ASTM E2777-20

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E2777 − 20
Standard Guide for
Vegetative (Green) Roof Systems
This standard is issued under the fixed designation E2777; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
1.1 This guide identifies terminology, principles, and fun-
mendations issued by the World Trade Organization Technical
damental concepts including those related to sustainability,
Barriers to Trade (TBT) Committee.
technical requirements of construction, and types of vegetative
(green) roof systems used on buildings.
2. Referenced Documents
1.2 The considerations for sustainable development relative 2,3
2.1 ASTM Standards:
to vegetative (green) roof systems are categorized as follows:
C88/C88M Test Method for Soundness of Aggregates by
environmental, social, and economic as consistent with Guide
Use of Sodium Sulfate or Magnesium Sulfate
E2432. (See Appendix X1.)
D1079 Terminology Relating to Roofing and Waterproofing
1.3 This guide discusses technical requirements for vegeta- D1987 TestMethodforBiologicalCloggingofGeotextileor
tive (green) roof systems pertaining to the following catego- Soil/Geotextile Filters
ries: plants, media, wind scour resistance, soil reinforcement, D2974 Test Methods for Moisture,Ash, and Organic Matter
separation or filter layers, drain layers, water retention layers, of Peat and Other Organic Soils
protection layers, and root penetration barriers. D3786/D3786M Test Method for Bursting Strength of Tex-
tile Fabrics—Diaphragm Bursting StrengthTester Method
1.4 This guide addresses intensive and extensive vegetative
D4354 Practice for Sampling of Geosynthetics and Rolled
(green) roof systems for roofs up to 15 % slope. Roofing/
Erosion Control Products (RECPs) for Testing
waterproofing membranes and insulation are key components
D4439 Terminology for Geosynthetics
of vegetative (green) roof systems, but technical requirements
D4491/D4491M Test Methods for Water Permeability of
regardingtheirroleinsuchroofsystemsisbeyondthescopeof
Geotextiles by Permittivity
this guide.
D4595 Test Method for Tensile Properties of Geotextiles by
NOTE 1—ASTM Technical Committees D08 and C16 have jurisdiction
the Wide-Width Strip Method
over the development of standards for roofing/waterproofing membranes
and insulations, respectively. Some of their existing standards may be
D4716/D4716M Test Method for Determining the (In-plane)
helpful in the evaluation of membranes and insulation used in vegetative
Flow Rate per Unit Width and Hydraulic Transmissivity
(green) roof systems.As these two committees develop standards for such
of a Geosynthetic Using a Constant Head
roofs, this guide will be revised appropriately.
D4751 Test Methods for Determining Apparent Opening
1.5 The values stated in inch-pound units are to be regarded
Size of a Geotextile
as standard. The values given in parentheses are mathematical
D4759 Practice for Determining the Specification Confor-
conversions to SI units that are provided for information only
mance of Geosynthetics
and are not considered standard.
D4873/D4873M Guide for Identification, Storage, and Han-
1.6 This standard does not purport to address all of the
dling of Geosynthetic Rolls and Samples
safety concerns, if any, associated with its use. It is the
D5262 Test Method for Evaluating the Unconfined Tension
responsibility of the user of this standard to establish appro-
Creep and Creep Rupture Behavior of Geosynthetics
priate safety, health, and environmental practices and deter-
D5617 Test Method for Multi-Axial Tension Test for Geo-
mine the applicability of regulatory limitations prior to use.
synthetics
1.7 This international standard was developed in accor-
D5818 Practice for Exposure and Retrieval of Samples to
dance with internationally recognized principles on standard-
Evaluate Installation Damage of Geosynthetics
1 2
This guide is under the jurisdiction of ASTM Committee D08 on Roofing and For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Waterproofing and is the direct responsibility of Subcommittee D08.24 on Sustain- contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
ability. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Feb. 1, 2020. Published February 2020. Originally the ASTM website.
approved in 2014. Last previous edition approved in 2014 as E2777 – 14. DOI: Whenever a specific version of a standard is not identified, the most recent
10.1520/E2777-20. edition of the standard shall apply.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2777 − 20
D6637/D6637M Test Method for Determining Tensile Prop- 3.1.2 For terms related to sustainability and buildings, refer
erties of Geogrids by the Single or Multi-Rib Tensile to Terminology E2114.
Method
3.1.3 Fortermsrelatedtoroofingandwaterproofing,referto
D7361 Test Method for Accelerated Compressive Creep of Terminology D1079.
Geosynthetic Materials Based on Time-Temperature Su-
3.2 Definitions of Terms Specific to This Standard:
perposition Using the Stepped Isothermal Method
3.2.1 apparent opening size (AOS), n—for a geotextile, a
D7492/D7492M Guide for Use of Drainage System Media
property which indicates the approximate largest particle that
with Waterproofing Systems
would effectively pass through the geotextile.
