A New Blue-Green Roof Solution: LiveRoof RoofBlue® RETAIN™
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Understanding the performance characteristics of new products in the green roof industry requires research. In 2021, Bradley Rowe, PhD and Kristin Getter, PhD conducted a full-scale peer-reviewed study on stormwater runoff mitigation testing various soil profiles, with and without mineral wool, and with and without the new LiveRoof Blue-Green Roof Assembly, called RoofBlue® RETAIN™ (Read the study here).
That study showed that RoofBlue RETAIN combined with the LiveRoof Planted Module assemblies reduced stormwater runoff an average of 82 percent during the test period. More specifically, during heavy rain events, the use of RoofBlue RETAIN underneath the lite module increased stormwater retention by 37.9 per cent, and 29.4 per cent under the standard module.
To follow up on the original research, we wanted to quantify how the RoofBlue RETAIN green roof assembly might impact plant growth and irrigation water conservation. But by then, Dr. Rowe had retired, and Dr. Getter had moved on to other things. So, we decided to undertake a simple, in-house, relatively low-cost scientific study on the performance benefits of this new product ourselves. From this research we have produced a White Paper entitled, “A Blue-Green roof enhances plant growth and reduces irrigation requirements.”
While this White Paper does not have the same degree of scientific rigor as the peer-reviewed research conducted by Dr. Rowe and Dr. Getter, it represents a valuable resource that can be used by architects, landscape architects, engineers, facility managers, and policy influencers to better understand the merits of this new blue-green roofing system. The method and findings of our research are summarized below, and in the full White Paper.
LiveRoof’s New RoofBlue® RETAIN™ Enhances Plant Growth and Conserves Irrigation Water … But, Just How Much?
LiveRoof’s RoofBlue® RETAIN™ in conjunction with LiveRoof’s Hybrid Standard Planted Green Roof Module. Excess water is stored in compartments below and made available to the plants at their roots through a wicking system – the RoofWick™. Photo:LiveRoof Global LLC.
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Many people are aware that stormwater discharge is an ecological and economic problem, and that stormwater retention by green roof systems presents many additional benefits to municipalities. As a result of its stormwater retention benefits, many municipalities have embraced green roofs as a compliance method through their stormwater codes. But these codes can sometimes mandate retention standards that exceed what can be accomplished with soil (growing media) alone. This in turn leads to novel ways of boosting water retention, beyond a growing medium’s ability to hold water. But if not done correctly, this can compromise plant health, green roof function and longevity, and add life cycle costs.
As biologists and horticulturists, we are acutely aware that green roof plants require a growing medium that is well-oxygenated, and neither too dry nor too wet, in order to be healthy and sustainable. Therefore, any additional stormwater retention beyond the growing media’s water holding capacity must be designed in a manner to avoid over-saturation. Over-saturated growing media causes oxygen depletion in the root zone of plants, and triggers root-rot diseases which compromise plant health and longevity. This is particularly true of sedums, a family of succulent plants commonly used in extensive green roof systems.
As stated previously, to better understand the water conservation and plant health performance of the new blue-green roof assembly, RoofBlue RETAIN, we decided to conduct our own research. In April 2022, we designed a study with twelve treatments containing 24 modules, each planted with the same type, arrangement, and quantity of plants—appropriate for each growing medium profile (depth). For example, the 2 ½” depth modules contained 2 Alliums each and a mixture of sedum cuttings, the 4 ¼” profile contained 2 accent plants (forbs/grasses) and a mixture of sedum cuttings, and the 6” profile contained 2 accent plants (forbs/grasses) and a mixture of sedums.
Plots were documented photographically on the first of each month. Half of the plots were not irrigated during the study, and the other half were irrigated only when the plants showed signs of wilting at 8:00 AM. When wilting occurred, these plots were irrigated with an amount of water equal to the soil’s water holding capacity for that particular growing media profile. At the end of the study, the plants were harvested, washed clean of soil and weighed (fresh and dry weights).
Research Results
Standard module system, irrigated. Left side shows LiveRoof Module + RETAIN assembly plot, right side plot is LiveRoof module only. Photo: LiveRoof Global LLC.
Water Conservation Assessment: With the irrigated plots, the Module + RETAIN assemblies required 43-78 percent less irrigation water than the Module-Only plots, depending upon soil depth. We view this as substantial water savings, and attribute it to the capture of stormwater (via the RETAIN basin) and the upward wicking of the captured water via the RETAIN system’s RoofWick, to the root zone of the plants. Water captured in the RETAIN assembly does not run off the roof, but is transferred to the roots of the plants through the RoofWick.
Plant Growth Assessment: In terms of plant growth (biomass), our findings were as follows:
Accent plant growth (forbs/grasses) was 37-122 percent higher in the LiveRoof Module + RETAIN assemblies, compared to the module-only plots.
The sedum species grew 56.84 percent and 0.73 percent bigger in the LiveRoof Module + RETAIN assemblies in the 2 ½” and 4 ¼” soil profiles (respectively), compared to the module-only plots.
The sedum species weighed less in the irrigated 4 ¼” and 6” LiveRoof Module + RETAIN assemblies (-12.3% and -25.41% respectively), compared to the module-only plots.
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These findings indicate substantially improved initial plant growth with the blue-green assemblies, and we attribute this to consistency of water availability and the recycling of nutrients (from rain, irrigation water and soil humates) that otherwise might have been lost to runoff. In the case of the sedum-planted, 4 ¼” and 6” deep LiveRoof Module + RETAIN assemblies that showed less sedum growth, this was due to the sedums being crowded out by the non-sedum accent plants. In a biodiverse green roof planting, as was represented in these plots, this would be viewed as positive and intentional, as the sedums may be a living mulch that would eventually succumb to the taller forb/grass accent plants.
Summary
Performance research is vitally important in understanding the extent to which new technologies in the green roof industry function. Our in-house research, combined with the peer-reviewed research of Dr. Rowe and Dr. Getter demonstrate that there are multiple benefits to combining blue-green roof technologies. This research demonstrates that the new RoofBlue RETAIN technology represents a sustainable solution to accomplishing three important things simultaneously: Reducing Stormwater Runoff, Conserving Irrigation Water, and Enhancing Plant Growth. The use of a blue-green roof represents a lower cost solution for stormwater management when compared to installation costs of a cistern, and can potentially provide many additional benefits via the overlying plant life.
This video summarizes the whitepaper.
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Anna Droz has a PhD in Ecology, is a certified Green Roof Professional, and Strategic Educator with LiveRoof Global LLC. and LiveWall LLC.
Dena Baker is an Ecologist and Senior Product Developer with LiveRoof Global LLC.
David S. Mackenzie is a Horticulturist and the President of, LiveRoof Global LLC., LiveWall LLC., and Hortech Inc.
Watch the video about the RoofBlue RETAIN product.
For additional photos, tables, and details on our methods and plant mixes, please see here.
For more information, call 800-875-1392 or visit LiveRoof.com
