ASTM E2400/E2400M-19

Standard Guide for Selection, Installation, and Maintenance of Plants for Vegetative (Green) Roof Systems

SIGNIFICANCE AND USE
5.1 This guide addresses performance characteristics for green roof systems with respect to the planting. A rooftop is an extreme environment with strong and variable wind patterns and little or no protection from the sun’s intense heat and ultraviolet radiation. Selection of plant material can be crucial for success of the green roof system.  
5.1.1 This guide provides general guidance only. It is important to consult with a professional horticulturist, green roof consultant, landscape architect, or work with similar professionals that are knowledgeable, experienced, and acquainted with green roof technology and plants.  
5.2 Determining these performance characteristics of green roof systems provides information to facilitate the assessment of engineering aspects of the facility. Such aspects may include structural design requirements, mechanical engineering and thermal design requirements, and fire and life safety requirements.  
5.3 Determining these performance characteristics of green roof systems provides information to facilitate assessment of the performance of one green roof system relative to another.
SCOPE
1.1 This guide covers the considerations for the selection, installation, and maintenance of plants for green roof systems.  
1.2 This guide is applicable to both extensive and intensive green roof systems.  
1.3 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.  
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and to determine the applicability of regulatory limitations prior to use.  
1.5 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.

General Information

• Status: Published
• Publication Date: 31-Dec-2018
• ICS: 65.020.20 - Plant growing
• Technical Committee: D08 - Roofing and Waterproofing
• Drafting Committee: D08.24 - Sustainability

Relations

• Replaces: ASTM E2400/E2400M-06(2015)e1 - Standard Guide for Selection, Installation, and Maintenance of Plants for Green Roof Systems
• Effective Date: 01-Jan-2019
• Refers: ASTM E2788/E2788M-24 - Standard 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
• Effective Date: 01-Jan-2024
• Refers: ASTM E2788/E2788M-18 - Standard 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
• Effective Date: 01-Mar-2018
• Refers: ASTM E2114-17 - Standard Terminology for Sustainability Relative to the Performance of Buildings
• Effective Date: 01-Feb-2017
• Refers: ASTM E631-15 - Standard Terminology of Building Constructions
• Effective Date: 01-Mar-2015
• Refers: ASTM E631-14 - Standard Terminology of Building Constructions
• Effective Date: 01-Nov-2014
• Refers: ASTM E2777-14 - Standard Guide for Vegetative (Green) Roof Systems
• Effective Date: 01-May-2014
• Refers: ASTM E2114-08 - Standard Terminology for Sustainability Relative to the Performance of Buildings
• Effective Date: 01-Nov-2008
• Refers: ASTM E2114-06a - Standard Terminology for Sustainability Relative to the Performance of Buildings
• Effective Date: 01-Dec-2006
• Refers: ASTM E631-06 - Standard Terminology of Building Constructions
• Effective Date: 01-Jun-2006
• Refers: ASTM E2114-06 - Standard Terminology for Sustainability Relative to the Performance of Buildings
• Effective Date: 15-Feb-2006
• Refers: ASTM E2114-05a - Standard Terminology for Sustainability Relative to the Performance of Buildings
• Effective Date: 01-Jun-2005
• Refers: ASTM E2114-05 - Standard Terminology for Sustainability Relative to the Performance of Buildings
• Effective Date: 01-Feb-2005
• Refers: ASTM E2114-04 - Standard Terminology for Sustainability Relative to the Performance of Buildings
• Effective Date: 01-Dec-2004
• Refers: ASTM E2114-00a - Standard Terminology for Sustainability Relative to the Performance of Buildings
• Effective Date: 10-Feb-2001

Overview

ASTM E2400/E2400M-19: Standard Guide for Selection, Installation, and Maintenance of Plants for Vegetative (Green) Roof Systems provides essential guidelines for planning, installing, and caring for green roofing plants. Issued by ASTM International, this standard applies to both extensive and intensive green roof systems and outlines key environmental, aesthetic, and performance factors for successful vegetative roofs. Green roofs provide benefits such as improved energy efficiency, urban heat island mitigation, enhanced stormwater management, and support for urban biodiversity. The guide is intended for architects, building engineers, landscape designers, and facility managers who aim to achieve sustainable and resilient green roof installations.

Key Topics

• Plant Selection Criteria
  The guide identifies significant factors influencing plant selection, including:

  • Design Intent: Accessibility, usage, thermal performance, wildlife habitat, and stormwater management objectives.
  • Aesthetics: Visual character, plant seasonality, and resilience to rooftop conditions.
  • Climate and Microclimate: Macro- and micro-climatic conditions such as solar exposure, wind, rainfall patterns, and temperature extremes.
  • Plant Characteristics: Establishment rate, longevity, pest and disease resistance, and non-invasiveness.
  • Media Composition and Depth: Media characteristics influence moisture retention, nutrient supply, and root protection.

• System Types

  • Extensive Green Roofs: Utilize hardy, low-maintenance plant species in shallow growing media, with lower installation costs and minimized structural demands.
  • Intensive Green Roofs: Feature deeper substrates supporting diverse plantings, including shrubs and trees, with increased structural and maintenance requirements.

• Installation Methods

  • Pre-cultivation: Plants or vegetative mats are grown off-site and installed for immediate coverage.
  • Direct Planting: Seeds, plugs, or root cuttings planted directly onto the roof substrate, often requiring additional establishment care.

• Maintenance Strategies

  • Irrigation: Guidance on passive (rainwater storage) and active irrigation systems tailored to plant requirements and climate conditions.
  • Regular Care: Weeding, occasional fertilization, inspection for plant health, and season-based adjustments.
  • Sustainability Considerations: Minimize use of chemicals that could compromise the roof membrane or environmental health.

Applications

ASTM E2400/E2400M-19 is widely used for green roof projects in both new construction and retrofit scenarios. Its practical recommendations help ensure plant selection is compatible with environmental stresses found on rooftops, promote long-term vegetative health, and support environmental goals such as sustainable building certification. Key applications include:

• Urban building retrofits looking to enhance energy efficiency and manage stormwater.
• Commercial developments targeting green building certifications (LEED, BREEAM, etc.).
• Municipal projects aiming to increase urban green space and reduce heat islands.
• Institutional and educational facilities wishing to integrate green infrastructure and biodiversity.

By following this standard, project teams can optimize plant survival, reduce maintenance needs, and maximize the functional benefits of vegetative roof systems.

Related Standards

Several ASTM standards complement E2400/E2400M-19 for green roof system success:

• ASTM E2777: Guide for Vegetative (Green) Roof Systems
• ASTM E2788/E2788M: Specification for Use of Expanded Shale, Clay, and Slate (ESCS) as Mineral Components in the Growing Media and Drainage Layer for Green Roofs
• ASTM E631: Terminology of Building Constructions
• ASTM E2114: Terminology for Sustainability Relative to the Performance of Buildings

These standards collectively support the design, installation, and ongoing management of efficient, resilient, and sustainable green roofing systems. For best results, consult a professional horticulturist or green roof consultant experienced with specific local conditions and building requirements.

Standards Content (Sample)

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: E2400/E2400M − 19
Standard Guide for
Selection, Installation, and Maintenance of Plants for
Vegetative (Green) Roof Systems
ThisstandardisissuedunderthefixeddesignationE2400/E2400M;thenumberimmediatelyfollowingthedesignationindicatestheyear
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 Growing Media and the Drainage Layer for Vegetative
(Green) Roof Systems
1.1 This guide covers the considerations for the selection,
installation, and maintenance of plants for green roof systems.
3. Terminology
1.2 This guide is applicable to both extensive and intensive
3.1 Definitions:
green roof systems.
3.1.1 For terms related to building construction, refer to
1.3 The values stated in either SI units or inch-pound units
Terminology E631.
are to be regarded separately as standard. The values stated in 3.1.2 For terms related to sustainability relative to the
each system may not be exact equivalents; therefore, each
performance of buildings, refer to Terminology E2114.
system shall be used independently of the other. Combining 3.1.3 For terms related to vegetative (green) roof systems,
values from the two systems may result in non-conformance
refer to Terminology E2777.
with the standard.
4. Summary of Guide
1.4 This standard does not purport to address all of the
4.1 This guide covers the selection criteria for plants to be
safety concerns, if any, associated with its use. It is the
used on green roofs. Primary considerations are as follows:
responsibility of the user of this standard to establish appro-
4.1.1 Design intent,
priate safety, health, and environmental practices and to
4.1.2 Aesthetics,
determine the applicability of regulatory limitations prior to
4.1.3 Climate; including both macroclimate and
use.
microclimate,
1.5 This international standard was developed in accor-
4.1.4 Plant characteristics, including the rate of
dance with internationally recognized principles on standard-
establishment, longevity, and disease and pest resistance, and
ization established in the Decision on Principles for the
4.1.5 Media composition and depth.
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
4.2 This guide covers the installation of plants for green
Barriers to Trade (TBT) Committee.
roofs. Installation methods include:
4.2.1 Pre-cultivation, and
2. Referenced Documents
4.2.2 Direct planting on roof (seeds, root cuttings, and
2.1 ASTM Standards:
plugs).
E631 Terminology of Building Constructions
4.3 Guidance is also provided for the maintenance of plants
E2114 Terminology for Sustainability Relative to the Perfor-
for green roofs.
mance of Buildings
E2777 Guide for Vegetative (Green) Roof Systems
5. Significance and Use
E2788/E2788M Specification for Use of Expanded Shale,
5.1 This guide addresses performance characteristics for
Clay and Slate (ESCS) as a Mineral Component in the
green roof systems with respect to the planting.Arooftop is an
extreme environment with strong and variable wind patterns
This guide is under the jurisdiction of ASTM Committee D08 on Roofing and
and little or no protection from the sun’s intense heat and
Waterproofingand is the direct responsibility of Subcommittee D08.24 on Sustain-
ultraviolet radiation. Selection of plant material can be crucial
ability.
for success of the green roof system.
Current edition approved Jan. 1, 2019. Published February 2019. Originally
5.1.1 This guide provides general guidance only. It is
approved in 2006. Last previous edition approved in 2015 as E2400/E2400M – 06
ɛ1
(2015) . DOI: 10.1520/E2400_E2400M-19.
important to consult with a professional horticulturist, green
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
roof consultant, landscape architect, or work with similar
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
professionals that are knowledgeable, experienced, and ac-
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. quainted with green roof technology and plants.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2400/E2400M − 19
5.2 Determining these performance characteristics of green inches in height, but this practice requires extensive labor.
roof systems provides information to facilitate the assessment Plants may look fantastic early in the year, but most cannot
of engineering aspects of the facility. Such aspects may include withstand summer heat and drought conditions when growing
structural design requirements, mechanical engineering and in shallow extensive roof media depths. In order to grow most
thermal design requirements, and fire and life safety require-
annuals, perennial flowering herbaceous plants, and grasses,
ments. either irrigation must be present or the media must be deeper.
If irrigation is not available, then succulent species such as
5.3 Determining these performance characteristics of green
sedum, sempervivum, and delosperma are considered good
roof systems provides information to facilitate assessment of
choices because of their ability to withstand extended drought
the performance of one green roof system relative to another.
and other adverse environmental conditions often present on a
rooftop. Unlike most perennials and grasses, succulents are not
6. Selection
considered fire hazards because of the large percentage of
6.1 In general, green roofs can be categorized into two
water that is stored in their leaves. The aesthetic value of the
types, intensive or extensive, depending on the plant material
roof will continually change throughout the growing season
and planned usage for the roof area.
and over time. Plant competition and succession will occur as
6.1.1 Intensive green roofs—Intensive green roofs utilize a
in any landscape, therefore intended patterns may lose sym-
