Chicago with a team from Green Roof Blocks™ for the install.  WOW – what a learning (and cold) experience this trip turned out to be.

 Here you see the shingle conveyer in the parking lot with the “frozen” racks about ready to begin the lift to the roof – note the snow covered Green Roof Blocks™.

First, after about 3 hours in the vehicle we stopped at a gas station along I-55 and it was 2° F when we got out of the truck (bitterly cold). It was not much better when we arrived in Chicago at the install site (5° F at arrival and a balmy 7° F when we left in the late afternoon).  Second, it had snowed 8 inches in Chicago at the Bank of America earlier in the week and the roof was shoveled off by the construction crew on Friday in advance of our Saturday arrival when the sun finally appeared.  It had also snowed at Midwest Groundcovers and the Green Roof Blocks™ on top of the nursery racks still had snow on them when delivered (see picture above of the shingle conveyer and the partial green roof below to verify).  The snow-covered Green Roof ICE Blocks™ were heavier than the Green Roof Blocks™ on the lower shelves (with no snow cover) and a great competition was held to not have to handle the snow-covered Green Roof Blocks™.  Nevertheless, about 7:30 am on Saturday December 9th the install began.

Here you see some of the installed green roof (note the well established green roof plants) and Kelly and Vic snapping a line for the next section – note again the snow covered Green Roof Blocks™.

Once the install was completed, we packed up, climbed into the vehicles and thawed out all the way back to St. Louis.  Along the way, we discussed the probable outcome of our “research experiment.”  Once we got back to St. Louis, it was finals period for me and then Christmas Holidays and other green roof data analysis.  Reports filtered back from the GC that the roof was still “green” throughout the finish of the building – however, none of us had seen our handiwork post-install.  We were to get our chance at the grand opening of this Bank of America branch location – and by chance I was the only one able to go back to the site at this time.

The ribbon cutting followed a ceremony in which local school children and dignitaries spoke about green roofs.

So in May, 2007 I packed up my truck with some fertilizer, a hat (see in the picture above), and a digital camera and hustled back up to Chicago.  While there I participated in the ribbon-cutting, fertilized the green roof, assessed green roof plant survival (100% survival), and photographed the green roof for data purposes (validation for this article).  Kelly revisited the green roof in October, 2007 and reported 100% survival also.

Here you see the Branch Manager and her staff enjoying their new green roof atop the Chicago Bank of America – note again the lack of snow covered Green Roof Blocks™ in this picture!

PROJECT RESULTS
First, let me be clear that this “research project” reported above was not a planned, replicated research trial.  Those of us at G.R.E.E.N. would not conclude from a single project like this one that we have proven clearly our hypothesis “that green roof installation would consistently work in the dead of winter.”  However, as you can read in this report and see from the photos, this was (and continues to be) a successful green roof project and the “research” questions that were answered by this install are intriguing and valuable.  Some caveats:

1 – Growing out the Green Roof Blocks™ well in advance of the install and “hardening them off” in the field prior to the install contributed significantly to the overall success of the project.  We would recommend that you not try this with modular systems that were not established for almost an entire growing season.

2 – Even though it was bitterly cold for the crew that did the install, these conditions probably also contributed significantly to the success of the project.  If the green roof had been delivered during a time frame when the Green Roof Blocks™ were not frozen, the outcome may not have been as successful.

3 – While a great “research” project, I think my next install will be in sunny Florida!

4 – There were two accidents on the Dan Ryan next to the Bank while we were doing the install and another when I was fertilizing in May 2007.  Perhaps “the hat” is unlucky here, too?

Here you see some of the installed green roof in May 2007 and see the excellent plant growth – note the lack of snow covered Green Roof Blocks™ in this picture.

I am also happy to say in this edition of my research report that we are still monitoring many research projects and are beginning to plan for new studies to be initiated in 2008 in which we will be taking a critical look at the thermal benefits of green roof systems, native plant species, sloped green roofs and runoff water quality.  We have been collecting thermal data and runoff water quality from our field green roof experiments for about two years – we are reporting these results at the Green Roofs for Healthy Cities 6th annual Greening Rooftops for Sustainable Communities Conference in Baltimore this week (look for our SIUe talks and posters there).

As part of our ongoing projects, we have also begun to utilize bottom ash from the local Ameren power plant as experimental green roof growing medium.  We have also established a green wall research site and we are using green roof plants and are growing them in bottom ash, just like on our research green roofs in the green wall project.  We look forward to these new efforts and to reporting on our findings.

The great UnFROZEN Bank of America green roof project in October, 2007; Photo courtesy Kelly Luckett.

I’d like to again take a final moment at the end of this report to thank our industry collaborators (Green Roof Blocks™, Jost Greenhouses, Midwest Groundcovers, Midwest Trading Horticultural Supplies, Inc., JDR Enterprises, Inc., Emory Knoll Farms, Garick, Inc., Green Wall Ventures, and Greenroofs.com) – without them we would not be evaluating green roof technologies. Their contributions have been exceedingly generous and they are fantastic role models for our students.

I have never worked with a better group of students either – none of them has tried to push me off the roof and they tolerate my quirks and hat!  If you wish to join us in our quest for green roof knowledge, please contact us.  Thank you.

Bill Retzlaff, Ph.D.
Associate Professor
Chair, Department of Biological Sciences
Environmental Sciences Program
SIUe

Dr. Retzlaff has BS (Auburn University), MS (Auburn University) and Ph.D. (Clemson University) degrees in Forestry with a minor in plant physiology.  He has Post-Doctoral experience in Horticulture (Clemson University), Viticulture (UC Davis), and Environmental Sciences (Boyce Thompson Institute for Plant Research).  He also managed the commercial vineyards at Six Mile Creek Vineyards for six years while in Ithaca, New York.  Dr. Retzlaff has published in a variety of journals in forestry, air pollution, horticulture, and environmental issue areas.