D7877 Guide for Electronic Methods for Detecting and
3.2.2 capillary potential, n—of geotextiles, a property that
Locating Leaks in Waterproof Membranes
indicates the ability of a geotextile to distribute moisture.
E108 Test Methods for Fire Tests of Roof Coverings
3.2.3 cation exchange capacity (CEC), n—the capacity of a
E136 TestMethodforAssessingCombustibilityofMaterials
soil to retain and exchange the cations of nutrients, defined as
Using a Vertical Tube Furnace at 750°C
the sum of exchangeable cations that a media can retain per
E631 Terminology of Building Constructions
unit weight (1).
E2114 Terminology for Sustainability Relative to the Perfor-
mance of Buildings
3.2.4 clogging, n—for geotextiles, the condition where soil
E2396/E2396M TestMethodforSaturatedWaterPermeabil-
particles move into and are retained in the openings of the
ity of Granular Drainage Media [Falling-Head Method]
fabric, thereby reducing the hydraulic conductivity.
for Vegetative (Green) Roof Systems
3.2.5 dead load, n—foravegetative(green)roofsystem,the
E2397/E2397M Practice for Determination of Dead Loads
weight of a mature vegetative (green) roof system from the
and Live Loads Associated with Vegetative (Green) Roof
structural deck up, following rainfall, during which retained
Systems
and captured water attain maximum levels.
E2398/E2398M Test Method for Water Capture and Media
3.2.6 drain layer, n—horizontallayer,includingoneormore
Retention of Geocomposite Drain Layers for Vegetative
discrete components, that has been specifically designed to
(Green) Roof Systems
convey water toward the roof deck drains, gutters, or scuppers.
E2399/E2399M Test Method for Maximum Media Density
for Dead Load Analysis of Vegetative (Green) Roof
3.2.6.1 Discussion—Drain layers may be simple, consisting
Systems
of a single component, or complex, combining multiple com-
E2400/E2400M Guide for Selection, Installation, and Main-
ponents including: geosynthetics, geocomposites, and coarse
tenance of Plants for Vegetative (Green) Roof Systems
mineral aggregate. See also geocomposite drain layer and
E2432 Guide for General Principles of Sustainability Rela-
granular drain layer.
tive to Buildings
3.2.7 eutrophication, n—the process by which bodies of
E2788/E2788M Specification for Use of Expanded Shale,
water or other aquatic systems become overly enriched with
Clay and Slate (ESCS) as a Mineral Component in the
minerals and other nutrients.
Growing Media and the Drainage Layer for Vegetative
3.2.8 evapotranspiration, n—the process by which water is
(Green) Roof Systems
4 released to the atmosphere by evaporation from the surface of
2.2 ASCE/SEI Standard:
media and plant foliage, and components of the vegetative
ASCE/SEI 7 Minimum Design Loads for Buildings and
(green) roof system.
Other Structures (latest edition)
2.3 ANSI/SPRI Standards:
3.2.8.1 Discussion—Potential evapotranspiration rates can
ANSI/SPRI RP-14 Wind Design Standard for Vegetative
be determined using local climatic data. Specific evapotrans-
Roofing Systems
piration rates may vary with plant type, plant foliage density,
ANSI/SPRI VF-1 External Fire Design Standard for Vegeta-
vegetative (green) roof media composition, and availability of
tive Roofs
irrigation.
2.4 CSA Standard:
3.2.9 extensive vegetative (green) roof system, n—a roof
CSAA123.24 Standard Test Method for Wind Resistance of
system that features plants that can be sustained in shallow
Modular Vegetated Roof Assembly
media layers (with 6 in. or less of growing media), and
typically utilizes non-woody, drought-tolerant herbs, grass,
3. Terminology
moss, and succulents.
3.1 Definitions:
3.2.10 gap-graded, adj—granular materials in which the
3.1.1 For terms related to building, refer to Terminology
particle size distribution curve is markedly discontinuous.
E631.
Mixtures containing particles of both large and small sizes, in
which particles of certain intermediate sizes are wholly or
4 substantially absent. See particle size distribution curve.
Available from American Society of Civil Engineers (ASCE), 1801 Alexander
Bell Dr., Reston, VA 20191, http://www.asce.org.
Available from Single Ply Roofing Industry (SPRI), 465 Waverley Oaks Road,
Suite 421, Waltham, MA 02452, http://www.spri.org.
6 7
Available from Canadian Standards Association (CSA), 178 Rexdale Blvd., The boldface numbers in parentheses refer to the list of references at the end of
Toronto, ON M9W 1R3, Canada, http://www.csagroup.org. this standard.
E2777 − 20
3.2.11 geocomposite, n—a product composed of two or 3.2.20.1 Discussion—The maximum media density applies
more materials, at least one of which is a geosynthetic. to drained conditions.
3.2.21 module, n—pre-manufactured unit containing some
3.2.12 geocomposite drain layer, n—drain layer composed
of the functional elements of a vegetative (green) roof system.
of a synthetic sheet, mat, or panel.
