Green wall systems: A review of their characteristics

Abstract

a b s t r a c t Current systems for greening the buildings envelope are not just surfaces covered with vegetation. Greening systems, as green roofs and green walls, are frequently used as an aesthetical feature in buildings. However, the current technology involved in these systems can maximize the functional benefits of plants to buildings performance and make part of a sustainable strategy of urban rehabilitation and buildings retrofitting. During the last decades several researches were conducted proving that green walls can contribute to enhance and restore the urban environment and improve buildings performance. The aim of this paper is to review all types of green wall systems in order to identify and systematize their main characteristics and technologies involved. So, it is important to understand the main differences between systems in terms of composition and construction methods. Most recent developments in green walls are mainly focused in systems design in order to achieve more efficient technical solutions and a better performance in all building phases. Yet, green wall systems must evolve to become more sustainable solutions. In fact, continuing to evaluate the contribution of recent green wall systems to improve buildings performance and comparing the environmental impact of these systems with other construction solutions can lead to an increase of their application in buildings and therefore result in a reduction on these systems cost. The decision of which green wall system is more appropriate to a certain project must depend not only on the construction and climatic restrictions but also on the environmental impact of its components and associated costs during its entire lifecycle.

Full text

Green wall systems: A review of their characteristics
Maria Manso
n
, João Castro-Gomes
C-MADE, Centre of Materials and Building Technologies, Department of Civil Engineering and Architecture, University of Beira Interior,
Calçada Fonte do Lameiro Edifício II das Engenharias, 6201-001 Covilhã, Portugal
article info
Article history:
Received 8 January 2014
Received in revised form
27 May 2014
Accepted 30 July 2014
Keywords:
Green wall systems
Green facades
Living walls
Classification
Composition
abstract
Current systems for greening the buildings envelope are not just surfaces covered with vegetation. Greening
systems, as green roofs and green walls, are frequently used as an aesthetical feature in buildings. However,
the current technology involved in these systems can maximize the functional benefits of plants to buildings
performance and make part of a sustainable strategy of urban rehabilitation and buildings retrofitting.
During the last decades several researches were conducted proving that green walls can contribute to
enhance and restore the urban environment and improve buildings performance.
The aim of this paper is to review all types of green wall systems in order to identify and systematize
their main characteristics and technologies involved. So, it is important to understand the main differences
between systems in terms of composition and construction methods.
Most recent developments in green walls are mainly focused in systems design in order to achieve more
efficient technical solutions and a better performance in all building phases. Yet, green wall systems must
evolve to become more sustainable solutions. In fact, continuing to evaluate the contribution of recent green
wall systems to improve buildings performance and comparing the environmental impact of these systems
with other construction solutions can lead to an increase of their application in buildings and therefore result
in a reduction on these systems cost.
The decision of which green wall system is more appropriate to a certain project must depend not only
on the construction and climatic restrictions but also on the environmental impact of its components and
associated costs during its entire lifecycle.
&2014 Elsevier Ltd. All rights reserved.
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 863
2. Classification and definition...........................................................................................864
2.1. Green facades. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 864
2.2. Living walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 865
3. Systems requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 866
3.1. Supporting elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 866
3.2. Growing media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 867
3.3. Vegetation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 867
3.4. Drainage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 868
3.5. Irrigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 868
3.6. Installation and maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 868
3.7. Environmental performance and costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 869
4. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 870
Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 870
Appendix A. Supporting information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 870
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 870
Contents lists available at ScienceDirect
journal homepage: www.elsevier.com/locate/rser
Renewable and Sustainable Energy Reviews
http://dx.doi.org/10.1016/j.rser.2014.07.203
1364-0321/&2014 Elsevier Ltd. All rights reserved.
n
Corresponding author.
E-mail addresses: mcfmm@ubi.pt (M. Manso), castro-gomes@ubi.pt (J. Castro-Gomes).
Renewable and Sustainable Energy Reviews 41 (2015) 863–871

1. Introduction
Current systems for greening the buildings envelope are not
just surfaces covered with vegetation. There are several greening
systems in the market, like green roofs and green walls, which
technology involved is being developed to increase their perfor-
mance and longevity.
Greening systems, as green roofs and green walls, are fre-
quently used as an aesthetical feature in buildings. However, the
current technology involved in these systems can maximize the
functional benefits of plants to buildings performance [1]. Green-
ing systems can also make part of a sustainable strategy [2–4] of
urban rehabilitation and building retrofitting [5–7].
At a city scale, green roofs and green walls contribute to the
insertion of vegetation in the urban context without occupying
any space at street level [8]. In fact, covering buildings with
vegetation, when applied in a significant urban scale, can improve
the urban environment by contributing to urban biodiversity [1,9],
stormwater management [10], air quality [11–13], temperature
reduction [14] and mitigation of the heat island effect [15,16].
At the same time, the application of greening systems can have,
besides the environmental aspects, social and economic benefits.
These systems encourage the fruition of urban areas [17],havea
therapeutic effect by inducing a psychological wellbeing through
the presence of vegetation, improve cities image [7], increase
property value [18] and function as a complementary thermal [19]
and acoustic protection [20,21].
Green walls have a greater potential than green roofs consider-
ing that in urban centers the extent of facade greening can be
double the ground footprint of buildings [22].
At a building scale, green wall systems can be used as a passive
design solution [23] contributing to buildings sustainability per-
formance [24]. Vegetation has the potential to improve the
microclimate both in winter [25], functioning as a complementary
insulation layer, and in summer [26], providing shade [27–29] and
an evaporative cooling effect [30]. Vegetation absorbs large
amounts of solar radiation [31] while the effect of evapotranspira-
tion of plants can further reduce the impact of solar radiation,
showing increased humidity levels and surface temperatures
lower than hard surfaces [32,33]. Recent studies show that green
wall systems have the ability to control heat gains and losses,
contributing to improve indoor thermal comfort and reduce
energy demands for heating or cooling [15,34–36].
Green wall is the common term to refer to all forms of
vegetated wall surfaces. Traditional green wall methods are
historically known, since the Hanging Gardens of Babylon and
the Roman and Greek Empires. In Mediterranean climates, vines
were commonly used to cover pergolas, shading the building
envelope, or on building walls, cooling the envelope during
summer [37]. Since the seventeenth and eighteenth centuries,
mostly in UK and Central Europe, the use of climbing plants to
cover building walls proliferated [38]. In the 19th century woody
climbers were commonly used as ornamental elements of build-
ings envelope in European and North American cities [39].
First investigations on green facades were based on botanical
aspects [22]. However, since the 1980s a new idea occurred of green
facades as contributors to cities ecological enhancement. The garden
city movement from the end of the 19th century marked the
integration of greening in urban planning. The German Jugendstil
movement (Art Nouveau) from the early 20th century encouraged the
integration of the house with the garden. During this period emerged
some incentive programs for the installation of green facades. In fact,
Berlin is an important example, from 1983 to 1997, where around
245.584 square meters of green facades were installed [22].
This paper aims to review the main green wall systems
available, systematizing their main characteristics and technology
involved. A search of green walls, available internationally on the
market or in invention databases (e.g., Esp@cenet, Free Patents
Online, Fresh Patents, Google Patents, Lusopat, Wipo –Patent-
scope), allowed the identification and characterization of most of
the existing green wall systems. It must be noticed that this is a
field in constant actualization. However, the analyzed solutions
constitute a representative universe to identify the main features
of green walls in terms of configuration, composition and
materials used.
This paper is divided in two main sections. First, a classification
of green wall systems, including a definition for different systems
according to their characteristics is proposed. Second, the main
requirements of different green wall systems in terms of composi-
tion, processes of installation and maintenance and their environ-
mental impact and cost are systematized.
In order to compare the several green wall systems and their
features, an analysis of their composition is made according to the
following items: supporting elements, growing media, vegetation,
drainage and irrigation. Additionally, given the importance of
these subjects, two subsections were added to focus, first on the
different phases of the systems lifecycle, namely on the differences
on their installation and maintenance, and second on the environ-
mental performance and cost of green wall systems.
2. Classification and definition
Considering the recent developments in green walls technology
it is important to identify and classify all existing green wall
systems, according to their construction techniques and main
characteristics.
Authors use several nomenclatures when referring to all types
of green wall systems. Some use the term “vertical garden”[40,41]
others call them “vertical greening systems”[42],“green vertical
systems”[23] or “vertical greenery systems (VGSs)”[43]. When
referring to direct or indirect green facades, Ottelé et al. and Perini
et al. [44,45] used the terms direct greening systems and indirect
greening systems, respectively.
Another concept called “Biowalls”was mentioned by Francis
et al. regarding the application of green walls in indoor spaces in
order to enhance the environment [9].
This concept includes the technology involved in living walls;
therefore it can be inserted in this category.
In fact, the concept of green walls refers to all systems which
enable greening a vertical surface (e.g., facades, walls, blind walls,
partition walls, etc.) with a selection of plant species, including all
the solutions with the purpose of growing plants on, up or within
the wall of a building [38]. In this paper a classification of green
walls according to the different existing systems and their con-
struction characteristics is proposed (see Fig. 1).
Green walls can be subdivided in two main systems: green
facades and living walls [22,39]. There is an evident distinction
between green facades, where usually climbing plants grow along
the wall covering it, and the most recent concepts of living walls,
which include materials and technology to support a wider variety
of plants, creating a uniform growth along the surface.
2.1. Green facades
Green facades are based on the application of climbing or
hanging plants along the wall. Plants can grow upwards the
vertical surface, like traditional examples, or grow downward the
vertical surface, in case they are hanged at a certain height [39].
Green facades can be classified as direct or indirect. Direct
green facades are the ones in which plants are attached directly to
M. Manso, J. Castro-Gomes / Renewable and Sustainable Energy Reviews 41 (2015) 863–871864

the wall. Indirect green facades include a supporting structure for
vegetation.
Traditional green facades are considered a direct greening
system, consisting on using self-clinging climbers, rooted directly
in the ground (see Fig. 2).
New solutions of green facades are usually indirect greening
systems, which include a vertical support structure for climbing
plants development. In these examples plants can be rooted
directly in the ground or in planters, and be guided to develop
along the support structure.
Indirect greening systems include continuous and modular
solutions. Continuous guides are based on a single support
structure that directs the development of plants along the entire
surface (see Fig. 3). Green facades with modular trellises are
similar solutions, but result from the installation of several
modular elements along the surface. The main differences are
that modular trellises have vessels for plants rooting and an
individual support structure for guiding plants development [46].
2.2. Living walls
Living walls are a quite recent area of innovation in the field of
wall cladding. They emerged to allow the integration of green
walls in high buildings. Living walls allow a rapid coverage of large
surfaces and a more uniform growth along the vertical surface,
reaching higher areas and adapting to all kinds of buildings. They
also allow the integration of a wider variety of plant species.
Living wall systems (LWS) can be classified as continuous or
modular, according to their application method. Continuous LWS
are based on the application of lightweight and permeable screens
in which plants are inserted individually [47,48]. Modular LWS are
elements with a specific dimension, which include the growing
Fig. 2. Direct green facade, private house, Golegã, Portugal. Fig. 3. Indirect green facade.
Green walls
Green facades
Direct Traditional green facades
Indirect
Continuous guides
Modular trellis
Living walls (LWS)
Continuous Lightweight screens
Modular
Trays
Vessels
Planter tiles
Flexible bags
Fig. 1. Classification of green walls, according to their construction characteristics.
Fig. 4. Continuous living wall system, Caixa Forum, Madrid, June 2013.