Bill Retzlaff, Ph.D. is an Associate Professor in the Environmental Sciences Program, and Chair, Department of Biological Sciences at Southern Illinois University Edwardsville and is currently the research coordinator of the St. Louis metropolitan area research collaboration G.R.E.E.N. – Green Roof Environmental Evaluation Network.  G.R.E.E.N has been established to evaluate the performance of green roof technologies in the Midwestern United States.  "Our goal is to evaluate the performance of green roof technology and to make the information available to users for development/establishment of green roofs."

Dr. Retzlaff is The G.R.E.E.N. Editor here at Greenroofs.com, and contributes the bi-annual G.R.E.E.N. Research Report.  Reach Bill at:  Box 1651, SIUe, Edwardsville, IL 62026-1651; phone:  618.650.2728 or email him at:  wretzla@siue.edu.  Stay up to date at the website at:  www.green-siue.com and see the project in The Greenroof Projects Database.

The opinions expressed by our Contributing Editors may not necessarily reflect the beliefs of Greenroofs.com, and are offered to our readers to simply present individual views and experiences and open a dialogue of further discussion, debate and research across a wide spectrum of subjects within the greenroofing world.  Enjoy, and if you have a particular comment, please contact the author or send us an email to:  comments@greenroofs.com.


The G.R.E.E.N. Research Report
April 2007

By Dr. Bill Retzlaff, The G.R.E.E.N. Editor
All Photos and Graphs Courtesy Bill Retzlaff.

Dr. Bill Retzlaff

Dr. Bill Retzlaff

I’m Dr. Bill Retzlaff (above photo, in the “hat”) and I am the Coordinator of the Green Roof Environmental Evaluation Network (G.R.E.E.N.) located at Southern Illinois University Edwardsville (SIUe).  G.R.E.E.N. is a research cooperative between SIUe, Green Roof Blocks™, Jost Greenhouses, Midwest Groundcovers, Midwest Trading and Horticultural Supplies, JDR Enterprises, Emory Knoll Farms, Garick, The Gaia Institute, and Greenroofs.com that has been established to evaluate the performance of green roof technology in the Midwestern United States.

Faculty, Student Researchers, and Collaborators are working together to evaluate green roof performance and green roof technology and to make the information available to users for development/establishment of green roofs.  More detailed information about G.R.E.E.N. can be found at our web site (www.green-siue.com).

The primary goal of G.R.E.E.N. is to address issues of concern to the green roof industry in the Midwest and at other green roof locations nationwide using scientific (hypothesis-driven) research evaluations.  Our ancillary goal is to educate students (potential future industry leaders) about this emerging environmental technology by engaging them in green roof research. It is rare that classroom education is coupled with practical, hands-on experience with an emerging technology – our students hear and learn about green roof technologies in the classroom, then develop and implement their green roof experiments on the roof and in the field. In addition, each student’s research discoveries and outcomes help guide future research and industry directions in the development of green roofs.

In my last Greenroofs.com research report, I described our ground-level, fully replicated green roof storm water retention research trial.  I’d like to use this forum to report recent results from a U.S. EPA P3 (People, Prosperity, and Planet) Phase I research grant that G.R.E.E.N. received in September 2006.  The focus of this P3 project was three-fold: (1) to evaluate storm water runoff quality (nitrates); (2) to evaluate green roof thermal benefits; and (3) to evaluate atmospheric moisture loss from green roof systems.  My research collaborator on this project is Dr. Susan Morgan (Ph.D., P.E., Associate Professor in and the Graduate Program Director for the Department of Civil Engineering at SIUe) and she has contributed to this report.

Dr. Susan Morgan amongst the GreenPaks and Green Roof Blocks

Dr. Susan Morgan, Ph.D., P.E., Associate Professor in and the Graduate Program Director for the Department of Civil Engineering at SIUe.

Optimizing Green Roof Technologies in the Midwest

Our U.S. EPA P3 Phase I project had three objectives:
1. to determine the growing medium and plant species combination in ongoing green roof experiments that has the best water loss to the atmosphere following saturation (and, therefore, increase the storm water retention capacity of the green roof system);

2. to determine the concentration of nitrate being released from two green roof systems (built-in-place models and Green Roof Blocks™) compared to a conventional roof;

3. to determine the temperature of the roof surface (membrane) under three available green roof systems (built-in-place green roofs, Green Roof Blocks™, and Green Paks™) in order to evaluate the thermal benefits of green roofs.

Objective 1 – Atmospheric Storm Water Loss
Materials and Methods.  This portion of the research utilized two types of modular green roof systems—Green Paks™ and Green Roof Blocks™ — placed on the SIUe Engineering Building roof.  Both systems were filled with one of four types of growth media (Arkalyte, an expanded clay; Haydite, an expanded slate; lava rock; or Midwest Mix™).  Green Paks™ are each 2 ft x 3 ft x approximately 4 in. deep and were placed on a JDR drainage layer.  The drainage layer (JDR Drain) under each unit was placed with the 3/8 in. drainage cups either up or down to evaluate storm water retention by the drainage layer.  Half the Green Paks™ were planted with six Sedum kamtschaticum per pak.  Half the Green Paks™ were left unplanted.

Green Roof Blocks™ are 2 ft x 2 ft and are filled with growth media to a depth of 4 in.  Half the Green Roof Blocks™ were planted with five S. kamtschaticum plants per block, and the other half were left unplanted.

