Urban Green Infrastructure in Jordan: A Perceptive of Hurdles and Challenges

Abstract

Jordanians live in compact cities with limited green spaces causing several environmental problems that deteriorate the urban quality of life. Many reports and studies demonstrate the benefits of urban green infrastructure (UGI) in overcoming environmental deterioration in compacted cities. Nevertheless, Urban Green Infrastructure is still lagging in many Arab countries, and Jordan is no exception. UGI refers to a strategically planned network of connected greenspace in urban areas, such as green walls, green roofs, urban trees, and hedges. This study employs the concept of UGI with a particular focus on green walls and roofs. Therefore, this research aims to investigate and determine the key barriers that impede the implementation of UGI in Jordan through qualitative and quantitative analysis. The qualitative study aims to elaborate on root causes that hinder the application of UGI. The quantitative part of the study employs a questionnaire survey to rank the significance of each barrier. This study finds that the shortage of irrigation water and the absence of incentive programs by local authorities were the top two barriers that impede the application of UGI in Jordan.

Keywords:

• Urban green infrastructure
• sustainable urban development
• urban Jordan
• Relative Importance Index

Introduction

Urban agglomerations and buildings have played an essential part in human civilization, advancement of life, and economic development (Angelidou, 2015; Choi, 2009; Fang & Yu, 2017). The United Nations (UN) predicts that 60% of the world population will live in cities by 2030 (Cerón-Palma et al., 2012). In the Global South, and particularly in the Arab countries, over 55% live in urban areas, and projections show that urbanization is expected to grow to 67% by 2050 (UN-HABITAT, 2012; Zeadat, 2018, p. ii).

The mushrooming population growth in cities accompanied by little green and open spaces causes a significant environmental threat affecting the health and well-being of urban dwellers (Cerón-Palma et al., 2012; Hossain et al., 2019). Buildings in cities consume more than 30% of total world energy and emit 33% of greenhouse (GHG) emissions (Alawneh et al., 2018, 2019; Ash et al., 2008; Brooks & McArthur, 2019; Choi, 2009; Mahdiyar et al., 2020; Olaleye & Komolafe, 2015; Tewfik & Ali, 2014; Simons et al., 2014). North Americans spend roughly 90% of their time inside buildings (Simons et al., 2014).

Consequently, buildings’ negative impact on the environment has sparked the interest of both researchers and policymakers (Khasreen et al., 2009). A movement toward green buildings, also known as sustainable or high-performance buildings (i.e., green buildings), has emerged to tackle concerns about buildings’ deteriorating environmental impact (Simons et al., 2014). Following the U.S. Environmental Protection Agency (2008), the concept of green buildings refers to the process of prudently using valuable resources (energy, water, and materials) throughout the building process (i.e., siting, design, construction, operation, renovation, and reuse of a building). Green buildings address two aspects of the building process: resource efficiency and the impact of buildings on the environment (Simons et al., 2014). Choi (2009) added that green development efforts should be holistic to consider micro (i.e., site, neighborhood) and macro levels (i.e., regional) and global levels. Accordingly, the built environment and the real estate industry, in particular, have essential roles to play in addressing climate change and establishing sustainable and green development (Alawneh et al., 2019; Albaali et al., 2021; Alkhalidi & Aljolani, 2020; Olaleye & Komolafe, 2015; Saidi et al., 2021; Tewfik & Ali, 2014).

Significant advancements in sustainable building construction and technology have occurred in the last two decades (Simons et al., 2014). For instance, urban green infrastructure (UGI) (i.e., green roofs, green walls) is the technology of converting impervious concrete surfaces into permeable green surfaces (Carter & Butler, 2008; Getter & Rowe, 2006; Subaskar et al., 2018; Vijayaraghavan, 2016). Russo and Cirella (2018) argued that UGI is essential to address detrimental environmental problems in compact cities.

Despite its benefits, the application of UGI in urban Jordan is still in its infancy. With an area of 237.86 km² and a population of 4.090 million in 2017 (Al-Bilbisi, 2019), only 8.694 km² of Amman are green space (Jordan Times, 2019). In other words, Amman’s green space accounts for only 2.5% of the city’s metropolitan area (Al-Zu’bi & Mansour, 2017). According to the World Health Organization, Amman needs to allocate at least 36 km² (ideally 200 km²) of its urban area as green space (WHO, 2012). Accordingly, this research aims to understand the root causes that hinder the adoption of UGI in real estate. This research supports the argument that urban policymakers have a great chance to incorporate green practices into existing building operations and management. Incorporating elements of UGI in existing buildings will accelerate progress in the area of sustainability, as the operation of a building might be even more critical than building design in terms of sustainability (Miller et al., 2010).

The remainder of the paper is organized as follows. The following section provides a brief account of real estate and the status of green buildings in Jordan. The research then defines the concept of UGI. Afterwards, the qualitative side of the research is presented, explaining the main barriers found in the literature that hinder the application of UGI in urban agglomerations. Quantitative data collection method (i.e. questionnaire survey), research methodology, and procedures to ensure research validity and reliability were explained in the following section. The penultimate section highlight research findings and the final section discusses the results.

Jordanian Real Estate Market

The Hashimite Kingdom of Jordan is a Middle Eastern developing country with more than 11 million people (Department of Statistics, Jordan, 2022), with over 80% of urban residents (Alawneh et al., 2018). Jordan has a total land area of 89,297 km², of which 92% is desert or rangeland (Alawneh et al., 2018). The country has a diverse landscape, ranging from the Jordan rift valley in the West to the desert flatlands in the east, with a scattering of modestly high mountains (Ali & Al Nsairat, 2009).

Jordan’s urbanization results from a dramatic population expansion driven by mass immigration and a refugee influx from neighboring countries (Shawabkeh et al., 2019). Amman and Irbid host around 39% and 18% of Jordan’s population, respectively (Zeadat, 2018, p. 355). Amman has witnessed a “phenomenal” urban transformation in the second half of the 20th century (Potter et al., 2009). Amman grew horizontally and vertically within a minimal land area (Beauregard & Marpillero-Colomina, 2011; Potter et al., 2009), hosting 40% of the total housing stock in Jordan (Alnsour, 2015). Al Rawashdeh and Saleh (2006) reported that Amman urban areas doubled 509 times between 1918 and 2002. The Planning Cities, Towns, Villages and Buildings Act of 1966, no.79, with its amendments in 2022, is the legal framework guiding urban Jordan development. The Act determined seven land use categories: residential,¹ car parks, commercial, industrial, office, and mixed-use development. The most common land use zones in urban Jordan are residential, roads, and commercial (see Figure 1). According to Jordan’s Housing and Urban Development Corporation (HUDC), the total number of housing units was 1,395,000, and it has risen to 1,507,322 between 2012 and 2015.²

Figure 1. Ratio of land use zones areas of the city of Irbid in 2017 (Shawabkeh et al., 2019).

Typically, the real estate market is a vital industry and a strong incentive for the growth of emerging economies (Alawneh et al., 2018, 2019; Apanavičienė et al., 2015). The sector is vital to economic progress and the core of environmental and social sustainability (Kongela, 2013). Jordan’s real estate business is regarded as the most lucrative industry in the economy³ (Hamouri, 2020; Zighan, 2016). The Jordanian real estate market boosts economic activity by contributing to GDP, offering job opportunities, and establishing agile investment opportunities (Hamouri, 2020). Jordan’s real estate market contributed 4.4% of the country’s GDP in 2016, amounting to an additional 1,195.8 million Jordanian dinars (JOD) (Alawneh et al., 2018). From (452.3) million Jordanian dinars in 1990 to (1,195.8) million Jordanian dinars in 2015, real estate continued its upward growth trend (Hamouri, 2020).

Jordan has three types of construction projects: public civil projects, specialist trades projects, and housing construction projects (Zighan, 2016). The traditional procurement route (i.e., design-bid-build) is the most construction procurement route in the Jordanian construction industry (Odeh & Battaineh, 2002). The traditional procurement route implies that the owner’s perspective drives construction projects’ strategic vision and future direction (Oyegoke et al., 2009). Property owners use the most common marketing methods to inform people of their proposals, such as real estate speculators, newspapers, social media, and Open Market website (Haddad, 2019). Jordan’s construction methods utilize modern building systems, with concrete, glass, and steel dominating construction materials and technology (Ali & Al Nsairat, 2009).

Most of Jordan’s green buildings were built under the rubric of the Leadership in Energy and Environmental Design (LEED) v2.2⁴ construction standard (Alawneh et al., 2018). LEED is a non-governmental certification scheme that has gained widespread acceptance worldwide (Alawneh et al., 2019). The program contributed to the evolution of a global green building rating system to ensure energy efficiency and reduce buildings’ detrimental effects on the environment (Alawneh et al., 2018). Nevertheless, Jordan has only nine officially certified LEED buildings⁵ (Alawneh et al., 2019).

Urban Green Infrastructure

Reviewing recent studies from academic literature, the application of UGI is becoming increasingly popular across the Global North⁶ (i.e., Canada, United States, United Kingdom, and Europe) (X. Chen et al., 2019; Ismail et al., 2018; Vijayaraghavan, 2016; Zeadat, 2021; Zhang et al., 2012) and in some south Asian countries such as Malaysia and Hong Kong (Chen et al., 2019; Ismail et al., 2018; Zhang et al., 2012).

Although the popularity of UGI in the environmental management lexicon (Ezema et al., 2016), the concept is still fuzzy and subject to multiple interpretations (Wright, 2011). The concept refers to open spaces, parks, natural areas, green buffers, greenbelts, wildlife habitats, wetlands, forest preserves, farmlands, and golf courses. Some researchers link the concept to merely urban green spaces, urban trees, and hedges designed and managed to deliver a wide range of ecosystem services in urban areas (Klemm et al., 2017; Koch et al., 2020; Liberalesso et al., 2020; Zhu et al., 2019). Theoretically, Benedict and McMahon (2002) defined UGI as an urban system of an “interconnected network of green space that conserves natural ecosystem values and functions and provides associated benefits to human populations” (p. 12 cited in Ezema et al., 2016). This research confines the concept of UGI to only green roofs and green walls. This study considered UGI a vegetated surface in infrastructures (i.e., bridges, tunnels, and overpass) buildings such as green walls and green roofs (Koch et al., 2020; Liberalesso et al., 2020).

Green Roof

Green rooftop gardens are one of the most effective green city approaches for mitigating the effects of growing urbanization and compact cities (Hossain et al., 2019; Russo & Cirella, 2018). A planted roof is a specialized roofing system that has specific components and depth installed atop and across a rigid roof structure (Abdin et al., 2018; Al-Zu’bi & Mansour, 2017; Cerón-Palma et al., 2012; Chen et al., 2019; Ezema et al., 2016; Goussous et al., 2015; W. Z. W. Ismail et al., 2010, 2018; Subaskar et al., 2018; Vijayaraghavan, 2016; Zhang et al., 2012). Growing plants on top of buildings is a well-developed technology with ancient roots dating back to the Hanging Gardens of Babylon (Al Jadaa et al., 2019; Al-Zu’bi and Mansour, 2017; Subaskar et al., 2018; Vijayaraghavan, 2016). Green roofs could hold various vegetation types and sizes ranging from grass, trees, moss, flowers, lichen, sedum, shrubs, and bushes (Subaskar et al., 2018). The concept has many terminologies that have been used interchangeably in the literature, such as eco-roofs, living roofs, sky gardens, roof gardens, or skyrise gardens (Ismail et al., 2010; Mahdiyar et al., 2020; Tam et al., 2016). These terminologies point to inserting vegetation on the impervious roof (Mahdiyar et al., 2020; Tam et al., 2016).

Typically, green roofs contain several layers such as vegetation, growing medium (i.e., soil consisting of inorganic matter and organic material), filter fabric supported by a multi-layered waterproofing membrane, root barrier, insulation (i.e., if the building is heated or cooled) and drainage layer (see Figure 2) (Abdin et al., 2018; Goussous et al., 2015; Vijayaraghavan, 2016; Wong & Lau, 2013).

Figure 2. Schematics of different green roof components (Vijayaraghavan, 2016, p. 744).

Broadly, two main types of green roofs can be distinguished in the literature: extensive green roofs and intensive green roofs (Brudermann & Sangkakool, 2017; Cerón-Palma et al., 2012; Goussous et al., 2015; Hossain et al., 2019; Mahdiyar et al., 2020; Rahman et al., 2013; Subaskar et al., 2018; Tam et al., 2016; Wong & Lau, 2013; Zhang et al., 2012). Other researchers added the classification of semi-intensive green roofs (Berardi et al., 2014; Chen et al., 2019; Ismail et al., 2010, 2018; Vijayaraghavan, 2016). A semi-extensive green roof system is an intermediate between extensive and intensive green roofs (X. Chen et al., 2019; Ismail et al., 2010; Vijayaraghavan, 2016; Zeadat, 2021). It resembles the extensive green roof in lighter dead load with a slightly deeper growing medium (soil). Table 1 shows a comparison between both main classifications of green roofs.

Table 1. Classification of green roofs and their main attributes with supporting literature.

Main attributes	Extensive	Intensive	Source
Soil depth	Relatively thin soil layer ranging between 50 mm and 150 mm thick	Deep soil ranging from 200 mm to 2,000 mm thick	Berardi et al., 2014; Brudermann & Sangkakool, 2017; Ismail et al., 2010; Tam et al., 2016; Zhang et al., 2012
Maintenance	Often plants are left to grow spontaneously, assuming self-maintenance of the roof	Ordinary maintenance (i.e., weeding, fertigation, and watering of the plants).	Berardi et al., 2014; Brudermann & Sangkakool, 2017; Hossain et al., 2019; Ismail et al., 2010; Mahdiyar et al., 2020; Tam et al., 2016; Zhang et al., 2012;
Water needs	Limited or no need for regular irrigation	Need for regular irrigation and drainage systems	Berardi et al., 2014; Brudermann & Sangkakool, 2017; Hossain et al., 2019; Tam et al., 2016
Dead load on supporting structure	Lightweight (80–150 kg/m^2)	More significant weight loading (300–1000 kg/m^2) that requires rigorous structural design	Berardi et al., 2014; Brudermann & Sangkakool, 2017; Chen et al., 2019; Hossain et al., 2019; Ismail et al., 2010; Mahdiyar et al., 2020; Nelms et al., 2005; Rahman et al., 2013; Tam et al., 2016
Capital cost	Relatively inexpensive (US$52 to US$128 per m^2)	Relatively higher upfront cost (US$128 to US$650 per m^2)	Chen et al., 2019; Hossain et al., 2019; Hui, 2010; Mahdiyar et al., 2020; Tam et al., 2016; Zhang et al., 2012
Suitability	Suitable for building retrofitting due to their lower weight. Also, it is recommended for roofs ranging from 0 to 30% slope	Suitable for newly constructed buildings	Ismail et al., 2010; Mahdiyar et al., 2020; Tam et al., 2016
Accessibility	Usually no access for recreation or other uses due to the unavailability of adequate infrastructure.	Often visually and physically accessible for recreational purposes or as an outdoor open space	Hossain et al., 2019; Mahdiyar et al., 2020; Rahman et al., 2013; Tam et al., 2016
Utilization	Limited for maintenance purposes or thermal insulation purposes	Diverse roof utilization (i.e., for recreation, growing food, open space), especially in cities with limited green spaces. It could simulate wildlife growth and develop a more complex ecosystem.	Hossain et al., 2019; Ismail et al., 2010; Tam et al., 2016
Types of planted vegetation	Can support only small and self-generative plants such as cactuses, sedums, small grasses, herbs, flowers, and herbaceous plants with a shallow rooting system	Greater diversity of plants’ sizes and could accommodate trees.	Berardi et al., 2014; Brudermann & Sangkakool, 2017; Hossain et al., 2019; Mahdiyar et al., 2020; Rahman et al., 2013; Tam et al., 2016; Zhang et al., 2012
Thermal insulation	Enhancement of roof thermal insulation u-value.	Enhance insulation properties	Ismail et al., 2010; Tam et al., 2016
Aesthetics	It may be visually unattractive due to limited maintenance, especially in dry and hot seasons.	It can be made very attractive	Ismail et al., 2010; Tam et al., 2016

Green Wall

The second element of UGI is the green wall. Green walls are often referred to it as vertical greening systems (Koch et al., 2020) or façade-integrated greenery (see Figure 2) (Andric et al., 2020). Similar to green roofs, green walls have been used for centuries since the Hanging Gardens of Babylon and in the Roman and Greek Empires (Collins et al., 2017; Köhler, 2008). The green walls have been used to enhance thermal insulations and for esthetical purposes (Andric et al., 2020). Compared to green roofs, vegetation in a green wall is installed vertically rather than horizontally on the building wall. Plants are installed within planter boxes inserted into the wall or in a supporting structure (see Figure 3) (Andric et al., 2020; Azkorra et al., 2015; Collins et al., 2017; Romanova et al., 2019). Compared to other UGI elements, green walls have a higher potential to be applied due to the availability of wall surfaces (vertical surfaces are more prominent than roof area) (Andric et al., 2020; Koch et al., 2020). Moreover, technical problems are less apparent in green walls than in green roofs (Koch et al., 2020).

Figure 3. Schematics of different green wall components (http:perperwww.denory-gw.com).

Generally speaking, there are two types of green walls according to their growing type: living wall systems (LWS) (see Figures 3 and 4) and green facades (GF) (see Figure 4) (Cameron et al., 2014; Chiquet et al., 2013; Collins et al., 2017; K¨ohler, 2008 cited in Koch et al., 2020). Some researchers added biowalls as a third designation (Cameron et al., 2014). Biowalls are used indoors to improve indoor air quality and control humidity. Green facades are the simplest and the cheapest form of green walls where self-adhering climbing plants (creepers) rooting in the soil cover a vertical surface by allowing them to grow freely (Andric et al., 2020; Chiquet et al., 2013). On the one hand, covering the desired vertical area may take a long time, but it requires less maintenance. LWS, in contrast, are costlier and require more significant maintenance efforts (Cameron et al., 2014; Koch et al., 2020). LWS requires installing many cells or compartments (geotextile felts) along steel structural elements attached to a wall. Each cell is then filled with soil, and vegetation is planted accordingly. Furthermore, an artificial irrigation system is needed to reach the vegetation and supply sufficient water and nutrients. Contrary to GF, the end product can be seen immediately, but the installation cost and maintenance are much higher than GF (Perini & Rosasco, 2013 cited in Koch et al., 2020; see Figure 5).

Figure 4. Living green wall module, with plants and empty (Romanova et al., 2019, p. 90).

Figure 5. Direct green façade (Koch et al., 2020, p. 2).

Advantages and Benefits of UGI

There is a plethora of discussion in the academic literature on environmental planning on the variety of benefits that UGI could bring to the urban context (Choi, 2009; Hossain et al., 2019; Subaskar et al., 2018; Zeadat, 2021) (see Table 2). Researchers argue that the development of UGI in cities runs in parallel with sustainable urban development goals, including the economic, social, and environmental dimensions (Al-Zu’bi & Mansour, 2017). Generally speaking, UGI has been used extensively in the developed countries of the West to mitigate the negative impacts of urban growth and achieve more resilient and sustainable cities (Ding & Knaap, 2002; Liberalesso et al., 2020; Russo & Cirella, 2018).

Table 2. Advantages of UGI with its supporting literature barriers that hinder the adoption of UGI in urban areas.

Advantages per supporting reference	Supporting reference(s)
Improve thermal insulation of building	Abdin et al., 2018; He et al., 2020; Al Jadaa et al., 2019; Al-Zu’bi & Mansour, 2017; Azkorra et al., 2015; Berardi et al., 2014; Brudermann & Sangkakool, 2017; Cameron et al., 2014; Chen, 2013; Chen et al., 2019; Chiquet et al., 2013; Coma et al., 2017; Ezema et al., 2016; Goussous et al., 2015; Hossain et al., 2019; Ismail et al., 2012; Khan & Asif, 2017; Koch et al., 2020; Liberalesso et al., 2020; Mahdiyar et al., 2020; Rahman et al., 2013; Sangkakool et al., 2018; Vijayaraghavan, 2016; Wong & Lau, 2013; Zhang et al., 2012.
Mitigate stormwater runoff in urban areas	Abdin et al., 2018; Al Jadaa et al., 2019; Al-Zu’bi & Mansour, 2017; Azkorra et al., 2015; Berardi et al., 2014; Brudermann & Sangkakool, 2017; Cameron et al., 2014; Carter & Fowler, 2008; Chen, 2013; Chen et al., 2019; Chiquet et al., 2013; Ezema et al., 2016; Hossain et al., 2019; Z. Ismail et al., 2012; Koch et al., 2020; Rahman et al., 2013; Sangkakool et al., 2018; Subaskar et al., 2018; Vijayaraghavan, 2016; Zhang et al., 2012.
Enhancing ecological and biodiversity	Al Jadaa et al., 2019; Andric et al., 2020; Azkorra et al., 2015; Berardi et al., 2014; Brudermann & Sangkakool, 2017; Cerón-Palma et al., 2012; Chiquet et al., 2013; Collins et al., 2017; Ezema et al., 2016; Hossain et al., 2019; Ismail et al., 2010; Ismail et al., 2012; Koch et al., 2020; Liberalesso et al., 2020; Mahdiyar et al., 2020; Zhang et al., 2012.
Good stormwater quality in urban areas	Hossain et al., 2019; Vijayaraghavan, 2016.
Health and well-being of citizens of urban areas	Brudermann & Sangkakool, 2017; Ezema et al., 2016; Ismail et al., 2010; Liberalesso et al., 2020; Mahdiyar et al., 2020.
Reduce air pollution in urban areas	Al Jadaa et al., 2019; Berardi et al., 2014; Brudermann & Sangkakool, 2017; Cameron et al., 2014; X. Chen et al., 2019; Chiquet et al., 2013; Ezema et al., 2016; Hossain et al., 2019; Ismail et al., 2010; Koch et al., 2020; Mahdiyar et al., 2020; Rahman et al., 2013; Sangkakool et al., 2018; Subaskar et al., 2018; Vijayaraghavan, 2016; Zhang et al., 2012.
Reducing urban heat island	Al Jadaa et al., 2019; Al-Zu’bi & Mansour, 2017; Andric et al., 2020; Berardi et al., 2014; Brudermann & Sangkakool, 2017; Cameron et al., 2014; Chen et al., 2019; Ezema et al., 2016; Hossain et al., 2019; Ismail et al., 2012; Koch et al., 2020; Liberalesso et al., 2020; Mahdiyar et al., 2020; Sangkakool et al., 2018; Subaskar et al., 2018; Tam et al., 2016; Vijayaraghavan, 2016; Wong & Lau, 2013; Zhang et al., 2012.
Increase property value	Berardi et al., 2014; Liberalesso et al., 2020; Mahdiyar et al., 2020; Rahman et al., 2013.
Providing career opportunities	Chen et al., 2019.
Extending roof life	Berardi et al., 2014; Vijayaraghavan, 2016.
Social benefits (i.e., recreational space)	Ismail et al., 2010; Koch et al., 2020; Mahdiyar et al., 2020; Rahman et al., 2013.
Improving the acoustical characteristics of the surrounding environment	Azkorra et al., 2015; Berardi et al., 2014; Brudermann & Sangkakool, 2017; Cameron et al., 2014; Chiquet et al., 2013; Collins et al., 2017; Ezema et al., 2016; Hossain et al., 2019; Ismail et al., 2010; Ismail et al., 2012; Koch et al., 2020; Liberalesso et al., 2020; Vijayaraghavan, 2016
Improves aesthetics	Al-Zu’bi & Mansour, 2017; Brudermann & Sangkakool, 2017; Cameron et al., 2014; Chen, 2013; Chen et al., 2019; Collins et al., 2017; Ezema et al., 2016; Goussous et al., 2015; Ismail et al., 2010; Ismail et al., 2012; Khan & Asif, 2017; Rahman et al., 2013; Subaskar et al., 2018; Vijayaraghavan, 2016; Wong & Lau, 2013

While green buildings are rapidly gaining traction in most developed countries, the concept and practice of sustainable construction have yet to establish ground in most developing economies (Olaleye & Komolafe, 2015). Understanding and defining root causes is essential to overcoming barriers that hinder the adoption of UGI in urban areas (Ezema et al., 2016; Subaskar et al., 2018; Vijayaraghavan, 2016). This section aims to present and discuss barriers that hinder UGI application found through a review of relevant literature.

Economic and Fiscal Barriers

The economic and fiscal barrier is the first and foremost barrier that is mentioned extensively in the literature (Albaali et al., 2021; Al Jadaa et al., 2019; C. F. Chen, 2013; X. Chen et al., 2019; Liberalesso et al., 2020; Mahdiyar et al., 2020; Olaleye & Komolafe, 2015; Sangkakool et al., 2018; Tewfik & Ali, 2014; Vijayaraghavan, 2016; Wong & Lau, 2013). High installation and construction cost, compared to conventional roofs, has been reported by many researchers as the most significant barriers to the adoption of UGI in urban areas (Albaali et al., 2021; Al Jadaa et al., 2019; Chen, 2013; X. Chen et al., 2019; Liberalesso et al., 2020; Mahdiyar et al., 2020; Olaleye & Komolafe, 2015; Sangkakool et al., 2018; Tewfik & Ali, 2014; Vijayaraghavan, 2016; Wong & Lau, 2013). UGI installation costs could be burdensome for some building owners for three main reasons (Brudermann & Sangkakool, 2017; Cerón-Palma et al., 2012; Chen et al., 2019; Ezema et al., 2016; Mahdiyar et al., 2020).

Firstly, the additional cost of design: This includes architectural landscape design and structural design cost of an intensive green roof or living green walls (Brudermann & Sangkakool, 2017; Ngan, 2004; Ulubeyli & Arslan, 2017; Chen et al., 2019). Landscape design is required in the application of UGI to determine the types and places of vegetation to be used in UGI (Zeadat, 2021). Also, specific structural design is essential for intensive green roofs due to the heavy dead load of soil and live loads (i.e., foot traffic from public use) on building structures.

Secondly, the additional construction cost (Hou & Zhang, 2011; Zhu et al., 2009). Construction cost includes the costs for vegetation (trees, bushes, shrubs) and the costs associated with the trained and well-experienced workforce requirement due to installation complexity. Also, the additional construction cost includes construction material, necessary layering, and supporting infrastructure (Brudermann & Sangkakool, 2017; Cerón-Palma et al., 2012; Mahdiyar et al., 2020).

Thirdly, operation and maintenance costs. Generally speaking, the lifecycle cost depends on the type of UGI: extensive or intensive green roof, living wall system or green facades. Intensive and semi-intensive green roofs and living walls need additional maintenance, administration, and operation (Brudermann & Sangkakool, 2017; Chen et al., 2019; Hou & Zhang, 2011; Tewfik & Ali, 2014; Ulubeyli & Arslan, 2017; Vijayaraghavan, 2016). It is worth adding disposal costs at the end of the roof’s lifetime, including dismantling and removing multiple layers and transporting them to landfills (Vijayaraghavan, 2016). Chen et al. (2019) and Ismail et al. (2012) described maintaining intensive or semi-intensive green roofs as a tedious and complicated task. Typically, UGI requires frequent drainage checks, pesticides, grass cuts, and removing dead or undesired plants may be necessary. Also, fertilizers and irrigation are often needed in regions with long, hot, and dry summer seasons (Chen et al., 2019; Mahdiyar et al., 2020; Sangkakool et al., 2018; Vijayaraghavan, 2016).

Building’s Primary Stakeholder Perception

Generally, primary stakeholders in construction projects are driven by economics, not altruism, when investing in green real estate (Miller et al., 2010; Olaleye & Komolafe, 2015).⁷ Primary stakeholders are more concerned about the cost of retrofitting or installing UGI elements in buildings and how this would affect their bottom line. The conservative attitude of real estate developers and building owners in developing nations would result in minimal interest in implementing UGI (Olaleye & Komolafe, 2015). New construction processes, alternative technologies, materials, material recycling, waste management, and green building systems are rarely kept by contractors and builders in developing nations (Tewfik & Ali, 2014).

Primary stakeholders have a strong influence on decisions related to the adoption of new construction technology (Choi, 2009). On the supply side, primary stakeholders bring a wide range of green building design techniques and construction approaches to the market, making green real estate development appealing to the private sector (Simons et al., 2014). On the demand side, owners consider investing in green real estate for various economic, productivity, environmental, and social benefits (Simons et al., 2014, 2017; Zeadat, 2021). Therefore, their perception and acceptance are critical in applying UGI. It is worth mentioning that lack of interest and support is to be found in potential adopters and other building primary stakeholders due to limited awareness and knowledge of the benefits of UGI (see Table 2) (Brudermann & Sangkakool, 2017; Chen et al., 2019; Ezema et al., 2016; Ismail et al., 2018; Mahdiyar et al., 2020; Wong & Lau, 2013).

Absence of Incentives Policies

Five central incentive policies have been used worldwide to promote the adoption of UGI (Zeadat, 2021). These are indirect and direct financial incentives policies, obligations by law, supporting scientific research and granting context-based sustainability certificates (Zeadat, 2021). Lack of political support offered by the central government and the absence of suitable legislation at the local level is considered one of the top barriers to UGI implementation (Al-Zu’bi & Mansour, 2017; Brudermann & Sangkakool, 2017; Ezema et al., 2016; Ismail et al., 2018; Mahdiyar et al., 2020). Vijayaraghavan (2016) believes that policymakers have a vital role in the success of UGI by enacting legislation that promotes the application of UGI. Urban policymakers have the power to clear common doubts and the ability to issue exemptions to reduce building fees and taxes.

Logistical Barrier

Many researchers have reported logistical shortcomings as a barrier that hinders the application of UGI in cities of developing nations (Ismail et al., 2018; Mahdiyar et al., 2020; Brooks & McArthur, 2019). Logistical barrier entails the unavailability of ad-hoc construction material in the local market or/and limited vegetation suitable to the climatic condition of the region. However, Bond and Perrett (2012) and Shen et al. (2017) argued that logistical shortcomings have a minimal impact, and thus this barrier is considered insignificant in many studies (cited in Brooks & McArthur, 2019, p. 137).

Availability of Roof Space

Many researchers stressed the unavailability or limited roof space as a barrier to adopting green roofs (Cerón-Palma et al., 2012; Mahdiyar et al.,2020; Vijayaraghavan, 2016; Wong & Lau, 2013). In addition to the building’s multi-ownership hurdle, applying a green roof might constrain the usage of Photovoltaic (PV) solar panels, water tanks, and HVAC utilities on rooftops.

Shortage of Irrigation Water

Researchers highlighted the difficulty of using UGI in hot and dry regions in most Arab cities (Attia & Mahmoud, 2009; Schweitzer & Erell, 2014). Harsh climatic conditions and low precipitations in most Arab urban areas make it difficult to adopt intensive green roofs and LWS. Moderate to high levels of precipitations are essential to the success and durability of UGI (Ascione et al., 2013; Berardi et al., 2014; Mahdiyar et al., 2020; Tam et al., 2016). Andric et al. (2020) and Mahdiyar et al. (2020) argued the impact of global warming on the durability and sustainability of vegetation planted on green walls and green roofs due to prolonged and frequent heat waves.

Risk of Damages to Buildings

Green walls and green roofs have often been stigmatized as destructive to building envelopes and impaired building structures and utilities (Chen et al., 2019; Shafique et al., 2018; Tabatabaee et al., 2019). For instance, climbing plants on a green façade have damaged mortar and brick surfaces caused by the plant attachment mechanism (Andric et al., 2020; Chen et al., 2019; Chiquet et al., 2013). Also, concerns associated with intensive green roofs include possible damages resulting from erosion, clogged drainage layers, and filter layer leakage. It has been reported that the roots of invasive trees planted on top of a green roof could cause damage to the root barrier layer, causing water leakage to buildings (Brudermann & Sangkakool, 2017; Ismail et al., 2010; Sangkakool et al., 2018). Leaking problems in green roofs are difficult to identify and more expensive to repair (Ismail et al., 2012). Conventionally, contractors identify leaking in green roofs by removing a large amount of growing media to expose the membrane to locate the leak (Ismail et al., 2012).

Moreover, researchers listed fire risk (tall and dried grasses are often considered a fire hazard), climate and PESTs, and weed spread as concerns over the safety of buildings among property owners in case of improper management and lack of inspection on green roof systems, particularly in multi-ownership properties (Chen et al., 2019; Rahman et al., 2013; Subaskar et al., 2018).

Absence of UGI Construction Codes and Standards

A building code is a set of rules that establish built items’ requirements in construction projects. Building codes and standards are often designed to fit the nature of conventional buildings (Choi, 2009). Generally, the construction industry provides limited technical standards or specifications for green buildings (Chen et al., 2019; Tewfik & Ali, 2014; Wark & