It wasn’t until 1982 when the FLL Green Roof Guidelines were published in Germany as the standard for green roof construction and maintenance in Europe. It took another eighteen years in April of 2000 for the American Society for Testing and Materials (now ASTM International) to establish the Green Roof Task Group within the E60 Committee on Sustainability. We as ASTM International members, began to develop vegetative green roof standards. Nine standards or guides related to green roofs were published, of which five were then improved and updated within the twenty years since inception. This article will review the standards and guides that include ESCS (Expanded Shale, Clay and Slate) as an amendment to the growing media or when applied as fill or drainage on vegetative green roof systems.
Serving on an ASTM committee can be like purgatory. Since little was explained explicitly about exactly what happens in purgatory, it was clear that some sort of suffering was expected. Well, if you read Dante’s Divine Comedy it is spelled out at least seven times. ASTM, however is a different kind of trial, it is by committee. Getting a standard written, then passing through main committee, and finally published, takes time, a lot of time, sometimes years, and years, and years. The ASTM International committees meet twice per year for a few hours to develop and review standards and guides.
The subcommittee E06.71 was reorganized as Committee E60 on Sustainability with the creation of the Green Roof Task Group headed up by the late Michael Gibbons. I joined ASTM in late 2002, and in early 2003 we as ASTM members, began to develop vegetative green roof standards. I remember early on when we debated for hours specifically on the term “green roof,” which I will explain later.
After our initial work and developing fourteen standards our group was shifted over to ASTM Technical Committee D08 which now has jurisdiction over the development of standards for roofing/waterproofing membranes and insulations. The reason for the shift was because some of the D08 existing standards would be helpful in the evaluation of membranes and insulation used in vegetative (green) roof systems. After my last participation with the updating of ASTM E2777-20 Standard Guide for Vegetative (Green) Roof Systems in February 2020, I called it quits after almost twenty years. I finally was lifted out of purgatory.
ASTM International Standards and Guides Related to Vegetative Green Roofs
The first roof garden in the U.S. to use expanded shale as one of the components in the growing media was the Kaiser Center in Oakland, CA, completed in 1960. This experiment with lava rock and expanded shale was used to reduce the weight of the mix. Before then organic potting mixes and sand were used as the growing media. The lava rock and expanded shale still remain on the roof today. In Germany, long before the Kaiser Center, especially for the shallower extensive sedum mixes, crushed clay roofing tiles were used as the mineral component to reduce weight and provide good drainage, a method that is still used today. LECA, the European brand of ESCS lightweight aggregate is the norm in green roof growing media. Typical green roof growing media today consists of 60% – 80% ESCS, 20% – 30% organic matter (compost), and when needed 10% -20% medium to coarse washed sand. (Osmundson 1999)
Following Germany’s lead, by the late 1980’s green roofs were becoming a “state of the art” building practice in the U.S. The only guideline available at the time was the German FLL Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau e.V., Guideline for the Planning, Execution and Upkeep of Green Roof Sites, latest version 2020. http://www.fll.de This document was a wealth of information though broad in its scope, it really only addressed growing media parameters that met the European and Mediterranean climates. The expansive regions of the U.S. has such diverse and harsh climates, applying one all-inclusive planting system was not practical or successful in every region. Another point, local building codes were not ready to adopt the new green roof technology without assurances and additional engineering load requirement testing standards. With the lack of industry standards, specifications and guidelines, ASTM subcommittee E06.71 was reorganized April 2000 as Committee E60 on Sustainability. From there the creation of the Green Roof Task Group, headed up by the late Michael Gibbons, was started and in 2003 work began on Work Item 575 with the objective to establish a procedure for the assessment of green roof systems that includes both technical requirements as well as considerations for sustainable development.
“There was a strong market need for substantive guidance. Also, there was a pretty good range of VGR technologies,” says Dru Meadows, principal at TheGreenTeam Inc., Tulsa, Okla., and E60 chairman. “It was a classic example of market need for performance standards and an excellent example of ASTM bringing together stakeholders to develop consensus documents.”
At the first 2003 meeting the term “green roof” was debated, though widely used in the industry, it had not yet been standardized and had been criticized as misleading. For example, in terms of environmental applications, “green” roofs could mean reflective roofs, roofs made of recycled materials, vegetated roofs, or any other sustainable type, or simply a roof painted green. After over an hour of debate, mostly by the roofing company representatives, it was tabled until the next meeting. A year later the term Vegetative (Green) Roof Systems was adopted. For this paper I will use the industry norm of Green Roof which we are assuming as being vegetated. (Enright 2013)
Of the seven published documents, two are test methods specifically developed for testing green roof media and drainage materials used in green roof systems. For engineering performance, other than nutrients, particle size distribution and organic matter content, soil testing methods for landscaping and agriculture are not applicable for the mechanics of “soils” utilized for green roofs. The parameters necessary for drainage and saturated weight as well as other factors are not the same as soil used at ground level. Detailed specifications should be written around tests to ensure compliance with the performance requirements. Below is a summary of each of four standards/guides that relate to the growing media or aggregate drainage material recommended for green roof applications.
ASTM E2399/E2399M-19 Standard Test Method For Maximum Media Density For Dead Load Analysis Of Vegetative (Green) Roof Systems
This test method, originally published in 2005 and modified the last time in 2019, is the most widely used for sample submittal before a growing media is approved by the architects, landscape architects or engineers. This test method covers a procedure for determining the maximum media density for purposes of estimating the maximum dead load for green roof assemblies. The method also provides a measure of the moisture content, the air-filled porosity, and the water permeability measured at the maximum media density. All necessary for safety and plant performance.
*Turf and Soil Diagnostics
|Photo Credit: Turf & Soil Diagnostics (Turfdiag.com)|
E2396/E2396M-19, Test Method for Saturated Water Permeability of Granular Drainage Media [Falling-Head Method] for Vegetative (Green) Roof Systems
This test method developed for labs covers a procedure for determining the water permeability of coarse granular materials used in the drainage layers of vegetative (green) roof systems. It addresses water permeability under the low-head conditions that typify horizontal flow (transmissivity) in green roof applications. This test method is suitable for coarse-grained materials with 100 % of the material retained on the U.S. #8 [2.25 mm] sieve. It is not suitable for finer-grained materials.
Example of test results for 3/8” – #4 ESCS
*Agricultural Analytical Services Laboratory, Penn State University
E2788/E2396M -18, Specification for Use of Expanded Shale, Clay and Slate (ESCS) as a Mineral Component in the Growing Media and the Drainage Layer for Vegetative (Green) Roof Systems
First published in 2011, then modified in 2018, this specification details the quality and gradation requirements for utilizing ESCS in green roof systems.
ESCS is a lightweight, ceramic material produced by expanding and vitrifying select shale, clay or slate in a rotary kiln. It is a highly porous and low-density material. The raw shale, clay or slate used to produce ESCS is fired in the kiln at temperatures exceeding 1000 C. As it exits the kiln the material is sterile, inert, and ceramic. Some crushing may be performed to facilitate final screening in a screening system. ESCS is generally neutral in pH although the pH can vary somewhat depending on the raw material and the fuel used for processing. The E2788 document gives the average weights per cubic foot, physical and chemical properties of ESCS as well as various gradations. Based on ASTM C330 for coarse aggregates and C331 for finer gradations, the average gradations of the aggregates are given in chart form. It provides the gradation ranges best suited for the drainage layer or as a component in the growing media blend. This guide allows the user to select the grade needed to meet performance standards for weight and permeability of the mix or use for drainage. The finer ESCS allows for more water retention and a higher bulk density, while the coarser aggregates provide a lighter media with higher permeability rates if needed. The modification of the ratios of organic matter and any addition of sand can be fine-tuned using ESCS for water retention, porosity, bulk density as well as pH and cation exchange capacity.
*Expanded Shale, Clay and Slate Institute
ASTM E2777-20 Standard Guide for Vegetative (Green) Roof Systems
The work on this standard guide started on the first day our group met back in 2003, the day of the “what is a green roof” discussion. After much debate, it was finally published in 2014 and then updated in 2020. It is the ASTM go-to “Everything You Wanted to Know About Green Roof’s But Were Afraid to Ask” document. It identifies the terminology, principles and concepts of a vegetative green roofs. This guide discusses technical requirements for vegetative (green) roof systems pertaining to the categories such as: plants, media, wind scour resistance, soil reinforcement, separation or filter layers, drain layers, water retention layers, protection layers, and root penetration barriers. The standard is something of a checklist, for example, about such project parameters as maintenance, performance and longevity. Sections about planting media detail the different requirements for intensive systems and extensive systems, as well as functional properties of the media.
The sections related to ESCS cover growing media and drainage under section 7.0 Technical Requirements, within six pages of the forty-three page document, from 7.3 Media to 7.3.3 Functional Properties of Granular Drainage Media. Topics include: classes of media, extensive or intensive systems. Functional Properties of the Planting Media such as mineral contents (including ESCS), nutrient retention (CEC), longevity, retained water, permeability and drainage, porosity, pH, salt content, organic matter content, density, depth, capillary potential and wind scour resistance. All of the above are affected by the quality and quantity of the ESCS. Alternatives to ESCS are mentioned such as diatomaceous earth, perlite, lava rock and pumice. It however does mention that natural soils such as loam with silt and clay and high organic soils should be avoided because clogging, degradation and increased weight potential. The rest of the document covers a soup to nuts green roof information compilation.
Other documents that were published by the group included:
E2400/E2400M-19 Standard Guide for Selection, Installation, and Maintenance of Plants for Vegetative (Green) Roof Systems
E2397/E2397M-19 Standard Practice for Determination Maximum Media Density For Dead Loads Associated with Vegetative (Green) Roof Systems
ASTM E2398/E2398M-19 Standard Test Method for Water Capture and Media Retention of Geocomposite Drain Layers for Vegetative (Green) Roof Systems
ASTM D8014-17 Standard Guide for Selection of Membranes Used in Vegetative Roofing Systems
Other important ASTM testing methods recommended for green roof growing media are:
ASTM F1632-03(2018) Standard Test Method for Particle Size Analysis and Sand Shape Grading of Golf Course Putting Green and Sports Field Rootzone Mixes, Method B
Organic Measurements (LOI at 500°C SM 2540 G)
ASTM C29/C29M-17a Standard Test Method for Bulk Density (“Unit Weight”) and Voids in Aggregate
ASTM F1815-11(2018) Standard Test Methods For Saturated Hydraulic Conductivity, Water Retention, Porosity, And Bulk Density Of Athletic Field Rootzones (modified)
ASTM D4972-19 Standard Test Methods for pH of Soils
1. Osmundson, Theodore, Roof Gardens: History, Design, and Construction. New York: W.W. Norton and
Company, Inc., 1999
2. Enright, Cicely, (2013) Green Roofs are Growing Standards Support Sustainability, Standardization News ASTM International, May/June 2013. https://sn.astm.org/
3. Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau e.V., Guideline for the Planning,
Execution and Upkeep of Green Roof Sites, Release 2002
4. ASTM International, https://www.astm.org/
To purchase copies of the cited standards go to https://www.astm.org/products-services/standards-and-publications.
By Chuck Friedrich, PLA, ASLA, GRP