wide variety of plant species that may include trees and shrubs
metry. Similarly, identical plant palettes will look and behave
and are generally limited to flat roofs. Use of large plants
differently depending on the local environmental conditions. In
requires deeper media layers, possibly 25 cm [10 in.] or more,
many cases extensive vegetative green roofs can be planned
which results in more weight and a need for an increased
and maintained to allow natural succession to take over. In
structural load capacity of the building. Intensive green roofs
some climates the conditions are right to allow for the natural
usually have higher requirements for water, labor and other
re-vegetation to become a natural meadow which requires
resources than extensive green roofs.
minimum maintenance such as removing invasive plants and
6.1.2 Extensive green roofs—Extensive green roofs use a
winter cleanup of dead vegetation.
narrow range of species limited to herbs, grasses, mosses, and
6.2.3 Climate—Climate has a major impact on plant selec-
drought tolerant succulents such as sedum, a succulent plant
tion. Typically, the microclimate of the roof will be different
known for its tolerance for extreme conditions. These types of
than the microclimate in the same location at grade. Microcli-
plants can potentially be sustained in a media layer as shallow
mates on a rooftop can dramatically affect plant health and
as 2.5 cm [1.0 in.] and, therefore, they can often be installed on
appearance and contribute to the failure of a green roof system.
buildings without the cost of major structural alterations.
Extensive green roofs generally require less maintenance and
6.2.3.1 In particular, average high and low temperatures,
are generally less expensive to install than intensive green
extreme hot and cold temperatures, wind, and the amount and
roofs.
distribution of rainfall throughout the year will determine what
species can survive in a specific area. Drought tolerance is
6.2 Criteria for Selecting Species:
important because high levels of solar radiation and low media
6.2.1 Design Intent—The design intent will impact plant
moisture are usually the norm, especially in shallow extensive
selection. Aspects of design intent that may influence plant
systems. Climatic conditions, especially the amount and dis-
selection include: accessibility and use of the roof, stormwater
tribution of rainfall and temperature extremes, will eliminate
management objectives, xeriscaping objectives, and thermal
the use of certain species or will dictate the need for irrigation.
insulation objectives. Considerations for wildlife, such as
establishing connections with a wildlife corridor or providing 6.2.3.2 Microclimate specific to the location must also be
habitat for wildlife of local ecosystems may also impact the considered. Surrounding structures may shade a portion of the
plant selection. Considerations for wildlife should be coordi- roof, thus altering the evapo-transpiration rate of the plants.
nated with a knowledgeable consultant and the regional Ex-
Drying winds will be stronger the greater the elevation of the
tension Service to verify anticipated wildlife in that climate at building and a roof built with different levels can cause
the rooftop elevation. changes in wind and sun patterns, leaving some areas hot and
6.2.1.1 The design intent and available installation and dry and other areas relatively cool and moist. Roof slope and
maintenance budgets are key factors is determining media orientation will influence the intensity of the sun, as south-
depths and plant selection. facing slopes will be drier and warmer than north-facing
6.2.2 Aesthetics—Aesthetics often drive green roof design slopes. Slope also affects water-holding capacity, as sloped
and plant selection. Combinations of evergreens and flowering roofs will drain faster due to the laws of gravity. Plants
plants with a long blooming season work well together. growing near the bottom of a slope will likely be greener
However, flowering perennial plants may recede into the because of higher media moisture content relative to the top.
ground during winter or long, hot, dry periods in the summer. This could be a factor in choosing plant species that will be
Iftheysurviveroofenvironmentalconditions,theywillusually successful. One must also consider the exhaust from air vents
regenerate themselves from the root system, but periods of for heating and air conditioning units as well as chemical
drought can leave a mass of browned-out, dead looking plants exhaust from industrial buildings. Reflective heat from adja-
that could be a fire hazard. Similarly, grasses are difficult to cent windows will be directed onto the green roof and will then
keep green throughout the summer. One can allow grasses to heat up that portion of the roof. This creates hot spots that will
grow until June and then cut them back to approximately three kill or damage certain plants. To avoid this scenario, shade
E2400/E2400M − 19
screens can be attached on the exterior of the windows tops of plants. In colder climates, it is especially important to
deflecting direct sunlight. identifythelowesttemperaturethattheareaexperiencesduring
winter. In southern climates, shallow media depth does not
6.2.4 Plant Characteristics—Other qualities usually consid-
provide root protection from radiant heat during warmer
ered desirable for green roof plants include rate of
seasons, deeper media allows the roots to move down to a
establishment, longevity, and disease and pest resistance.
cooler protected layer. In addition, a deeper medium is neces-
Sedums are CAM (crassulacean acid metabolism) plants which
sary for woody species, grasses, and many annual or perennial
exchange CO at night. If night time temperatures on the roof
flowering plants. In some cases, plant growth is stunted in a
are too high, above 22°C [70°F], the stomata may not open and
shallow medium due to restrictions in the root zone. However,
the
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
´1
Designation: E2400/E2400M − 06 (Reapproved 2015) E2400/E2400M − 19
Standard Guide for
Selection, Installation, and Maintenance of Plants for Green
Vegetative (Green) Roof Systems
This standard is issued under the fixed designation E2400/E2400M; 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.
ε NOTE—Units information was editorially corrected in January 2015.
1. Scope
1.1 This guide covers the considerations for the selection, installation, and maintenance of plants for green roof systems.
1.2 This guide is applicable to both extensive and intensive green roof systems.
1.3 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each
system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the
two systems may result in non-conformance with the standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and to determine the
applicability of regulatory limitations prior to use.
1.5 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.
2. Referenced Documents
2.1 ASTM Standards:
E631 Terminology of Building Constructions
E2114 Terminology for Sustainability Relative to the Performance of Buildings
E2777 Guide for Vegetative (Green) Roof Systems
E2788/E2788M 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
3. Terminology
3.1 Definitions:
3.1.1 For terms related to building construction, refer to Terminology E631.
3.1.2 For terms related to sustainability relative to the performance of buildings, refer to Terminology E2114.
3.1.3 For terms related to vegetative (green) roof systems, refer to Terminology E2777.
4. Summary of Guide
4.1 This guide covers the selection criteria for plants to be used on green roofs. Primary considerations are as follows:
4.1.1 Design intent,
4.1.2 Aesthetics,
4.1.3 Climate; including both macroclimate and microclimate,
4.1.4 Plant characteristics, including the rate of establishment, longevity, and disease and pest resistance, and
4.1.5 Media composition and depth.
4.2 This guide covers the installation of plants for green roofs. Installation methods include:
This guide is under the jurisdiction of ASTM Committee D08 on Roofing and Waterproofingand is the direct responsibility of Subcommittee D08.24 on Sustainability.
Current edition approved Jan. 1, 2015Jan. 1, 2019. Published February 2015February 2019. Originally approved in 2006. Last previous edition approved in 20062015 as
ɛ1
E2400E2400/E2400M – 06 (2015) -06. DOI: 10.1520/E2400_E2400M-06R15E01.10.1520/E2400_E2400M-19.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2400/E2400M − 19
4.2.1 Precultivation,Pre-cultivation, and
4.2.2 Direct planting on roof (seeds, root cuttings, and plugs).
4.3 Guidance is also provided for the maintenance of plants for green roofs.
5. Significance and Use
5.1 This guide addresses performance characteristics for green roof systems with respect to the planting. A rooftop is an extreme
environment with strong and variable wind patterns and little or no protection from the sun’s intense heat and ultraviolet radiation.
Selection of plant material can be crucial for success of the green roof system.
5.1.1 This guide provides general guidance only. It is important to consult with a professional horticulturist, green roof
consultant, landscape architect, or work with similar professionals that are knowledgeable, experienced, and acquainted with green
roof technology and plants.
5.2 Determining these performance characteristics of green roof systems provides information to facilitate the assessment of
engineering aspects of the facility. Such aspects may include structural design requirements, mechanical engineering and thermal
design requirements, and fire and life safety requirements.
5.3 Determining these performance characteristics of green roof systems provides information to facilitate assessment of the
performance of one green roof system relative to another.
6. Selection
6.1 In general, green roofs can be categorized into two types, intensive or extensive, depending on the plant material and
planned usage for the roof area.
6.1.1 Intensive green roofs—Intensive green roofs utilize a wide variety of plant species that may include trees and shrubs and
are generally limited to flat roofs. Use of large plants requires deeper media layers, possibly 25 cm [10 in.] or more, which results
in more weight and a need for an increased structural load capacity of the building. Intensive green roofs usually have higher
requirements for water, labor and other resources than extensive green roofs.
6.1.2 Extensive green roofs—Extensive green roofs use a narrow range of species limited to herbs, grasses, mosses, and drought
tolerant succulents such as sedum, a succulent plant known for its tolerance for extreme conditions. These types of plants can
potentially be sustained in a media layer as shallow as 2.5 cm [1.0 in.] and, therefore, they can often be installed on buildings
without the cost of major structural alterations. Extensive green roofs generally require less maintenance and are generally less
expensive to install than intensive green roofs.
6.2 Criteria for Selecting Species:
6.2.1 Design Intent—The design intent will impact plant selection. Aspects of design intent that may influence plant selection
include: accessibility and use of the roof, stormwater management objectives, xeriscaping objectives, and thermal insulation
objectives. Considerations for wildlife, such as establishing connections with a wildlife corridor or providing habitat for wildlife
of local ecosystems may also impact the plant selection. Considerations for wildlife should be coordinated with a knowledgeable
consultant and the regional Extension Service to verify anticipated wildlife in that climate at the rooftop elevation.
6.2.1.1 The design intent and available installation and maintenance budgets are key factors is determining media depths and
plant selection.
6.2.2 Aesthetics—Aesthetics often drive green roof design and plant selection. Combinations of evergreens and flowering plants
with a long blooming season work well together. However, flowering perennial plants may recede into the ground during winter
or long, hot, dry periods in the summer. If they survive roof environmental conditions, they will usually regenerate themselves from
the root system, but periods of drought can leave a mass of browned-out, dead looking plants that could be a fire hazard. Similarly,
grasses are difficult to keep green throughout the summer. One can allow grasses to grow until June and then cut them back to
approximately three inches in height, but this practice requires extensive labor. Plants may look fantastic early in the year, but most
cannot withstand summer heat and drought conditions when growing in shallow extensive roof media depths. In order to grow most
annuals, perennial flowering herbaceous plants, and grasses, either irrigation must be present or the media must be deeper. If
irrigation is not available, then succulent species such as sedum,sempervivum, and delosperma are considered good choices
because of their ability to withstand extended drought and other adverse environmental conditions often present on a rooftop.
Unlike most perennials and grasses, succulents are not considered fire hazards because of the large percentage of water that is
stored in their leaves. The aesthetic value of the roof will continually change throughout the growing season and over time. Plant
competition and succession will occur as in any landscape. landscape, therefore intended patterns may lose symmetry. Similarly,
identical plant palettes will look and behave differently depending on the local environmental conditions. In many cases extensive
vegetative green roofs can be planned and maintained to allow natural succession to take over. In some climates the conditions
are right to allow for the natural re-vegetation to become a natural meadow which requires minimum maintenance such as
removing invasive plants and winter cleanup of dead vegetation.
6.2.3 Climate—Climate has a major impact on plant selection. Typically, the microclimate of the roof will be different than the
microclimate in the same location at grade. Microclimates on a rooftop can dramatically affect plant health and appearance and
contribute to the failure of a green roof system.
E2400/E2400M − 19
6.2.3.1 In particular, average high and low temperatures, extreme hot and cold temperatures, wind, and the amount and
distribution of rainfall throughout the year will determine what species can survive in a specific area. Drought tolerance is
important because high levels of solar radiation and low media moisture are usually the norm, especially in shallow extensive
systems. Climatic conditions, especially the amount and distribution of rainfall and temperature extremes, will eliminate the use
of certain species or will dictate the need for irrigation.
6.2.3.2 Microclimate specific to the location must also be considered. Surrounding structures may shade a portion of the roof,
thus altering the evapo-transpiration rate of the plants. Drying winds will be stronger the greater the elevation of the building and
a roof built with different levels can cause changes in wind and sun patterns, leaving some areas hot and dry and other areas
relatively cool and moist. Roof slope and orientation will influence the intensity of the sun, as south-facing slopes will be drier
and warmer than north-facing slopes. Slope also affects water-holding capacity, as sloped roofs will drain faster due to the laws
of gravity. Plants growing near the bottom of a slope will likely be greener because of higher media moisture content relative to
the top. This could be a factor in choosing plant species that will be successful. One must also consider the exhaust from air vents
for heating and air conditioning units as well as chemical exhaust from industrial buildings. Reflective heat from adjacent windows
will be directed onto the green roof and will then heat up that portion of the roof. This creates hot spots that will kill or damage
certain plants. To avoid this scenario, shade screens can be attached on the exterior of the windows deflecting direct sunlight.
6.2.4 Plant Characteristics—Other qualities usually considered desirable for green roof plants include rate of establishment,
longevity, and disease and pest resistance. Sedums are CAM (crassulacean acid metabolism) plants which exchange CO at night.
If night time temperatures on the roof are too high, above 22°C [70°F], the stomata may not open and the plants will go dormant.
Broadleaf sedums such as Sedum kamstschaticum perform better in southern climates by shading the media and reducing the
radiant heat. Low growing plants that spread rapidly to cover the media reduce potential erosion problems and inhibit weeds.
Although, rapid coverage is important, the lifespan of these plants should be considered, as many rapidly spreading plants may
be short-lived. The ability of the plant species to be self-sustaining reduces the need for future replanting and maintenance. Species
that are long-lived, that reseed themselves, or spre
...