Both Green Roof Blocks™ and Green Paks™ were placed in a completely randomized design with three replicates.  After both green roof systems were in place, a garden hose with a sprinkler head was used to water each unit until it was completely saturated.  They were watered as needed over a 10-week period for plant establishment.

Water loss measurements with an Ohaus DS20L scale began in September 2006 after allowing time for the plants to establish and contribute to water retention and loss to the atmosphere. Weights of individual green roof modules were taken between 7:30 a.m. and 9:00 a.m. each weigh date.

The green roof systems were saturated using a hose and sprinkler head on September 13, 2006. Each system was then weighed on September 14. On September 17 approximately 2 inches of rain fell, saturating the media and filling the drainage layer in the “cups up” treatment.  The systems were weighed on September 18.  To allow time for evaporation and transpiration to occur, the systems were weighed next on September 20 and 21.

Results and Findings.  There was no difference in water loss among any of the unplanted green roof models (i.e., the growth media by itself had no impact).  However, there was a difference between the unplanted and the planted systems (which had plant coverage of only approximately 25%), indicating that the plants had an impact on water loss.

Similarly, no difference was found in the four growth media types among the planted Green Roof Blocks™ (Figure 1).  However, this result may have been influenced by the structure of the module (anodized aluminum bottom and sides).  Green Roof Blocks™ have drainage holes on their sides to allow excess water to escape, but the major evaporative surface is through the surface of the media unless fully covered by foliage.

Conversely, there is a difference in water loss between the planted Green Paks™ with different growth media (Figure 1).  Planted Green Paks™ with lava growth medium (80% lava and 20% composted pine bark) evaporated/evapotranspirated the greatest amount of water, about 25% more than the other media in Green Paks™ and about 50% more than any of the Green Roof Blocks™.  This green roof system is porous on all surfaces, which contributed to the greater water loss compared to Green Roof Blocks™.

Figure 1. Total water loss (evaporation/evapotranspiration) from planted green roof modules.¹

Green Roof Blocks™                                  Green Paks™

Total water loss (evaporation/evapotranspiration) from planted green roof modules

¹ Data collected between September 18 and 21, 2006.  Bars with different letters are significantly different (?<0.05). Error bars represent plus one standard error. (n = 3 for all)

There was also a difference in water loss between drainage layer orientation in the planted Green Paks™ system (Figure 2).  This difference is likely due to more water being retained with “cups up,” so there is more potential for evaporative water losses.  A significant question that remains regarding the drainage layer and water availability for the plants is that there is a root barrier between the “cups” of water and the Green Paks™.  The function of the root barrier is to prevent roof damage; it is not clear if water that evaporates then is available for plant use – a question for further study.

Figure 2. Total water loss from planted Green Paks™ with different drainage cup orientation.¹

Total water loss from planted Green Paks™ with different drainage cup orientation

¹ Data collected between September 18 and 21, 2006. Bars with different letters are significantly different (?<0.05).  Error bars represent plus one standard error. (n = 12 for both)

Objective 2 – Stormwater Quality Analysis
Materials and Methods.
  Collection of stormwater runoff was conducted at our green roof field site in two green roof stormwater retention studies (as described in previous research reports).  All green roof modules are planted with Sedum hybridum immergrauch.  Runoff is initially collected in gas cans from individual green roof models and control plots and then transferred to 250-mL plastic bottles, labeled, capped and refrigerated until lab analysis.  First flush and composite samples were collected from control roofs; composite samples were collected from the green roof models.

The first sample collection in the P3 study occurred on October 29, 2006 and was analyzed for nitrate and pH two times—on October 31 and November 2—to check for the effects of storage time.  A second sample collection occurred on November 16, 2006 and was analyzed for nitrate and pH on November 17, 2006.

All samples were analyzed using a Fisher Scientific Accumet XL25 pH/mV/Ion meter with combination nitrate ion electrode, pH electrode and temperature probe.  Standard methods outlined in the Fischer Scientific instruction manual for the Accumet XL25 meter were used for all analyses.  The meter was setup for ion operation in the “Direct Reading with Blank Offset” mode.  Required solutions, standardization, interferences, troubleshooting, and electrode care were referenced from the Accumet electrode instruction manuals.  An automatic temperature compensation (ATC) probe was connected to the meter and used to compensate for temperature variations in all analyses.  A magnetic stir bar and magnetic base was also used in all standards and samples during analysis.  Standardization of the XL25 meter for both nitrate and pH analyses was performed each day prior to analysis.

Sample preparation for nitrate analysis began with allowing the samples to acclimate to room temperature for 1 to 2 hours.  Then 100 mL of sample was added to a 250-mL beaker and the ionic strength was adjusted by adding 2 mL of 2 M (NH4)SO4 (a standard ionic strength adjuster).  Between measurements, glassware, stir bars and electrodes were rinsed with deionized water and dried.

Results and Findings.  Our results clearly indicate that nitrate levels in stormwater runoff, regardless of medium depth or type, are elevated above those of a control (conventional EPDM membrane) roof.  For the built-in-place green roof models using an 80% Arkalyte and 20% composted pine bark growing media, a shallow planted green roof medium depth of 5 cm leached the most nitrate (Figure 3).

There were large differences in nitrate leached from different growing media (generally 80% inorganic material and 20% composted pine bark) in Green Roof Blocks™ containing 10 cm of media (Figure 3).  The greatest concentration of nitrate in green roof stormwater runoff, which was more than twice the others, was leached from a commercial growing medium mix (rooflite™) donated by a collaborator (Figure 3).