M. Manso, J. Castro-Gomes / Renewable and Sustainable Energy Reviews 41 (2015) 863–871 865

media where plants can grow. Each element is supported by a
complementary structure or fixed directly on the vertical surface.
Continuous LWS are also known as Vertical Gardens, a name
given by the French botanist Patrick Blanc who reported his first
“Vertical Garden”, also designated as “Mur Vegetal”in 1994.
Patrick Blanc spread the application of this type of LWS all around
the world. His work is included in several buildings of the most
famous architects (see Fig. 4).
In the category of living wall systems, the alternative to vertical
gardens is the application of modular living wall systems (see
Fig. 5), which is relatively new [39]. Modular LWS have differences
in their composition, weight and assembly. They can be in the
form of trays, vessels, planter tiles or flexible bags.
Trays are usually rigid containers, attachable to each other, that
can hold the plants and substrate weight.
Vessels are an adaptation of the most common support for
plants with the difference that they can be fastened to a vertical
structure or be attached vertically to each other.
Planter tiles highlight the modular elements shape as elements
of design for building's exterior or interior cladding. More than the
creation of vegetation layer, they function as a modular cladding
with insertions for plants.
Flexible bags include a growing media and lightweight materi-
als that allow the application of vegetation in surfaces with
different forms, as curved or sloped surfaces.
3. Systems requirements
Most recent developments in green walls are mainly focused
in systems design and their elements (supporting elements, growing
media, vegetation, irrigation and drainage) in order to achieve more
efficient technical solutions and a better performance in all building
phases (installation, maintenance and replacement).
The adaptability to more building types (e.g., commercial
spaces, high rise buildings), construction methods (new or existing
building walls) and types of surfaces (e.g., sloping surfaces, indoor
partition walls and free-standing structures) [49,50] is also the
concern in the evolution of green wall systems.
3.1. Supporting elements
Traditional or direct green facades usually have no support
structure. They rely on the capacity of climbing plants to attach
themselves to the vertical surface. However, when the vegetation
fulfils full coverage can become too heavy and the risk of falling is
increased.
Indirect green facades function as “double-skin facades”, creat-
ing an air gap between the building surface and vegetation.
The application of a support structure avoids vegetation to fall.
These systems, either modular or continuous, anchor and hold the
vegetation weight, contributing to increase the system resistance
to environmental actions (e.g., wind, rain, snow). Most support
structures for indirect green facades include continuous or mod-
ular guides, as cables, wires or trellis made of galvanized or
stainless steel [51,52]. Steel structures and tensile cables (see
Fig. 6) can be used to hold climbing plants with denser foliage
and to support their weight. Grids and wire-nets have smaller
intervals and can be used for slow growing plants support [53].
Some indirect green facades systems, mostly modular trellises,
include pots filled with substrate and individual support struc-
tures, allowing the suspension of the elements along the wall at
various heights. New forms of modular trellises include a curved
grid to give the facade rhythm and three-dimensionality to the
wall [51,52].
Living walls usually include a frame to hold the elements and a
support for plants.
Continuous LWS are based on the installation of a frame fixed
to the wall, forming a void space between the system and the
surface. This frame holds the base panel and protects the wall from
humidity. The base panel supports the next layers. It is covered
with layers of permeable, flexible and root proof screens, stapled
to the base. The external layer of screen is then cut to form pockets
[47,48] for the introduction of plants individually (see Fig. 7).
Modular LWS can take several forms (e.g., trays, vessels, planter
tiles or flexible bags) requiring a different structure.
Modular trays are usually composed of several interlocked
parts, made of lightweight materials as plastic (e.g., polypropylene
or polyethylene) or metal sheets (e.g., aluminum, galvanized steel
or stainless steel) [54–59].To ensure the system continuity, each
module normally includes an interlocking system on the sides to
connect to each other. These modular elements may also contain a
front cover forming a grid to prevent plants to fall (see Fig. 8).
Trays and vessels are usually fixed to a vertical and/or hor-
izontal frame attached to the surface. The back surface can include
hooks or mounting brackets [56,58] for their suspension in the
frame profiles connected to the vertical surface.
Modular vessels allow the installation of several plants in each
element along the same row. They are commonly made with
polymeric materials and due to their form have a significant visual
impact on the building surface.
Fig. 6. Continuous green facade.
Fig. 5. Modular living wall system, Natura Towers, Lisbon, August 2012.
M. Manso, J. Castro-Gomes / Renewable and Sustainable Energy Reviews 41 (2015) 863–871866

Planter tiles are connected to each other by juxtaposition. They
often include a flat back fixed to the building surface and an area
in which the plants are inserted individually. These solutions can
be built in lightweight or porous materials like plastic or ceramics
[60]. Depending on the system, tiles can be glued to the vertical
surface [61] or be fixed with mechanical fastening [60].
Modular LWS can also take the form of elongate bags, filled
with growing media, made of flexible polymeric materials which
are cut to insert each plant [62].
3.2. Growing media
In the context of green facades only modular systems require
the selection of a growing media, which must be lightweight,
considering that each element will be suspended, and adapted to
the selected plant species and environmental conditions.
In the field of living walls, continuous LWS also do not have
substrate. As mentioned before, these systems use lightweight
absorbent screens where plants are inserted in pockets. Contin-
uous LWS are commonly based on a hydroponic method, requiring
a permanent supply of water and nutrients due to the lack of
substrate. Hydroponic systems allow the growth of plants without
soil, using screens constantly moist by the irrigation system. The
lack of soil is compensated by providing the necessary nutrients
for plants development through irrigation water.
Modular LWS are commonly filled with a growing media where
roots can proliferate, made of organic and inorganic compounds
[49,58,59] or include a layer of inorganic substrate, usually foam,
to reduce its weight. Most modular LWS include a growing media
based on a mixture of light substrate with a granular material,
expanded or porous (e.g., mineral granules with medium to fine
particles, coconut fibbers or recycled fabric) in order to obtain a
good water retention capacity [56,63]. The substrate may be
improved with nutrients for plants growth (e.g., mixture of organic
and inorganic fertilizers, metal chelates, minerals, nutrients and
hormones for plants or other additives) [58]. Some modular LWS
indicate the insertion of growing media into geotextile bags to
prevent its detachment. These bags can occupy the entire module
and allow the insertion of several plants [56], or cover the growing
media of each plant individually [54,57]. Alternatively, each plant
can include an individual front cover to avoid the growing media
to fall [58].
3.3. Vegetation
The appropriate vegetation depends on climatic conditions, the
building characteristics and the surrounding conditions, in which
the green wall is inserted. The analyzed systems show some
concerns with vegetation longevity.
Climbing plants are considered a cheap solution of vertical
greening. These plant species can contain two main types of
foliage, evergreen or deciduous. Evergreen plants maintain their
leaves all year and deciduous plants lose their leaves during the
fall, having a strong visual change along the year.
Climbing plants can be self-supporting, attaching themselves to
the vertical surface (e.g., root climbers and adhesive-suckers) or be
supported by a structure [52] were they can hold (e.g., twining
vines, leaf–stem climbers, leaf climbers and scrambling plants).
They were traditionally used in Germany and France to cover the
exterior walls of small buildings. In warm-summer climates vines
were commonly installed in pergolas to shade buildings envelope
[39]. It is also important to consider that climbing plants have
growing limitations. Some species achieve 5 or 6 m, others 10 m
and some 25 m high [39] and take about 3–5 years to achieve full
coverage [53].
A study performed in the Mediterranean Continental climate
compared the development of several climbing plants, perennials
(Hereda helix, Lonicera japonica) and deciduous (Parthenocissus
quinquefolia, Clematis sp), according to the achieved foliage density
after one year of development. It revealed that Parthenocissus
quinquefolia, also known as Virginia creeper, provided greater
density of foliage, but none of the selected species could cover
the entire surface after one year. Some species also reveal
difficulties to adapt to the climatic conditions, with high tempera-
ture variations along the year and low rainfall, as Clematis which
was affected by summer conditions [30].
Living wall systems allow the development of new aesthetical
concepts of green walls, based on the creation of artistic solutions
with plant species, exploring the use of patterns, variations in
color, texture, foliage forms and density, vitality and growth. These
solutions brought a wider variety of plant species to green walls,
allowing the integration of shrubs, grasses and several perennials
as long as their watering and nutrient needs are taken into
account.
Hydroponic systems make possible the growth of a wider
variety of plants, in different states of development: grown plants,
cuttings or seeds [64]. In these cases vegetation is selected
according to the desired aesthetic effect [56,65], requiring the
appropriate irrigation and nutrients for an adequate plant devel-
opment. Therefore, it is important to analyze plants develop-
ment, color, blooming, foliage and the global plant composition,
Fig. 7. Continuous living wall system.
Fig. 8. Modular living wall system.
M. Manso, J. Castro-Gomes / Renewable and Sustainable Energy Reviews 41 (2015) 863–871 867

according to the artistic intentions to a certain building (e.g.,
building framing in the urban context, advertisement of a parti-
cular company, or marking distinction of an certain building or
interior space).
However, in order to fulfill sustainability goals, vegetation must
have low irrigation needs (e.g., use of native plants), be adapted to
local conditions of exposure (e.g., sun, semi-shade or shade) and
weather conditions (e.g., wind, rainfall, heat, drought and frost).
Recent examples of modular LWS include the option of using
succulent carpets in green walls instead of perennials and shrubs.
The use of drought tolerant plant species as succulents [1] reduces
the needs of irrigation. These plant species have also low main-
tenance and contribute to the minimization of the system weight.
However, succulent carpets acquire the appearance of a flat
vegetated surface, which can be interesting in small walls. In
larger surfaces the use of perennials and shrubs allows the
creation of more ornamented landscapes due to the variety of
colors and textures that these plants can include. A Japanese
system [62] also exemplifies the application of certain shrubs
which can be used in inclined surfaces (e.g., Juniperus chinensis,
Juniperus conferta,Euonymus Fortunei,Cotoneaster,Cotoneaster
Horizontal, Vitex rotundifolia).
Green walls have a particular potential for urban agriculture,
particularly in cities where there is lack of land for cultivation,
reducing the environmental impact related to food production and
distribution [53]. New concepts of green walls consider the
integration of vegetables and aromatic herbs in green facades,
continuous LWS [48] or modular LWS (Fig. 9), as planters [60] or
vessels [61], increasing the functional potential of the system itself
to building users.
3.4. Drainage
Excess fluid drainage in green walls takes place by gravity.
Continuous and modular LWS use geotextiles that encourage
drainage along the permeable membrane while preventing roots
proliferation.
Modular trays take advantage of the overlap of modules and
materials to improve drainage and water excess reuse to the
modules below. For a better drainage the bottom of a modular
systems can be concave, inclined, perforated or be made in a
porous or absorbent material [55]. Other examples as vessels
mention the use of a filter material applied at the bottom of the
module [61] (e.g., inoculated sand or other mean to purify rain-
water, remove toxins and heavy metals) or a granular inert filler
[65] (e.g., expanded clay, expanded slate, gravel) which promotes
the drainage and development of roots. Some examples of mod-
ular systems also mention the insertion of grooves or holes on the
sides and back face of modules, for a better aeration and removal
of excess moisture contained in the substrate [56,59].
3.5. Irrigation
The irrigation needs depend on the type of system, plants used
and climatic conditions.
Modular green facades and LWS require an irrigation system in
order to provide the necessary water to plants development. The
irrigation water can be enriched with nutrients, fertilizers, miner-
als, phosphates, amino acids or hydroponic materials to improve
the vegetation development and vivacity.
The water supply of LWS is made through the installation of a
continuous irrigation tube located at the top. Continuous LWS
have an irrigation system installed at the structure top connected
to the central irrigation system. In the case of continuous LWS the
permeable screen allows the uniform distribution of water and
nutrients along the surface.