3.2.21.1 Discussion—Independent modules are designed to
3.2.12.1 Discussion—Geocomposite drain layers may in-
be placed adjacent, and sometimes linked to one another, in
clude absorptive drain mats whose principle function is
order to cover roof surfaces.
drainage, but which will also contribute to water retention.
3.2.22 open-graded, adj—granular materials that contain
Some geocomposite drain layers may incorporate reservoirs
relatively few fines in order to leave fairly large spaces
that will capture water. See also granular drain layer.
between particles when compacted. See particle size distribu-
3.2.13 geosynthetic, n—aplanarproductmanufacturedfrom
tion curve.
polymeric material used with soil, rock, earth, or other
3.2.23 organic matter, n—material in a soil or vegetative
geotechnical-engineering-related material as an integral part of
(green) roof media that volatilizes from a dry sample when
a vegetative (green) roof system (as described in Practice
heated in an oven to 824 °F (440 °C).
D4354, Practice D4759, Guide D4873/D4873M, Test Method
D5617, and Practice D5818).
3.2.24 particle size distribution curve, n—curve, based on
sieve and hydrometer analysis, that describes the relative
3.2.14 geotextile, n—any permeable textile used with
quantities of particles of different sizes in a mixture.
foundation, soil, rock, earth, or any other geotechnical-
engineering-related material as an integral part of a man-made
3.2.24.1 Discussion—For planting media, this descriptor is
project, structure, or system.
limited to the non-organic fraction.
3.2.25 permeability, n—see saturated water permeability.
3.2.14.1 Discussion—Geotextiles perform several functions
3.2.26 permittivity, n—of geotextiles, the volumetric flow
ingeotechnicalengineeringapplications,including:separation,
rate of water per unit cross-sectional area per unit head under
filtration, drainage, reinforcement, and protection.
laminar flow conditions, perpendicular to the plane of the
3.2.15 granular drainage media, n—coarse aggregate ap-
geotextile.
plied in a layer at the base of the vegetated vegetative (green)
roof system profile or filled into the upper face of a reservoir 3.2.27 phytotoxic, n—poisonous to plants.
sheet to provide a horizontal plane for free drainage of the
3.2.28 protection layer, n—any continuous layer that is
vegetative (green) roof system.
intended to protect the roofing/waterproofing membrane from
damage and which is placed in direct contact with the
3.2.16 granular drain layer, n—a drain layer composed
entirely of granular drainage media. roofing/waterproofing membrane.
3.2.17 hardscape, n—non-vegetated surfacing on vegetative
3.2.28.1 Discussion—Agents for damage may include
(green) roof systems.
abrasion, puncture, UV exposure, and temperature fluctuation.
3.2.17.1 Discussion—Hardscape is most often used in place
Protection layers may include additional layers of material (as
of soil at walkways, plazas, maintenance areas, or at staging recommended by the membrane manufacturer), coatings, geo-
areas for mechanical equipment and façade access.
synthetic materials, geotextiles, geocomposites, tiles, and in-
sulation.
3.2.18 hydraulic transmissivity, n—for a geosynthetic or
3.2.29 reservoir sheet, n—a shaped plastic membrane con-
geocomposite, the volumetric flow rate per unit width of
taining receptacles on its upper surface to capture and retain
specimenperunitgradientinadirectionparalleltotheplaneof
water.
the specimen; also referred to as in-plane flow and, for a
granular drainage media, saturated water permeability multi-
3.2.29.1 Discussion—In some vegetative (green) roof
plied by the layer thickness (as determined using Test Method
systems, these receptacles are filled with granular drainage
D4716/D4716M).
media.
3.2.30 root penetrability, n—of a geotextile, a property that
3.2.19 intensive vegetative (green) roof system, n—intensive
indicates the ease with which plant roots can penetrate a
vegetative (green) roof systems feature large perennial plants
geotextile.
or turf grass.
3.2.31 root penetration barrier, n—continuous layer incor-
3.2.19.1 Discussion—The use of large plants generally re-
porated in a vegetative (green) roof system to prevent damage
quiresmediathicknessesinexcessof6in.(15cm),andinmost
to the roofing/waterproofing membrane system caused by root
instances, irrigation. Intensive vegetative (green) roofs will
growth.
require levels of maintenance similar to onground gardens. See
3.2.32 root resistance, n—ability of component to prevent
also extensive vegetated (green) roof system.
penetration by roots as measured in a long-duration test that
3.2.20 maximum media density, n—the density of a granular
simulates field conditions (2).
drainage media or vegetative (green) roof media determined
after they have been subjected to a specific amount of 3.2.33 saturated water permeability, n—for vegetative
compaction and hydrated by immersion to simulate prolonged (green) roof media, the coefficient which when multiplied
exposure to both foot traffic and rainfall. times the hydraulic gradient yields the apparent velocity with
E2777 − 20
which water at 68 °F (20 °C) moves through a cross-section of building’s function/purpose. The design of the vegetative
fully submerged media. (green) roof system should be responsive to the project
objectives.
3.2.34 soundness, n—for granular drainage media, the ca-
pacity to resist freezing without fracturing. 5.2 Sustainability—Vegetative (green) roof systems should
improve the sustainability of a building, including
3.2.35 thermal capacitance, n—a property of a material that
environmental, social, and economic impacts. Appendix X1
determines how readily it absorbs and releases thermal energy
provides a review of potential contributions that vegetative
(3).
(green)roofsystemsmaymaketowardachievingsustainability
objectives.
3.2.35.1 Discussion—Heat capacity, or specific heat, is the
measure for thermal capacitance. Heat capacity of a material is
5.3 Design Considerations:
determined by measuring the increase in temperature that
5.3.1 Maintenance—All vegetative (green) roof systems
attends the addition of thermal energy. In vegetative (green)
shall be accompanied by a detailed written maintenance
roof systems, the material with the highest heat capacity is
procedures manual, provided by the design professional, veg-
usually water.
etative (green) roof installation company, or system manufac-
3.2.36 underflow, n—water derived from rainfall or irriga-
turer. Maintenance manuals should include instructions for
tion that percolates to the base of the vegetative (green) roof
operation of irrigation systems, where relevant, and directions
system profile and then flows horizontally through the drain
for proper weeding and fertilization. These documents should
layer toward roof discharge facilities such as area drains,
also include methods for recognizing and dealing with com-
scuppers, and gutters.
monly encountered problems, including: insect infestations,
weedinfestations,barespots,wetspots,orareaswithperennial
3.2.37 vegetated (green) roof covering, n—see vegetative
surface water ponding. Depending on the vegetative (green)
(green) roof system, defined in Terminology D1079.
roof system and site conditions, provisions for employing
3.2.38 vegetative (green) roof media, n—materials that ful-
temporary irrigation should also be addressed. Manuals should
fill the role that natural soil would fulfill in at-grade landscape.
alsoincludeinstructionsforinspectingexposedelementsofthe
roofing/waterproofing membrane system, most notably the
3.2.38.1 Discussion—To achieve specified requirements for
drains. Minimum requirements for site visitations should be
weight, drainage, fertility, saturated water permeability,
provided, including safety considerations for accessing rooftop
density, etc., vegetative (green) roof media is typically pre-
areas. When applying nutrients, the type and method of
pared as mixture of fine and coarse mineral aggregate, organic
fertilization should take into account the quality of stormwater
materials, and admixtures.
runoff. Fertilization procedures using nitrogen-based fertilizers
3.2.39 vegetative (green) roof system weight, n—see dead
shall also address mitigation of eutrophication.
load.
5.3.2 Performance—The design professional working on a
vegetative (green) roof system shall convey to the owner a
4. Significance and Use
written description of the system, showing conformance with
4.1 Intended Use—The intended use of this guide is to the specified performance characteristics. These descriptions
provide general information to practitioners in the fields of include at minimum: (1) maximum or minimum associated
vegetative (green) roof design and construction. The guide dead load, (2) moisture retention capacity per hydrology study
encourages innovative but responsible vegetative (green) roof by the manufacturer, (3) assurances of the longevity of the
design, with a focus on performance and quality assurance. vegetative (green) roof system, (4) assurances of the survival
Numerical ranges, practical minimums, and benchmarks that of the plant foliage cover, and (5) assurances that the roofing/
areincorporatedintheguideareintendedforreference.Design
waterproofing membrane is compatible with the selected veg-
requirements for specific projects vary and, therefore, qualified etative (green) roof system and suitable for the application.
professionals may prepare designs with features that may vary
Written descriptions of vegetative (green) roof system perfor-
from the recommendations contained in the guide. In all mance characteristics typically emanate from, and will be
instances,vegetative(green)roofsystemdesignsshallconform supported by, the manufacturer or provider of the vegetative
to the applicable code requirements of federal, state, (green) roof system.
provincial, or local agencies with jurisdiction.
5.3.3 Longevity—The longevity of vegetative (green) roof
systems can be limited by: (1) degradation or loss of function
4.2 Users—Users of this guide include: planners,
of components of the vegetative (green) roof system, or (2)
developers, architects, landscape architects, engineers, general
premature failure of the roofing/waterproofing membrane sys-
contractors, subcontractors, owners, facility managers, finan-
tem. Consideration should be given to locating leaks and
cial organizations related to building industry, building mate-
repairing the membrane. For novel designs or large-scale
rials and product manufacturers, government agencies includ-
projects, mock-ups of vegetative (green) roof systems may be
ing building officials, and other building professionals.
advisable. Exposed surfaces of the roofing/waterproofing
membrane system (for example, flashings and penetrations)
5. Principles Relative to Vegetative (Green) Roof Systems
may become the most important factor in determining the
5.1 Design Intent and Building Function—Vegetative longevity of an installation. Consideration should be given to
(green) roof systems should contribute or enhance, or both, a providing protection for all surfaces of the roofing/
E2777 − 20
waterproofing membrane system. For instance, flashings equipment, and adjacent to penthouse structures. Guidance on
should be protected with a durable and UV-resistant protection wind design for vegetative (green) roof systems can be found
layer or counterflashing.
in ANSI/SPRI RP-14. The potential for damage by wind will
vary with building height, building geometry, geographic
5.3.4 Structural Loads—The introduction of a vegetative
location, and local topography. The roofing system as a whole
(green) roof system to a new or existing structure has an effect
on the live, dead, and seismic loads. The addition of materials must resist wind uplift forces as required by code. In addition,
the vegetative (green) roof system must resist wind damage to
associated with vegetative (green) roof systems usually in-
creases the dead load in varying amounts based on the number, the exposed vegetative components, such as growth media
composition,andthicknessofthelayersofthesystem.Because beingscouredaway(specificallycoveredin7.4).Onvegetative
of the transient water retention capacity of vegetative (green) roofs that are properly designed and maintained such that
roof systems, the live loads may increase as well. In accessible vegetation cover increases with time, probability of wind
roofs, the live loads created by human occupants should be
damage to the exposed vegetative components is greatest with
taken into account. Minimum live load allowances for access high winds immediately after installation and diminishes as the
by pedestrians, as well as by maintenance personnel, apply in
vegetative (green) roof matures. Evaluation of the wind resis-
most jurisdictions. The additional dead and live load attribut-
tance of modular vegetative (green) roof systems (resistance to
abletothevegetative(green)roofalsocontributetotheseismic
wind uplift as well as resistance to wind flow) can be
mass of the building structure, substantially increasing the
performed using CAN/CSA A123.24. With many vegetative
horizontal seismic response, as well as affecting the fundamen-
(green) roof systems, methods for temporarily protecting the
tal period. Consideration of appropriate loads is the responsi-
media prior to establishment of a mature plant ground cover
bility of the design professional and shall be addressed before
may be advisable. This may include mats or mesh fabricated
the vegetative (green) roof system is designed.
from organic fibers or geosynthetics, tackifying agents, or the
5.3.4.1 Take into account all components in the vegetative
installation of pre-grown mats or modules. Various permanent
(green) roof system profile and include the weight of matured
stabilized leading-edge systems may be viable for a particular
plants and retained moisture.
project, including: gravel or stone margins, unit pavers,
5.3.5 RoofAccess—Building maintenance and other person- strapped or bolted pavers, reinforced media layers, and buried
nel shall be provided with a safe means of accessing the roof. ballasts in conjunction with reinforcing geotextiles. The width
of stabilized leading-edge systems depends on the local wind
5.3.6 Equipment Access—When mechanical equipment is
environment, which is specific to each building and geographic
located on the roof, accommodations shall be made to provide
setting. Measures shall comply with requirements of federal,
safeaccesstothatequipment.Determinationshallbemadethat
state, provincial, or local entities with jurisdiction. Methodolo-
the vegetative (green) roof system will not interfere with
gies for determining ballast requirements often rely on esti-
equipment operation. Allowances shall be made for required
mates of wind velocities and uplift pressures based on ASCE/
clearances for working around and under the equipment.
SEI 7. The dry weight should be used when evaluating the
Hardscape may be used in these spaces to provide working
ballast weight of a vegetative (green) roof system. In some
areas. Measures shall be included to prevent damage to the
jurisdictions upper limits on basic wind speed (3-s gusts) may
vegetative (green) roof system caused by wash-down, ‘blow-
down,’ or other discharges of fluids associated with operation apply to inclusion of gravel or stone ballast, due to the risk of
these becoming windborne missiles.
or maintenance of mechanical equipment. Chemicals used in
the operation or maintenance of mechanical equipment located
5.3.9 Fire Resistance—Just like any other roofing system,
in the field of a vegetative (green) roof system should not be
vegetative (green) roof systems must meet the fire classifica-
phytotoxic to any of the designated plant varieties or damaging
tion required by code. In that regard, guidance is provided in
to the components of the vegetative (green) roof system.
ANSI/SPRI VF-1. In regions where wildfires are an identified
5.3.7 Façade Access—In many instances, the roof serves as threat, it is recommended that designs emphasize foliage cover
the primary point of façade access. Consideration should be
consisting of succulent plants (for example, Sedum, Senecio,
given in vegetative (green) roof system design for access to Delosperma, Graptopetalum, Echeveria, etc.), and the vegeta-
façade rigging equipment, including the use of temporary
tive (green) roof system should be maintained to regularly
equipment (beams and weights). If walkways and staging areas remove dead or dormant grass and shrubs. Non-vegetated
for façade maintenance are not provided, damage to the
margins, consisting of coarse stone, gravel, concrete pavers, or
vegetative (green) roof system may result. Chemicals used for stone pavers can be used to set back foliage-covered areas.
window and façade cleaning and maintenance should be
Specifically, setbacks for plant foliage are recommended in the
reviewed prior to their use to determine if they are phytotoxic
following situations: (1) walls immediately beneath the sills of
and may inhibit plant growth in areas affected by façade
operable windows, and (2) adjacent to hatchways, thresholds,
maintenance. Materials that will be phytotoxic to plant variet-
andmechanicalequipment.Non-vegetatedsetbacksarerecom-
ies designated for the vegetated (green) roof system should be
mended for boundaries with roofing/waterproofing membrane
replaced by alternative materials that are benign toward these
systems that are not rated Class A, as determined by Test
plants.
Methods E108, and for building surfaces constructed using
5.3.8 Wind Resistance—Damage by wind is a concern with materials that have not been successfully tested in accordance
vegetative (green) roof system installations, particularly along with Test Method E136. For vegetative (green) roof systems
perimeters and corners, at obstructions such as mechanical that are not rated ClassAor B as determined by Test Methods
E2777 − 20
E108, additional precautions are recommended, including may lead to perennially stressed conditions for the plants and,
providing breaks in the vegetative (green) roof system that will in extreme conditions, plant mortality.
limit the area of any contiguous, foliage-covered roof zone.
5.3.13 Freeze-Thaw Cycling—Vegetative (green) roof
Breaks may consist of concrete or masonry curbs that are taller
systems, especially those with areas open to air below, can be
than adjacent plant foliage or non-vegetated strips. Non-
adversely affected by freeze-thaw cycling. In cold weather,
vegetated strips may consist of either: (1) coarse stone, gravel, water can percolate through the soil over an enclosed area until
concrete pavers, or stone pavers, or (2) roof covering rated itreachesanareawherethetemperaturedrops.Whenthewater
reaches the colder roof, it can refreeze and form a dam. This
Class A, as determined by Test Methods E108. All vegetative
prevents upstream water from being able to drain and in turn
(green) roof systems should be provided with access to hose
adds to the weight of the roof. To avoid this situation, roofs
bibs, faucets, or an irrigation system that can provide sufficient
over colder areas may require additional design loads or some
water to allow the entire vegetative (green) roof system to be
type of heating to keep water from freezing.
thoroughlysoakedwithinanelapsedtimeof2h.Provisionsfor
introducing fire-resistance measures shall comply with require- 5.3.14 Soil Creep—The growing media in vegetative
ments of federal, state, provincial, or local entities with (green) roof systems can, over time, redistribute its mass.
jurisdiction. Maintenance plans discussed in 5.3.1 should allow for periodic
inspections of the media, including depth sampling as well as
5.3.10 Flashing—To minimize the opportunity for water to
instructions for re-grading of the surface when the soil depths
gain entry through the roofing/waterproofing membrane
get beyond those for which they were designed.
system, minimum vertical isolation distances between the
upper surface of the vegetative (green) roof cover and the top
6. Quality Assurance
of the flashing is advised. These vertical isolation distances
may vary with manufacturer and flashing type; some manufac-
6.1 Specifications—Specifications should clearly define the
turers require a minimum vertical isolation of 8 in. Vegetative
performance requirements for the vegetative (green) roof
(green) roof system profile thicknesses must be adjusted
system, identify the relevant properties of constituent
accordingly. If the recommended vertical isolation distance
components, identify hazardous conditions, and include appro-
cannot be satisfied, then the vegetative (green) roof cover
priate procedures to monitor construction, provide a safe
should be set back from the flashing using rigid edging. working environment, and provide ongoing maintenance.
5.3.11 Leak Detection—Design of the vegetative (green) 6.1.1 Performance Requirements—Performance require-
roof system should include consideration of how leaks can be ments may vary. However, where vegetative (green) roof
systems have been selected with specific objectives in mind,
located and repaired. For example, compatibility of the
these should be included in the specification. Where specific
roofing/waterproofing membrane system and other compo-
energy conservation or stormwater control objectives are
nents of the vegetative (green) roof system with leak detection
important, civil engineering reports, supporting computations,
systems, as well as methods involving high and low-voltage
field data, or computer simulations should be required of
electrical methods of leak detection, should be determined.
providers of vegetative (green) roof systems.
Guidance on electric leak detection techniques can be found in
6.1.2 Submittals—Properties cited in specifications should
Guide D7877.
be relevant to the successful performance of the vegetative
5.3.12 Drainage—Vegetative (green) roof systems can be
(green) roof system. To the extent practical, specifications
adversely affected by either excessive or insufficient drainage
should provide ranges of acceptable performance, or design
capacity. The first concern of the designer when addressing
minimums and maximums.
drainage should be to ensure that the vegetative (green) roof
6.1.2.1 For materials and components that are unique to
system can efficiently percolate and discharge the underflow
vegetative (green) roofs, contractors should provide certifica-
associated with mandated design storms. Unless specifically
tions by manufacturers that any tests have been successfully
designed to generate surface runoff, vegetative (green) roofs
performedbyanindependentlaboratoryandthattheirproducts
systems should not experience ponding or surface flow when
comply with the specification.
subjected to rainfall events that would be normal for a typical
6.1.2.2 For vegetative (green) roof media, samples should
year. Prior to installation of overburden materials, the com-
be accompanied by certified statements by the manufacturer/
pleted roofing membrane should be inspected to confirm
blender—or recent tests by an independent laboratory—
satisfactory drainage conditions of the roofing system. All
demonstrating compliance with the specifications. Since the
drains and scuppers should be isolated by a filter fabric, or
characteristics of feed stocks such as ESCS and compost may
other appropriate means, to protect from clogging caused by
vary over time, tests for specific media formulations should be
the accumulation of foliage or debris. Conventional ‘beehive’
conducted on a periodic basis.
or‘bonnet’strainersarenotsuitableforthispurpose.Chambers
6.1.3 Maintenance Program—Contract documents should
with removable lids are recommended for use at all drains and
be specific concerning the maintenance requirements and
scuppers. Surrounding all drains and scuppers and along
responsibilities of the vegetative (green) roof system installer
depressions where underflow concentrates, coarse stone aggre-
or system manufacturer. For example:
gate should be placed to facilitate percolation and horizontal
flow toward the drainage facilities. The designer should avoid
6.1.3.1 Procedures for leak detection and repair, as
excessive drainage of the vegetative (green) roof system which necessary, for the roofing/waterproofing membrane.
E2777 − 20
6.1.3.2 Requirements for minimum foliage cover prior to planting media that incorporate lightweight mineral aggregates
acceptance by the owner. Specify remedies if the cover as their principal constituent. Vegetative (green) roof planting
requirement is not satisfied at the end of the designated
media should exhibit a well-graded character. Gap-graded
establishment period. materials are not recommended for use as planting mixtures, as
6.1.3.3 Requirements for continued performance, including
thesetendtoseparateandlosesaturatedhydraulicpermeability
effective drainage, soil thickness, horticultural viability, etc., over time. In order to minimize the potential for compression
provided the maintenance program is followed.
over time, vegetative (green) roof planting media should
6.1.4 Required longevity for constituent components. contain a more or less continuous range of particle sizes that
imparts a stable structure to the media layer. The choice of
6.2 Project Check List—The following project check list
which ingredients to use in a planting mixture may depend on
includes recommended activities to achieve successful out-
factors such as: performance specification, regional
comes with vegetative (green) roof system installations.
availability, cost, and allowable dead load. Most mineral
6.2.1 Determine the project’s priorities, including sustain-
aggregates are provided in many gradations. The grain-size
ability goals.
distribution curve for the mineral fraction should be selected
6.2.2 Determine dead load and live load allowances.
with the goal of providing sufficient pore space for air, water,
6.2.3 Evaluate regional climate and microclimatic condi-
and the exchange of gases. Mixes with finer particles generally
tions.
have higher surface areas and smaller pores, which enhance
6.2.4 Select vegetative (green) roof system(s) that can best
water retention capacity and capillarity of the planting mixture.
achieve project priorities.
However,toomanyfineparticlesmayleadtocloggingandloss
6.2.5 Coordinate vegetative (green) roof system details and
of drainage properties over time. The silt-size fraction (mate-
requirements with the roofing/waterproofing membrane system
rial passing the No. 200 U.S. sieve (0.075 mm)) should be
manufacturer.
closelymonitored,sinceexcessivequantitiesofsiltmayleadto
6.2.6 Prepare detailed specifications and address whether all
clogging of fabrics and stratification of the media. Under most
components (membrane up to and including plantings) should
circumstances the silt content of media should not exceed
be furnished by one manufacturer, or that the responsibility for
15 %. Clay-size material should be avoided, except as top-
same rest in one contractor.
dressing in some intensive vegetative (green) roof systems. In
6.2.7 Implementation:
general, planting mixtures require a blend of different sizes and
6.2.7.1 Maintainthecompletedroofing/waterproofingmem-
types of mineral ingredients. Natural topsoil should be used
brane system in a protected condition.
with caution, due to their clay and silt content, as well as the
6.2.7.2 Consider testing delivered vegetative (green) roof
potential burden of unwanted seeds, rhizomes, and potential
media in order to confirm compliance with the specification.
pathogen inoculation. Natural soils are prone to compaction
6.2.7.3 Monitor vegetative (green) roof system installation.
wheninstalledinthinlayersaspartofavegetative(green)roof
6.2.7.4 Document vegetative (green) roof system perfor-
system. Sandy loam soils may be suitable as amendments for
mance during the establishment period (typically two to three
some intensive planting mixtures. In anticipation of thinning of
years are required for a vegetative (green) roof system to attain
the media over time due to compaction and winnowing by
a stable condition).
wind, it is advisable to place the media with an initial thickness
6.2.7.5 Conductregularongoingmaintenance,asdirectedin
that is 10 to 20 % thicker than the specified thickness, after
the maintenance program, and document activities to the
moistening and rolling.
owner.
7.3.1 Classes of the Planting Media:
7. Technical Requirements 7.3.1.1 Planting Media for Intensive Roof Systems—
Intensive systems have deeper media layers, typically ranging
7.1 Thissectionaddressestechnicalrequirementsassociated
from 6 to 48 in. (15 to 120 cm). Relative to extensive planting
with plants, media, wind scour resistance, soil reinforcement,
mixtures, intensive planting mixtures are generally character-
separation or filter layers, drain layers, water retention layers,
ized by finer particle sizes, lower air-filled porosity, lower
protection layers, root penetration barriers, and membranes.
saturated water permeability, and higher water retention ca-
7.2 Plants—Refer to Guide E2400/E2400M.
pacities.Intensivevegetative(green)roofsystemsaredesigned
to support a wide variety of plants. Depending on the cultural
7.3 Media—Detailed specifications should be written
requirements of the plants, the planting media may vary with
around tests that can be conducted on samples of the final
respect to pH, saturated water permeability, moisture retention
planting mixture. To ensure compliance with the performance
requirements, testing of the final mixture should be considered. capacity, organic content, etc. As a general observation, ongo-
ing addition of amendments to intensive vegetative (green)
The purpose of the planting media is to sustain the life of the
plants over an extended period of time, function as a moisture roof systems as part of the maintenance program are suggested
to ensure optimum growing conditions. The type of plants that
reservoir, support efficient drainage during rainfall events, and
protect the underlying components of the vegetative (green) can be grown may depend on the thickness of the vegetative
(green) roof planting media (including granular drainage
roof system. Planting media is typically formulated from a
mixture of component ingredients and is designed to satisfy media, in dual-media vegetative (green) roof systems), drain
specific performance requirements. In order to reduce dead layer type, and the intended use and function of the system.
load to roofs, many vegetative (green) roof systems utilize The system requirements vary with climate and level of
E2777 − 20
irrigation. In deep intensive systems, the upper layers of media and crushed shale may be introduced. Where a reliable source
may incorporate relatively more fine particles and organic of clean, crushed and classified demolition material is
matter.
available, crushed brick or terracotta can be also be used to
advantage.Extremecareshouldbetakenwhenconsideringany
7.3.1.2 Planting Media for Multi-Course Extensive Vegeta-
recycled building products for use as an aggregate or vegeta-
tive (Green) Roof Systems—Multi-course extensive vegetative
tive (green) roof media amendment should be tested to
(green) roof systems usually have a shallow media layer.
Extensive vegetative (green) roof systems can be designed to determine if it harbors any toxic materials. Carbonate materials
support succulents, grass, and a wide range of herbaceous should be avoided since these frequently result in carbonate
perennial and annual plants. Plant selections may be influenced
minerals precipitating on fabrics and in drainage facilities.
by the intended use and function of the vegetative (green) roof
7.3.2.2 Nutrient Retention Capacity/Cation Exchange Ca-
system, climate, degree of exposure of the roof surface to wind
pacity (CEC)—The mineral fraction of a planting mixture
and sun, and availability of irrigation. Many plants that are
serves additional functions for sustainability such as providing
adapted to extensive vegetative (green) roof systems have
cation exchange capacity (CEC) and pH buffering. Cation
shallow root systems or, in the case of sedums, are adversely
exchangecapacityofthemediaisameasureofthesoil’sability
affected by long periods of summer heat and nighttime
to attract and hold cations. Cations are positively charged ions
temperatures above 25 °C. Therefore, increasing the media
++ ++ +
like Ca ,Mg , and K which are also essential plant
layer may not improve plant performance but instead create
micro-nutrients. In most naturally occurring soils, this role is
adverse conditions that may prove to be detrimental to the
fulfilled by clay minerals. In vegetative (green) roof planting
plants in some instances.
media mixtures, clay and loam are avoided due to the threat of
7.3.1.3 Planting Media for Single-Course Extensive Vegeta-
fabriccloggingandreduceddrainagecapacity.Therefore,other
tive (Green) Roof Systems—Single-course extensive vegetative
mineral components may be selected that can contribute CEC
(green) roof systems are rarely thicker than 4 in. (10 cm). To
capacity to a vegetative (green) roof planting media mixture.
provide sufficient drainage, the media is generally coarser than
Laboratory testing of candidate materials and amendments is
that used in multi-coarse extensive vegetative (green) roof
necessary to determine the CEC potential. (To ensure ample
systems, and exhibits higher air-filled porosity and saturated
nutrient reserves in vegetative (green) roof media, an initial
hydraulic
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