Figure 3. Stormwater nitrate concentrations from control roofs and planted green roofs.¹ (Note the difference in nitrate scales.)

                   Built-in-Place                             10-cm Green Roof  Blocks™

Stormwater nitrate concentrations from control roofs and planted green roofs

¹ Values represent one sampling on November 17, 2006.  Bars with different letters are significantly different (?<0.05).  Error bars represent plus one standard error. (n = 4 for all)

Over 45% more nitrate leached from Green Roof Blocks™ containing 10-cm of Arkalyte growing medium than the built-in-place green roof model containing 10-cm of Arkalyte.  In fact, all the Green Roof Blocks™ containing 10-cm of growing medium leached more nitrate than all but the 5-cm built-in-place green roof.  This result may be attributable to the built-in-place models having more established plants, even though all the green roof systems had vigorous plant growth.  All had been fertilized with granular isobutylidene-diurea (IBDU, a water-released nitrogen fertilizer) that may be contributing to the nitrate concentration.  In any case more study is needed to evaluate seasonal differences, rainfall event differences, and whether the amount of nitrate decreases over time.

Objective 3 – Green Roof Thermal Characteristics
Materials and Methods.
  Hoboware thermal probes were placed underneath the growing medium of 12 green roof systems at the field site.  Each system used Arkalyte as the growing medium, with depths ranging from 5 to 20 cm.  Eight systems were planted with Sedum hybridum immergrauch and 4 systems were left unplanted.  The fertilizer used on planted systems was IBDU.  In addition, thermal probes were placed on two control (black membrane) roofs, and two probes monitored the air temperature.  All thermal probes were attached to Hoboware data loggers, which recorded temperatures every 15 minutes.  Data from the field site has been collected since August 5, 2005.

Results and Findings.  Results from our field site clearly indicate that the built-in-place green roofs studied will provide a thermal benefit to the roof membrane after installation.  Examining data from control roofs and green roofs with varying growing media depths (all 80% Arkalyte and 20% composted pine bark) in January 2006 indicated that the average monthly temperature of the roof membrane of the control roof models was at least 0.5° C colder than the same roof membrane under any green roof models (Figure 4).  Conversely, in August 2006, the average monthly temperature of the roof membrane of the control roof models was at least 3° C hotter than the same roof membrane under any of the green roof models in this study (Figure 4).

Note that these data are averaged over both day and night periods.  It is expected that the differences will be greater in a more detailed analysis, which will be done in the future.  In fact, the temperature under the green roof was less variable than on the conventional roof.  We are expanding our thermal evaluations this spring to many different planted/unplanted green roof systems to continue evaluating the thermal benefits of green roofs.

Figure 4. Mean monthly roof membrane temperatures from control roofs and planted built-in-place green roof systems. ¹ (Note the difference in temperature scales.)

     January 2006                                                 August 2006

Mean monthly roof membrane temperatures from control roofs and planted built-in-place green roof systems

¹  Values represent data collected at 15-minute intervals.  Bars with different letters are significantly different (?<0.05). Error bars represent plus one standard error. (n = 2976)

Conclusions and Recommendations
Based on the Phase I results, the following preliminary conclusions were drawn.  We will continue collecting and analyzing field data and revise them as needed.

From Objective 1
1. Weighing modular green roof systems can accurately determine water loss from evaporation and evapotranspiration.
2. Differences in water loss exist between two modular systems, between growing mediums in one modular system, and between drainage layer orientation.
3. Over time, the storm water retention capacity of green roof systems can be optimized by continuing the water loss monitoring efforts.

From Objective 2
1. The nitrate concentrations leaching from green roof systems with different growing medium depths and types were quantifiable.
2. Nitrate concentrations in runoff from green roof systems were greater than from control roof systems.
3. Over time, the nitrate concentrations leaching from green roof systems will likely decrease as plants become more established.  In addition, the concentrations can be reduced by utilizing different fertilizer types, different plants, and different growing medium types.

From Objective 3
1. The thermal benefits of green roof models at the ground-level field site compared to a standard control roof membrane in cold and hot months were quantifiable.
2. Green roofs reduced the temperature of the roof membrane in hot months and increased the temperature of the roof membrane in cold months.  In both cases, the temperature of the roof membrane under a green roof system is less variable than the roof membrane of a standard roof.
3. Over time, the characteristics of green roofs that will contribute to their thermal effectiveness—both for reducing the heat island effect and for reducing energy demand—can be characterized.  These characteristics may include the growing medium, plant species, and roof system.

Despite Phase I’s success, more work is needed to optimize the performance of green roofs, including the evaporation/evapotranspiration capabilities and the effects on stormwater quality. The research also needs to be expanded from flat roofs, which are primarily commercial applications, to sloped roofs for residential applications.  Additional verifiable data is still needed to develop models of the thermal effects of green roofs and the potential energy savings associated with installing green roofs.

NEW PROJECT
The green roof evaluations being conducted by G.R.E.E.N. are geared to provide municipalities, engineers, architects, contractors, building owners and other green roof users with guidelines for green roof installations that will tolerate the extreme summer and winter temperatures experienced on roofs in the Midwest.  All research studies are fully replicated scientific experiments that incorporate repeated evaluations over extended time periods to evaluate green roof performance using an established field site at ground-level and on the SIUe Engineering Building roof.

Phase I research from the EPA P3 grant funding focused on quantifying thermal effects, water loss, and nitrate releases from various green roof systems.  All the data that was collected was valuable for furthering the goals of the research and establishing these initiatives as long-term projects.  In addition Phase I results played an important role in determining the direction of a recent Phase II proposal – submitted on April 6th 2007.

Phase II will build on Phase I by modeling the thermal effects of green roofs and determining insulation values, or R-values, continuing to study the effects of green roofs with more established plants on stormwater quantity and quality (expanding the analysis from Phase I to include both nitrate and phosphorus), and expanding the research to sloped roofs (which represents adding the substantial residential market).

Based on interactions with engineering faculty through the course of Phase I, it was determined that two labor-intensive aspects of the research—collection of the evaporation/evapotranspiration data and the storm water runoff—could be automated through projects suitable for capstone senior design courses.  With successful completion of these projects in Phase II, significantly more data will be collected.  Please watch this space for additional research reports from these and new initiatives.

It goes without saying that we could not have conducted this valuable research and provided this report to the growing green roof industry without the generous grant funding to G.R.E.E.N. from the U.S. EPA P3 (People, Prosperity and Planet) research program.  Details about the U.S. EPA P3 program can be found at: (http://es.epa.gov/ncer/p3/fact_sheet.html).  Results reported (here and elsewhere) from this P3 funded study do not represent the views of the U.S. EPA, but have been reported to them as part of the contract agreement.  The contributions of Ms. Abby Wackerly (Environmental Sciences Graduate Student), Mr. Lane Richter (Biological Sciences Undergraduate Student), and Mr. Dave Richey (Chemistry Undergraduate Student) have been invaluable – they each contributed significantly to the research project.

I’d like to again take a final moment at the end of this report to thank our industry collaborators (Green Roof Blocks™, Jost Greenhouses, Midwest Groundcovers, Midwest Trading Horticultural Supplies, Inc., JDR Enterprises, Inc., Emory Knoll Farms, Garick, Inc., The Gaia Institute, and Greenroofs.com) – without them we would not be evaluating green roof technologies.  Their contributions have been exceedingly generous and they are fantastic role models for our students.

I have never worked with a better group of students either – none of them has tried to push me off the roof and they tolerate my quirks and hat!  If you wish to join us in our quest for green roof knowledge, please contact us.  Thank you.


Bill Retzlaff, Ph.D.
Associate Professor
Chair, Department of Biological Sciences
Environmental Sciences Program
SIUe
Box 1651 SIUE
Edwardsville, IL 62026-1651
618.650.2728


November 2006

By Dr. Bill Retzlaff, The G.R.E.E.N. Editor
All Photos and Graphs Courtesy Bill Retzlaff.

Dr. Bill Retzlaff

Dr. Bill Retzlaff

I’m Dr. Bill Retzlaff (above photo, in the “hat”) and I am the Coordinator of the Green Roof Environmental Evaluation Network (G.R.E.E.N.) located at SIUE.  G.R.E.E.N. is a research cooperative between Southern Illinois University Edwardsville (SIUE), Green Roof Blocks™, Jost Greenhouses, Midwest Groundcovers, Midwest Trading and Horticultural Supplies, JDR Enterprises, Emory Knoll Farms, Garick, and Greenroofs.com that has been established to evaluate the performance of green roof technology in the Midwestern United States.  Faculty, Student Researchers, and Collaborators are working together to evaluate green roof performance and green roof technology and to make the information available to users for development/establishment of green roofs.

More detailed information about G.R.E.E.N. can be found at our web site (www.green-siue.com). The primary goal of G.R.E.E.N. is to address issues of concern to the green roof industry in the Midwest and at other green roof locations nationwide using scientific (hypothesis-driven) research evaluations.  Our ancillary goal is to educate students (potential future industry leaders) about this emerging environmental technology by engaging them in green roof research.

It is rare that classroom education is coupled with practical, hands-on experience with an emerging technology – our students hear and learn about green roof technologies in the classroom, then develop and implement their green roof experiments on the roof and in the field. In addition, each student’s research discoveries and outcomes help guide future research and industry directions in the development of green roofs.  In my first Greenroofs.com research report, I described a ground-level, fully replicated green roof research trial with four growing medium depths (5, 10, 15, and 20 cm) and planted and non-planted green roof models.  I also reported that we had been monitoring storm water quantity in this research study by weighing collected storm water runoff after every rainfall event.  I reported that green roof models with plants retained 49-56%, without plants 47-49%, and control roofs 19% of incoming precipitation (storm water).  I’d like to use this forum again to report findings and conclusions from the first full year of the project (through one Midwestern fall, winter, spring, and summer).

One Year “On the Roof”: Evaluating green roof storm water runoff

To better understand the role of green roofs in storm water management, a study was initiated in September, 2005 to quantify the storm water runoff of green roof systems of varying growth medium depths (5, 10, 15, and 20 cm).  Thirty-two green roof models were constructed utilizing typical built-in-place technologies – ½ were planted with Sedum immergrauch and the other ½ were left unplanted.  The thirty-two green roof models and four (planted) Green Roof Blocks™ (modules) were fitted with individual flow-through storm water collection systems.  Only storm water that falls on the green roof models/modules enters the storm water collection system.  The experimental green roof systems were placed in a completely randomized experimental design with replicates of each medium depth and four control roofs with only EPDM roof surfaces.  Storm water runoff was collected from individual green roof models and quantified (weighed) after each of sixty-nine rainfall events over the course of the first project year.

PROJECT DESCRIPTION

Thirty-two green roof models and four (planted) Green Roof Blocks™ (modules) were fitted with individual flow-through storm water collection systems.  All thirty-two built-in-place green roof models are 70 cm x 70 cm wood frames with wafer board substrates, adhered EPDM roofing membrane, and JDR drain under the growth medium.  The models have sheet metal edging to retain the growth media (Figure 1).  All roof systems have been arranged so that only the precipitation that falls on the roof surface is collected in a storm water collection system.

Plant Species: Sedum immergrauch
Fertilizer: IBDU Nitrogen – a water activated fertilizer; plants fertilized 9/05 & 5/06
Growth Medium: blended arkalyte (expanded clay) – (80% arkalyte: 20% composted pine bark)
Irrigation: by hand for first two weeks after establishment – no irrigation after Sept. 19, 2005.

The SIUE Environmental Sciences Field Site

Figure 1. Green roof models with 5, 10, 15, and 20 cm growth medium depths, Green Roof Blocks™, and control roofs on tables at the SIUE Environmental Sciences Field Site.

Storm water runoff has been collected and weighed in the collection containers after each precipitation event (Figure 2) during the first year of the study.  The tare weight of each individual storm water collection container is then subtracted from the total weight (storm water + container) to determine net storm water runoff from each green roof model.  Once weighed, containers are emptied and reattached to the covered gutter system.  Two rain gauges are located on table three to quantify rainfall at the site.

A storm water collection container

Figure 2. Weighing a storm water collection container from one of the green roof models at the SIUE Environmental Sciences field site.

All recorded storm water data has been analyzed using SAS to determine whether or not there are differences in storm water retention among the different green roof systems (ANOVA for a completely randomized design, a < 0.05).

PROJECT RESULTS

It has rained at our field site sixty-nine times in the first year of the study – a total of 71.3 cm of precipitation has been recorded (approximately 25 cm below normal for our area).  In this time span, our control roof models (EPDM membrane only) have retained 19% of the precipitation while our built-in-place green roof systems of varying growing medium depths have retained more than 53% (Figure 3).  In general, the deeper the green roof medium, the more storm water retention.  However, in our study so far we have seen the most storm water retention in the 15 cm growth medium built-in-place models.  The additional 5 cm of growth medium depth in the 20 cm deep modules does not increase storm water retention.  In fact, while not statistically different, the storm water retention of the 20 cm growth medium built-in-place systems is less than that of the 15 cm modules.

Storm water runoff between 9/19/05 and 8/31/06 from green roof systems with 5, 10, 15, and 20 cm medium depths

Figure 3. Storm water runoff between 9/19/05 and 8/31/06 from green roof systems with 5, 10, 15, and 20 cm medium depths. Bars containing the same letter are not significantly different (a<0.05). (n=4 Control, n=4 Plants, n= 3 No plants). Error bars represent ± one standard error.

We also compared storm water runoff from built-in-place green roof models (planted and unplanted) containing 15 cm of growing medium with storm water retention of planted Green Roof Blocks™ (also with 15 cm of growing medium).  Storm water retention of built-in-place planted green roof models (61%) was greater than unplanted models (52%) and Green Roof Blocks™ (48%) (Figure 4).  We attribute the difference between the retention of the built-in-place models and the Green Roof Blocks™ to the presence of the JDR drainage material in the models and not in the Green Roof Blocks™.  Recall that the growth media depth is 15 cm, the growth media is the same aggregate blend, and that both model systems have the same square footage of roof surface area.  We do not feel that this is a negative attribute of the Green Roof Blocks™, but a positive aspect of the study – giving us a first indication of the retention capacity of the JDR drain material that we are evaluating.

Figure 4. Storm water from 9/19/05 through 8/31/06 of 10 cm green roof models and 10 cm Green Roof BlocksTM. Bars containing the same letter are not significantly different (a<0.05). (n=4 Control, n=4 Plants, n= 3 No plants, n=4 Green Roof BlocksTM). Error bars represent ± one standard error.

As this project moves into the second year and the green roof plants begin to completely cover the roof surface, we anticipate that there will likely be changes in the moisture retention of the planted green roof systems.  Through plant evapotranspiration we expect that the planted, covered modules will use more water – and therefore retain more storm water.  We will continue to monitor this aspect of the study and a future research report will detail our results.

NEW PROJECT

The project described above that we established last year to evaluate different growing medium depths and to compare built-in-place systems with modular green roof systems has provided valuable green roof storm water retention information.  We will continue this project and continue to evaluate results and to provide information to green roof users.  In order to expand our network and provide additional, beneficial information to green roof users, we have established a new green roof storm water retention evaluation alongside our original experiment.

Getting ready for the new monitoring study

New project set up.

 

New growing mediums

New aggregate growing mediums for study at SIUE.

In our new study, we are evaluating five different (Haydite, Arkalyte, Lava, Pumice, Recycled Glass, and HydRocks) blended (generally 80% aggregate: 20% composted pine bark) aggregate growing mediums in Green Roof Blocks™.

Sedum immergrauch

Sedum immergrauch.

In this study, there are five Green Roof Blocks™ of each growing medium – three planted (Sedum immergrauch) and two unplanted.

The new monitoring design.

The thirty Green Roof Blocks™ have been set in a completely randomized design on three tables.

Storm water retention studies for vaious blended growing mediums

An individual storm water collection system for each unit.

Each Green Roof Block™ has an individual storm water collection system and just like our initial study, we will be weighing the storm water that runs through each green roof model.  We expect to be able to report soon, with accuracy, the storm water retention of the various blended aggregate green roof mediums in this study – watch this spot on Greenroofs.com and our website for more details.

I am also happy to say in this edition of my research report that we are beginning to plan for new studies in which we will be taking a critical look at the thermal benefits of green roof systems. We have been collecting thermal data from our first field green roof experiment for about one year – I will report these results in another article soon.  Next year we are looking to expand our thermal evaluations and have begun to collaborate with Ameren (our local power company) to move this project forward.  As part of our ongoing projects, we have also begun to utilize bottom ash from the local Ameren power plant as experimental green roof growing medium.  We look forward to these new efforts and to reporting on our findings.

I’d like to again take a final moment at the end of this report to thank our industry collaborators (Green Roof Blocks™, Jost Greenhouses, Midwest Groundcovers, Midwest Trading Horticultural Supplies, Inc., JDR Enterprises, Inc., Emory Knoll Farms, Garick, Inc., and Greenroofs.com) – without them we would not be evaluating green roof technologies.  Their contributions have been exceedingly generous and they are fantastic role models for our students.  I have never worked with a better group of students either – none of them has tried to push me off the roof and they tolerate my quirks and hat!  If you wish to join us in our quest for green roof knowledge, please contact us.  Thank you.


Bill Retzlaff, Ph.D.
Associate Professor
Chair, Department of Biological Sciences
Environmental Sciences Program
Box 1651 SIUe
Edwardsville, IL 62026-1651
618.650.2728
wretzla@siue.edu


The G.R.E.E.N. Research Report
Inaugural Column, June 2006

By Dr. Bill Retzlaff, The G.R.E.E.N. Editor
All Photos Courtesy Bill Retzlaff unless otherwise noted.


Over the last eighteen months an exciting evolution has been occurring at Southern Illinois University Edwardsville (SIUE).  I have been privileged, along with my colleagues, our students and new industry collaborators, to establish the first green roof research site at SIUE – a research site that now is comprised of six Master’s thesis and six undergraduate student research projects.  We have made so much progress and several very significant discoveries to date that it is hard to know where to begin to describe the ongoing and new (it seems almost daily sometimes) research.

The Test Greenroof at Southern Illinois University Edwardsville;
May 26, 2006 Photo by Kelly Luckett.

I will be using my research column at Greenroofs.com to describe the scholarly efforts of a large group of individuals while we evaluate green roof technologies and address ways to improve green roof performance.  Thanks at the outset to Linda Velazquez and Greenroofs.com for providing me this opportunity to share our experiences and knowledge.  I am hopeful that my column will appear bi-monthly and detail our collaborative green roof research efforts AND significant green roof research discoveries/outcomes from other scientific studies.

Dr. Bill Retzlaff & Students

The Coordinator of G.R.E.E.N. (The Green Roof Environmental Evaluation Network) located at SIUE, and some very hard-working student researchers.


I’m Dr. Bill Retzlaff (photo, left – in the “hat”) and I am the Coordinator of the Green Roof Environmental Evaluation Network (G.R.E.E.N.) located at SIUE. G.R.E.E.N. is a research cooperative between SIUE faculty and students and green roof industry collaborators.  More detailed information about G.R.E.E.N. can be found at our web site, www.green-siue.com.  The primary goal of G.R.E.E.N. is to address issues of concern to the green roof industry in the Midwest and at other green roof locations nationwide using scientific (hypothesis-driven) research evaluations.

Our ancillary goal is to educate students (potential future industry leaders) about this emerging environmental technology by engaging them in green roof research. It is rare that classroom education is coupled with practical, hands-on experience with an emerging technology – our students hear and learn about green roof technologies in the classroom, then develop and implement their green roof experiments on the roof and in the field.  In addition, each student’s research discoveries and outcomes help guide future research and industry directions in the development of green roofs.

Presently, G.R.E.E.N. is comprised of three faculty, six graduate students, six undergraduate students, and five industry collaborators (Green Roof Blocks, Jost Greenhouses, Midwest Groundcovers, Midwest Trading and Horticultural Supplies, and JDR Enterprises).  Our group is committed to investigating the benefits and pitfalls of green roofs in a number of areas including: volume of storm water runoff from green roofs, green roof storm water quality, green roof plant growth, green roof plant performance, coverage of the roof surface by green roof plants, green roof thermal characteristics, green roof weight loads, energy benefits of green roof systems, and new green roof technologies.  We expect over the next several years to contribute to the science and discoveries that will permit this environmental industry to continue to expand.

The SIUE Environmental Sciences Program Field Facility at grade.

G.R.E.E.N. has established two green roof research locations at SIUE – one on the roof of the SIUE Engineering Building - now the location of five projects - and the other at grade (above photo) at the SIUE Environmental Sciences Program field facility.  We began our work at the field location in April 2005 with the construction of four large tables and thirty-six individual green roof models.  Our objectives at the field location (at grade, which facilitates easy handling of collected storm water runoff) are to quantify storm water quantity and quality as it passes through built-in-place and modular green roof systems.  We have established a fully replicated research trial with four growing medium depths (5, 10, 15, and 20 cm) and planted and non-planted green roof models.  We are also comparing 10 cm depth built-in-place green roof systems with 10 cm depth modular systems (Green Roof Blocks™).

The study also has four “control” roof models with an EPDM roof membrane surface only. The control roof models and their individual storm water collection system(s) allow for direct comparison with green roof storm water runoff of the various green roof models.  All green roof models contain Arkalyte growing medium and planted models are planted with Sedum hybridum ‘Immergrauch’ – five plants per model.  After resolving the roof leaks and testing the collection system (more detail in a future article), we have been monitoring storm water quantity by weighing collected storm water runoff after every rainfall event (fifty-five times since Sept. 5, 2005).  Results (find more at www.green-siue.com) over this period indicate that green roof models with plants retain 49-56%, without plants 47-49%, and control roofs retain 19% of incoming precipitation (storm water).  So far our maximum storm water retention (56%) has been in the 15 cm planted models.