Some modular LWS in the form of trays include a recess in the
top face of the module to insert the irrigation tube. The trays
include several holes in the recess for watering the growing media
by gravity [54,55,57,58]. Drainage holes located in trays bottom are
used to allow excess water to irrigate the modules underneath.
The irrigation tubes and connectors can be produced in several
materials (e.g., rubber, plastics, piping thermoplastic, silicone and
irrigation hose) containing different outputs (e.g., drip, sprinkler,
holes, pipe) with distribution and intensity adapted to the plants
irrigation needs. The irrigation system can also include a filtration
system to prevent clogging.
Some LWS also mention strategies for minimizing the con-
sumption of treated water. There are strategies like rainwater
recovery [56] from the building roofs, reuse of the fluid collected
in the drainage system [67] and monitoring water supply needs
[55], through the installation of sensors [47,48] that control the
collecting water tank level, the irrigation time and weather
conditions (e.g., quantity of rainfall, humidity, temperature, atmo-
spheric pressure).
Other LWS, either modular [60,68] or continuous [47,48], also
refer the installation of a gutter in the system base, recovering
excess water storing it and reintroducing it into the irrigation
system.
Another strategy consists in the application of sensors in the
growing media for nutrients needs quantification. This can be
important to minimize nutrients consumption and match the
plants needs.
3.6. Installation and maintenance
Green facades, including climbing species, are more cost-
effective during the installation process but have limitations in
plants diversity. When there is the necessity of plants replace-
ment, these systems show difficulties in ensuring vegetation
continuity. During plants growth, some climbing plants also
require guidance to ensure that they cover the entire surface. It
is also important to refer that some climbing plants can damage
buildings surface, destroying it with their roots and entering in
voids or cracks.
Modular trellises have advantages when compared to contin-
uous guides on the installation and maintenance processes. The
installation of plants at several heights decreases significantly the
impact of the disperse growth of climbing plants along the surface
and enables the substitution of unsuccessful plants.
A crescent number of modular LWS emerge in the market to
minimize installation, maintenance and replacement problems.
Fig. 9. Modular living wall with edible plants [66].
M. Manso, J. Castro-Gomes / Renewable and Sustainable Energy Reviews 41 (2015) 863–871868

Some modular systems enable to disassemble each module
individually [59] or include a removable front cover [57] for wall
maintenance or vegetation replacement. Some modular elements
can also be nested into each other in order to simplify the
transportation and application processes.
When comparing continuous LWS to modular LWS, continuous
LWS enable the creation of vegetated surfaces with a wider variety
of plant species, and can be lighter, has a density of around thirty
plants per square meter and less than 30 kg/m
2
[64]. However,
continuous LWS are commonly hydroponic systems, requiring a
permanent supply of water and nutrients, which constitute a
sustainability disadvantage and result in higher maintenance costs
due to higher irrigation needs.
In fact each green wall system has its own characteristics, with
advantages and disadvantages depending on their aesthetic poten-
tial, cost and maintenance needs (Table 1). The selection of the
most adequate system is directly related to the building character-
istics (e.g., orientation, accessibility, height) and climatic condi-
tions (e.g., sun, shade and wind exposure, rainfall). This is why it is
important to understand their differences in composition and
their main characteristics (Table 2).
3.7. Environmental performance and costs
To better understand if green wall systems may be considered
sustainable solutions, several studies were conducted by researchers
to compare the environmental performance of different green walls
systems during their entire lifecycle.
Direct green facades are a more sustainable [69] and economic
solution [45]. These systems have a small environmental burden
considering that they have no materials involved and have low
maintenance needs.
When analyzing the life cycle of some LWS their sustainability
may be questioned. Differences in the type of materials used, their
durability, recycling potential, vegetation durability and water
consumption can have a significant impact on the total environ-
mental burden [44,70]. As shown by Ottelé et al. the integration of
stainless steel as supporting system can have an impact 10 times
higher than using other recycled materials (e.g., HDPE, hard wood
with FSC certificate or coated steel) [44]. Another important
matter is materials durability. Several materials as PVC and others
have a limited durability requiring its replacement more than once
during buildings life expectancy.
Nevertheless, green wall systems frequently use materials with
high environmental impact. Recent studies proof that some
systems can have a reduced environmental burden by contributing
to the thermal resistance of the wall, leading to a reduction on
energy demand for heating and cooling [44].
The cost of green wall systems can also be a variable with
significant impact on the selection process. LWS are more expen-
sive when compared to direct and indirect green facades. Direct
and indirect green facades can cost less than 75 €/m
2
[45].
Table 1
Comparison of green wall systems advantages and disadvantages.
System Category Sub-category Advantages Disadvantages
Green facades Direct greening Traditional green
facades
No materials involved (support, growing media,
irrigation) [71]
Limited plant selection/climate adaptability
Low environmental burden [44] Spontaneous vegetation development [45]
Low cost [45] Slow surface coverage [53]
Scattered growth along the surface [23]
Surface deterioration [23,39]/plants detachment
Maintenance problems [33,45]
Indirect greening Continuous guides Vegetation development guidance [53] Limited plant selection/climate adaptability
[30,71]
Low water consumption [71] Slow surface coverage [53]
Scattered growth along the surface [23,26]
High environmental burden of some materials
[44,71]
Modular trellis Lightweight support [23] Limited plant selection/climate adaptability [46]
Vegetation development guidance [51] High environmental burden of some materials
Controlled irrigation/drainage [51] High installation cost [45]
Easiness to assemble and disassemble for
maintenance [30]
Plants replacement
Living walls Continuous systems Felt pockets vertical
gardens
Uniform growth [71] Complex implementation [23]
Flexible and lightweight [47,48] High water and nutrients consumption [71]
Increased variety of plants/aesthetic potential
[45,64,71]
Frequent maintenance [44]
Uniform water and nutrients distribution [48] Limited space for root development [48]
High installation cost [45]
Modular systems Trays Easily disassembled for maintenance [57,59] Complex implementation [23]
Increased variety of plants/aesthetic potential
[45,64,71]
Heavier solutions
Controlled irrigation/drainage [55,67] Surface forms limited to trays dimensions
High environmental burden of some materials
[44,71]
High installation cost [45]
Planter tiles Increased variety of plants/aesthetic potential [45] Complex implementation [23]
Attractive design of modules [60] Limited space for root development [60]
Surface forms limited to tiles dimensions [60]
High installation cost
Flexible bags Adaptable to sloped surfaces [62] Complex implementation [23]
Increased variety of plants/aesthetic potential [45] Heavier solutions due to growing media/limited
to buildings maximum load [62]
High installation cost
M. Manso, J. Castro-Gomes / Renewable and Sustainable Energy Reviews 41 (2015) 863–871 869

Modular green facades have variable costs depending on the
materials used, for example a system using galvanized steel can
be 4–8 times more expensive than a system using HDPE. In the
case of LWS the costs are also very dependent on the materials
used and the system complexity, reaching to a cost of 1200 €/m
2
[45]. Indeed the cost depends also on the application process
(considering the surface dimension and accessibility) and main-
tenance needs (e.g., irrigation, nutrients, plants replacement).
Nevertheless, improving the performance evaluation of recent
green wall systems can lead to an increase of their application in
buildings and therefore result in a reduction on their cost.
Importantly, the decision of which green wall system is more
appropriate to a certain project must depend not only on the
construction and climatic restrictions but also on the environ-
mental impact of its components (e.g., energy or water used and
materials recyclability) and associated costs during its entire
lifecycle.
4. Conclusions
The analysis of the most relevant systems in the field of green
wall systems demonstrates that there is a significant evolution in
this field. Some examples either modular or continuous focus on
its lightness, through the application of geotextile and polymeric
materials. This can be very useful with regard to the application of
these systems in buildings rehabilitation [71].
Continuous solutions are often lighter than modular systems.
But most recent developments of green wall systems design
are mostly focused on modular systems, offering advantages of
installation, allowing a rapid coverage of the entire surface, and
simplifying their maintenance, enabling the disassembly and
replacement of each element.
In the field of green wall characteristics, the main concerns are
to find new strategies for a better performance and durability
through the integration of water retention materials, drainage
means and simpler assembly and maintenance processes.
Systems adaptability is still a field of development. New
solutions must focus not only in the application in new buildings
but also in the rehabilitation of existing buildings, introducing
greening in historical areas [17]. Most systems are designed to be
applied in the vertical plan, allowing, in some cases, their
application in inclined plans with some restrictions. Therefore,
green walls must evolve and adapt to different surface forms and
inclinations (e.g., curved, vertical or horizontal surfaces), with the
convenient adaptations [72].
Considering the analysis of different types of green wall
systems, it can be understood that innovation is mostly centered
in the improvement of their design to achieve a better perfor-
mance, during the installation, usage or maintenance processes
[73].
Yet, green walls must evolve to become more sustainable
solutions [74], through the use of materials with less incorporated
energy and CO
2
emissions and the application of climate adapted
plant species with less irrigation needs [73]. Some examples
already show sustainability concerns by using natural or recycled
materials and native plants, integrating water recovery systems
and sensors for water and nutrients minimization.
In fact, continuing to evaluate the contribution of recent green
wall systems to improve buildings performance and comparing
the environmental impact of these systems with other construc-
tion solutions can lead to an increase of their application in
buildings and therefore result in a reduction on these systems cost.
Acknowledgment
This work is integrated in the research project Geogreen
(Project, PTDC/ECM/113922/2009), partially financed by the
Portuguese Foundation for Science and Technology, FCT.
Appendix A. Supporting information
Supplementary data associated with this article can be found in
the online version at http://dx.doi.org/10.1016/j.rser.2014.07.203.
References
[1] Lundholm J. Green roofs and facades: a habitat template approach. Urb
Habitats 2006;4:87–101 .
[2] Sheweka S, Magdy N. The living walls as an approach for a healthy urban
environment. Energy Proc 2011;6:592–9.
[3] GhaffarianHoseini A, Dahlan N, Berardi U, GhaffarianHoseini A, Makaremi N,
GhaffarianHoseini M. Sustainable energy performances of green buildings: a
review of current theories, implementations and challenges. Renew Sustain
Energy Rev 2013;25:1–17.
[4] Zhang X, Shen L, Tam VWY, Lee WWY. Barriers to implement extensive green
roof systems: a Hong Kong study. Renew Sustain Energy Rev 2012;16:314–9.
[5] Saadatian O, Sopian K, Salleh E, Riffat S, Saadatian E, Toudeshki A, et al. A
review of energy aspects of green roofs. Renew Sustain Energy Rev
2013;23:155–68.
[6] Mazzali U, Peron F, Romagnoni P, Pulselli R, Bastianoni S. Experimental
investigation on the energy performance of living walls in a temperate
climate. Build Environ 2013;64:57–66.
[7] Theodoridou I, Karteris M, Mallinis G, Papadopoulos AM, Hegger M. Assess-
ment of retrofitting measures and solar systems' potential in urban areas using
geographical information systems: application to a Mediterranean city. Renew
Sustain Energy Rev 2012;16:6239–61.
[8] Virtudes A, Manso M. Green façades: as a feature in urban design. ICEUBI 2011.
In: International Conference on Engineering. University of Beira Interior,
Covilhã, Portugal; 2011.
[9] Francis R, Lorimer J. Urban reconciliation ecology: The potential of living roofs
and walls. J Environ Manag 2011;92:1429–37.
[10] Schmidt M. Energy saving strategies through the greening of buildings.
The example of the Institute of Physics of the Humboldt University in Berlin
–Adlershof, Germany. Rio 3 –World Climate and Energy Event, Rio de Janeiro,
Brazil; 2003.
Table 2
Summary of green wall systems composition.
System
requirements
Green facades Continuous LWS Modular LWS
Support Cables, ropes, nets, trellis in stainless steel, galvanized
steel, wood, plastic, glass fiber [51–53,67]
Geotextile felts [47,48,64] Galvanized steel, stainless steel, lightweight and/or
flexible polymers, ceramics [54–62]
Growing media Ground soil or vessels filled with substrate [39,51] –Substrate mixture including organic and/or inorganic
compounds [45,47,48,56,58,63,64]
Vegetation Climbing plants (evergreen or deciduous)
[24,30,33,39,42,45,52]
Shrubs, grasses and
perennials [6,64]
Shrubs, grasses, perennials and succulent plants
[6,31,45]
Drainage Vessels with inferior holes [51] –Lateral and inferior holes [54–59,63]
Irrigation Drip line inside vessels [51,60] Drip line on the top of the
wall [47,48,64]
Drip line on top of each module [54–59,63]
M. Manso, J. Castro-Gomes / Renewable and Sustainable Energy Reviews 41 (2015) 863–871870

[11] Bruse M, Thönnessen M, Radke U. Practical and theoretical investigation of the
influence of facade greening on the distribution of heavy metals in urban
streets. 〈http://www.envi-met.com/documents/papers/facade1999.pdf〉; 1999
[accessed 17.01.12].
[12] Pugh T, MacKenzie A, Whyatt J, Hewitt C. Effectiveness of Green infrastruc-
tures for improvement of air quality in urban street canyons. Environ Sci
Technol 2012;46:7692–9.
[13] Rahman A, Yeok F, Amir A. The building thermal performance and carbon
sequestration evaluation for Psophocarpus tetrogonobulus on biofaçade wall
in the tropical environment. World Acad Sci Eng Technol 2011;76:86–94.
[14] Santamouris M. Cooling the cities –a review of reflective and green roof
mitigation technologies to fight heat island and improve comfort in urban
environments. Sol Energy 2014;103:682–703.
[15] Alexandri E, Jones P. Temperature decreases in an urban canyon due to green
walls and green roofs in diverse climates. Build Environ 2008;43:480–93.
[16] Gago EJ, Roldan, Pacheco-Torres R, Ordóñez J. The city and urban heat islands:
a review of strategies to mitigate adverse effects. Renew Sustain Energy Rev
2013;25:749–58.
[17] Virtudes A, Manso M. Green Walls Benefits in Contemporary City. 1-ICAUD. In:
Proceedings of the first international conference on architecture and urban
design, EPOKA University, Tirana, Albania; 2012.
[18] Ichihara K, Cohen J. New York city property values: what is the impact of green
roofs on rental pricing. Lett Spat Resour Sci 2011;4:21–30.
[19] Sadineni S, Madala S, Boehm RF. Passive building energy savings: a review of
building envelope components. Renew Sustain Energy Rev 2011;15:3617–31.
[20] Wong N, Tan A, Tan P, Chiang K, Wong N. Acoustic evaluation of vertical
greenery systems for building walls. Build Environ 2010;45:411–20.
[21] Renterghem T, Hornikx M, Forssen J, Botteldooren D. The potential of building
envelope greening to achieve quietness. Build Environ 2013;61:34–44.
[22] Kohler M. Green facades –a view back and some visions. Urb Ecosyst
2008;11:423–6.
[23] Pérez G, Rincón L, Vila A, González J, Cabeza L. Green vertical systems for
buildings as passive systems for energy savings. Appl Energy 2011;88:4854–9.
[24] Eumorfopoulou E, Kontoleon K. Experimental approach to the contribution of
plant-covered walls to the thermal behaviour of building envelopes. Build
Environ 2009;44:1024–38.
[25] Bass B. Green roofs and green walls: potential energy savings in winter, Report
on Phase 1. Adaptation and impacts research division environment Canada at
University of Toronto Centre for Environment; 2007.
[26] Koyama T, Yoshinaga M,Hayashi H, Maeda K, Yamauchi A. Identification of key
plant traits contributing to the cooling effects of green façades using free-
standing walls. Build Environ 2013;66:96–103.
[27] Cheng C, Cheung K, Chu L. Thermal performance of a vegetated cladding
system on facade walls. Build Environ 2010;45:1779–87.
[28] Ip K, Lam M, Miller A. Shading performance of a vertical deciduous climbing
plant canopy. Build Environ 2010;45:81–8.
[29] Stec W, van Paassen A, Maziarz A. Modelling the double skin façade with
plants. Energy Build 2005;37:419–27.
[30] Pérez G, Rincón L, Vila A, González J, Cabeza L. Behaviour of green facades in
Mediterranean Continental climate. Energy Convers Manag 2011;52:1861–7.
[31] Jim C, He H. Estimating heat flux transmission of vertical greenery ecosystem.
Ecol Eng 2011;37:1112–22.
[32] Goulding J, Lewis J, Steemers T. Energy in architecture. The European Passive
Solar Handbook. Batsford for the Commission of the European Communities;
1993.
[33] Kontoleon K, Eumorfopoulou E. The effect of the orientation and proportion of
a plant-covered wall layer on the thermal performance of a building zone.
Build Environ 2010;45:1287–303.
[34] Yoshimi J, Altan H. Thermal simulations on the effects of vegetated walls on
indoor building environments. In: Proceedings of Building Simulation 2011,
12th Conference of International Building Performance Simulation Associa-
tion, Sydney; 2011.
[35] GhaffarianHoseini A, et al. Sustainable energy performances of green build-
ings: a review of current theories, implementations and challenges. Renew
Sustain Energy Rev 2013;25:1–17.
[36] Zhang X. Going green: initiatives and technologies in Shanghai World Expo.
Renew Sustain Energy Rev 2013;25(78-88):2013.
[37] AA.VV. Guidelines for the Planning, construction and maintenance of green
roofing –green roofing guideline. Bonn: FLL; 2008.
[38] Newton J, Gedge D, Early P, Wilson S. Building Greener: Guidance on the use
of green roofs, green walls and complementary features on buildings. London:
CIRIA; 2007.
[39] Dunnett N, Kingsbury N. Planting green roofs and living walls. Portland/
London: Timber Press; 2008.
[40] Bass B, Baskaran B. Evaluating rooftop and vertical gardens as an adaptation
strategy for urban areas. CCAF Report B1046. Canada: National Research
Council Canada, Institute for Research Canada; 2003.
[41] Peck SW, Callaghan C, Kuhn ME, Bass B. Greenbacks from green roofs: Forging
a new industry in Canada. Status report on benefits, barriers and opportunities
for green roof and vertical garden technology diffusion. Canada: Canada
Mortgage and Housing Corporation; 1999.
[42] Perini K, Ottelé M, Fraaij A, Haas E, Raiteri R. Vertical greening systems and the
effect on air flow and temperature on the building envelope. Build Environ
2011;46:2287–94.
[43] Wong N, Tan A, Chen Y, Chiang K, Sekar K, Tan P, et al. Thermal evaluation of
vertical greenery systems for building walls. Build Environ 2010;45:663–72.
[44] Ottelé M, Perini K, Fraaij A, Haas E, Raiteri R. Comparative life cycle analysis for
green façades and living wall systems. Energy Build 2011;43:3419–29.
[45] Perini K, Ottelé M, Fraaij A, Haas E, Raiteri R. Greening the building envelope,
façade greening and living wall systems. Open J Ecol 2011;1:1–8.
[46] Laurenz J, Paricio I, Alvarez J, Ruiz F. Natural envelope. The green element as a
boundary limit. SB05Tokyo. The 2005 World Sustainable Building Conference,
Tokyo; 2005.
[47] Corradi L. Hydroponic growing system. US 2009/007486 A1; 8 January 2009.
[48] Bribach C. Vertical garden panel. US 2011/0059518 A1; 10 March 2011.
[49] Fukuzumi Y. Plant growing method for greening wall surfaces. US 5579603;
3 December 1996.
[50] Tsai Y. Upright planting apparatus. US 2011/0088318 A1; 21 April 2011.
[51] Yap T, Wong L, Yoong Y, Tan H, Lim H. A plant tray. WO 2011/005216 A1; 2011.
[52] Yap T, Wong L, Yoong Y, Tan H, Lim H. Supporting structure for green building
facade. WO 2011/016777 A1; 2011.
[53] AA.VV. Introduction to Green Walls Technology. Benefits and Design. Green
Roofs for Healthy Cities; 2008.
[54] Urriola H. Vertical wall garden. US 2011/0094153 A1; 2011.
[55] Laurence M, Sabin R. Plant wall and modules for growing plants. US 2011/
0107667 A1; 2011.
[56] Koumoudis S. Green wall planting module, support structure and irrigation
control system. US 2011/0088319 A1; 2011.
[57] Yap T, Wong L, Tan H, Lim H, Palanisamy T, Tan P, et al. A plant housing device.
WO 2011/014124 A1; 2011.
[58] Sichello C. Plant Propagation and Display Panel and Assembly. WO 2010/
031181 A1; 25 March 2010.
[59] Lee A, Sian G, Greaves H. Green Wall System. WO 2010/009505 A1; 28 January
2010.
[60] Taber S. Modular wall planters. US 2011/0016784 A1; 2011.
[61] Deutsch- Aboulmahassine E. Modular wall-mounted plant growing system. US
7627983 B1; 2009.
[62] Fukuzumi Y. Plant growing method for greening wall surfaces. US 5579603;
1996.
[63] Bindschedler P, Lassalle F. Modular greening device for facades, walls or the
like. US 7757436 B2; 2010.
[64] Blanc P. Vertical garden Patrick Blanc. The Vertical garden, from nature to
cities –a botanical and artistic approach by Patrick Blanc; 〈http://www.
verticalgardenpatrickblanc.com/〉[accessed 19.12.11].
[65] Blanc P. Plant culture on vertical surface. FR 2747265 A1; 1996.
[66] Jetson Green. Lush Edible Living Wall in Los Angeles. www.jetsongreen.com/
2010/08/edible-living-wall-los-angeles.html [accessed 28.03.13].
[67] Bindschedler P, Lassalle F. Modular greening device for facades. US 7757436
B2; 2011.
[68] Huet P, Heine L. Modular wall element for growing plants and modular
structure formed by a plurality of modular elements of the aforementioned
type. US 2010/0095584 A1; 2010.
[69] Manso M, Castro-Gomes J, Dinho P, Virtudes A, Delgado F. Modular system
design for vegetated surfaces. A proposal for energy-efficient buildings. BESS-
SB13 CALIFORNIA. Advancing Towards Net Zero, Pomona, California, USA;
2013.
[70] Perini K, Magliocco A. The integration of vegetation in architecture, vertical
and horizontal greened surfaces. Int J Biol 2012;4:79–91.
[71] Gerhardt C, Vale B. Comparision of resource use and environmental perfor-
mance of green wallls with façade greenings and extensive green roofs. SB 10
New Zealand. Te Papa, Wellington; 2010.
[72] Perini K. Retrofitting with vegetation recent building heritage applying a
design tool –the case study of a school building. Front Archit Res
2013;2:267–77.
[73] Manso M, Virtudes A, Castro-Gomes J. Development of a modular system for
vegetated surfaces in new buildings and retrofitting. World Green Roof
Congress, Coperhagen, Denmark; 2012.
[74] Perini K, Ottelé M, Haas E. Vertical greening systems, a process tree for green
façades and living walls. Urb Ecosyst 2013;16:265–77.
M. Manso, J. Castro-Gomes / Renewable and Sustainable Energy Reviews 41 (2015) 863–871 871