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Roofmeadow prides itself on its technical expertise and commitment to evidence-based design. Unfortunately, there’s just not enough evidence out there.

Before going any further, perhaps a few words about the importance of evidence-based design are in order. After all, the modern green roof industry is about 15 – 20 years old. If evidence-based design were so important, wouldn’t the evidence be everywhere and obvious by now?

Designs informed by performance data result in green roofs that are less likely to fail and that require fewer interventions. Why does this matter?

  1. Green roofs typically are a sizable investment, justifying designs that minimize costs associated with failure (e.g., leaks, plant death, compromised drainage).
  2. To comply with the federal Clean Water Act, some jurisdictions have approved green roofs as methods to keep stormwater out of the public sewer system and waterways. A failed green roof isn’t doing its job.

So, the hunt is on . . .  who is collecting evidence of that “secret sauce” that makes green roofs work and last for the long haul? Here are a few of our most respected favorites:

The Chicago Botanic Garden

While many botanic gardens have installed green roofs to support their own green roof performance studies, none rival the efforts of the Chicago Botanic Garden.  Landscape Architecture Magazine’s January 2015 issue (available in stores now) includes a feature article titled “This is A Test,” written by Roofmeadow’s own Lauren Mandel.  The article describes the Chicago Botanic Garden’s five-year plant evaluation study of native and non-native perennials, grasses, and Sedum, planted in varying green roof media depths within two green roof areas.  The botanic garden’s in-house scientists have been collecting data on cultural adaptability, disease and pests, winter hardiness and ornamental quality. The researchers will evaluate plant performance relative to media depth and compare results to the performance of the same plants on the surrounding ground plane. This research has been underway since 2009 and the findings will be released in May 2015 in the botanic garden’s forthcoming Plant Evaluation Note.

Tim Ressler and the January 2015 issue of LAM, which includes the feature article "This is a Test" by EAT UP author Lauren Mandel.

Tim Ressler and the January 2015 issue of LAM, which includes the feature article “This is a Test” by EAT UP author Lauren Mandel.

The University Contingent

Roofmeadow always has kept abreast of the groundbreaking green roof research conducted at Pennsylvania State University. The Lady Bird Johnson Wildflower Center, a research unit of The University of Texas, has been pioneering research on the design and plant palettes for hot-climate green roofs and is one of the founders of the SITES™ Rating System.  Other universities that have contributed mightily to North America’s collective green roof knowledgebase include Michigan State University, North Carolina State University, University of Toronto, Villanova University (stormwater management focus, mainly), University of Washington, University of Maryland, Stevens Institute of Technology, Portland State University, and Columbia University.

 Oh, and, uh, Roofmeadow, of course!

At Roofmeadow, we doggedly seek out collaboration opportunities to test our theories and hypotheses (we have to keep reminding ourselves that we aren’t a research institution)! Over the years, we’ve amassed an impressive research pedigree in our own right:

  • Collaborated on the instrumentation design and monitoring of the green roofs on Chicago Walmart Store No. 5402 (largest monitored green roof in the world) and Portland Walmart Store No. 5899
  • Collaborated with Geosyntec Inc. and SAP to monitor the performance benefits of logic-based water level controllers in base flood-irrigated turf green roofs
  • Developed and implemented an innovative monitoring strategy to measure stormwater performance and evapostranspiration rates on St. Joseph’s University Science Center (in collaboration with Villanova University)
  • Designed and installed prototypes for flat and sloped green roofs at the Euro American Nursery in Bonsall, CA that feature local mineral materials, regional succulents, and a low-rate basal capillary irrigation system
  • Designed and implemented an ultra-lightweight green roof system featuring ceramic media at the Cincinnati Museum Center
  • Developed in-house testing methods including a fabric puncture-resistance test that better reflects field conditions and a direct measurement of fabric capillary potential (the Ressler Index) to inform irrigation design
  • Examined the benefits of amending green roof media with carbohydrates (specifically molasses) to encourage micro-biological activity and promote plant health (in collaboration with Emory Knoll Farms)*
  • Designed and installed a prototype living wall based on a French model emphasizing woody perennials, to inform plant selection and media design for future full-scale installations
  • Collaborated with Diadem USA to conduct tests in the US of a first-of-its-kind fall arrest system that is imbedded in green roof cover and requires no structural attachments
  • Evaluated long-term effects of freeze-thaw cycling on green roof media by measuring the distribution of silt and clay in field samples
  • Developed field procedures to quantify media amounts required to achieve finished grades in terms of in-place field densities (in collaboration with Skyland USA)
  • Refining approaches to increase diversity to extensive green roof plant communities by over-seeding with native annuals and perennials (in collaboration with several institutions)

*Spoiler Alert: We could not demonstrate that the molasses improved plant performance.

Photo of a Lady Bird Johnson Wildflower Center green roof test  plot from the Center's website.

Photo of a Lady Bird Johnson Wildflower Center green roof test plot from the Center’s website.

Evidence-based design is in Roofmeadow’s DNA.  We will continue to explore questions that are important to improving green roof design.  We choose to remain critical of received knowledge until we test assertions for ourselves.  Roofmeadow has more experience with more types of green roof assemblies than any other American company and we welcome engagement from the outside as we work to improve the foundation of green roof design.

A Killdeer on the largest monitored green roof in the world, Walmart Store No. 5402.

A Killdeer on the largest monitored green roof in the world, Walmart Store No. 5402.

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