As a second phase of the storm water study, we will soon place an additional thirty individual Green Roof Blocks™ (all in 10 cm of growing medium depth) with six different growing mediums (Arkalyte, Hadite, Pumice, Lava, Recycled Glass, and Midwest Mix) with individual storm water collection systems at the field location.  Our objective in this phase of the project is to evaluate which of six growing mediums retains the most storm water in a green roof system.  Watch for descriptions of this new project in future articles.

Phase I:  The SIUE Engineering Building roof.

The first G.R.E.E.N. roof experiment (above photo) was placed on the roof of the SIUE Engineering Building on July 20, 2005.  This project is an evaluation of different plant species (approximately 20 sedums and a couple of other non-sedums have been evaluated so far).  All plants in this study were placed in Green Roof Blocks™ containing a mixture of growing mediums.  Since the establishment of this roof-top study, we have been evaluating green roof plant growth, green roof plant performance, and coverage of the green roof modules.  One of our most significant findings to date is what we now consider to be a fertilizer injury incident.  Not too many weeks after establishment (mid-August 2005), ALL of the Sedum ‘Weinstephaner Gold’ on our green roof began to exhibit chlorosis (yellowing) and eventually perished – none of the other species in the study were affected in this manner.  We were very puzzled by this development and there were even rumblings from our collaborators about “students killing plants.”

Not too long after we observed the symptoms (and eventual death), a phone call came from green roof sites in Athens, GA and Columbia, MO with the same symptoms in the same species – S. ‘Weinstephaner Gold’.  The common denominator, besides the common sedum, was the use of Scott’s Osmocote fertilizer and a VERY slight precipitation event (less than 2 mm) at each site.  We hypothesize that the fertilizer was released, not flushed from the system properly, and excess fertilizer “burned” the ‘Weinstephaner Gold’.  The outcome of our “discovery” is a new study on the Engineering Building roof of 108 Green Roof Blocks™ (below) with three sedum species (S. hybridum ‘Immergrauch’, S. sexangulare, and S. spurium), three fertilizer treatments (Osmocote, IBDU, and NO fertilizer), and four growth mediums.

September 20, 2005; Photo by Kelly Luckett

Phase II:  We are looking at four media formulation; expanded slate, expanded clay, red lava rock, and white pumice. We are also looking at three species of sedum: S. spurium, S. sexangulare, and S. 'Immergrauch.'  Photo by Kelly Luckett.

This new “fertilizer” study was established on the Engineering Building roof on September 20, 2005 and we have been monitoring green roof plant growth, green roof plant performance, and roof coverage monthly to date in this project.  The green roof on the Engineering Building is entirely in the shade (you can see the shade line in July in the photo above) from approximately December 1, 2005 through February 28, 2006 – and incidental light is the plant’s only light source during this period.  As the roof of many other urban buildings are also in the shade for some time period each day or period of the year we were not too concerned about the location of our green roof project.  The full coverage three-story windows which permitted viewing of the project and the easy roof access moved the selection of the site forward (and the white safety rail helped too!).

Finally, we are looking at three fertilizing options; Osmocote, IBDU, and no fertilizer at all. There are three replications of each combination for a total of 108 Blocks. The Blocks have been randomized to eliminate any positional bias. The students are evaluating growth rate, saturation levels, leaching, and soil temperatures.  Photos by Kelly Luckett.

However, one of the three sedum species (S. hybridum ‘Immergrauch’) did NOT survive the winter on the roof, while out at our field site in the same models, same growing medium, and planted at approximately the same date, S. hybridum ‘Immergrauch’ plants survived and thrived.  Concerns were raised about plant health at establishment, a rapid freeze, and a host of other issues.  There was no interaction between species and growing medium or fertilizer – 100% of the S. hybridum ‘Immergrauch’ on the roof did not survive.  Very puzzling to say the least.  However, a chance comment to me by one of our collaborators (Grace Koehler of Midwest Groundcovers) about green roofs in Chicago under snow for extended periods (more than several weeks, no light, poor survival) and a chance planting of S. hybridum ‘Immergrauch’ at another offsite location that was also covered (shaded) has clued us in to what happened.  No direct sunlight during the winter equals NO survival of S. hybridum ‘Immergrauch’ here in our area.  We are now testing some additional sedums in the full-shade year round on our roof to identify a solution to this problem (more on this project in a later article).

September 20, 2005:  Student researcher volunteers and the test blocks.  Photos Kelly Luckett.

We have made much progress in the last eighteen months and research results are coming in daily.  We have assimilated so much information that we are hosting a Green Roof Symposium on Friday June 30, 2006 at SIUE (details at www.green-siue.com/symposium).  We hope to see you there.  In the last two months we have also placed three new projects on the SIUE Engineering Building – a shading (light) evaluation, a replicated trial of 120 Green Paks™ (a new modular product from Green Roof Blocks) containing four different growing mediums, and an exciting new study in which we are going to weigh daily individual modular green roof systems to calculate evaporation and evapotranspiration water losses – watch our roof and stay tuned for details.

I’d like to take a final moment in this first report to thank our industry collaborators (Green Roof Blocks, Jost Greenhouses, Midwest Groundcovers, Midwest Trading and Horticultural Supplies, and JDR Enterprises) – without whose involvement we would not be conducting our green roof experiments.  Their contributions have been exceedingly generous and they are fantastic role models for our students.  I have never worked with a better group of students either – none of them has tried to push me off the roof and they even tolerate my quirks and hat!  If you wish to join us in our quest for green roof knowledge, please contact us.  Thank you.


Bill Retzlaff, Ph.D.
Associate Professor
Chair, Department of Biological Sciences
Environmental Sciences Program
Box 1651 SIUE
Edwardsville, IL 62026-1651
618.650.2728
wretzla@siue.edu

 

 

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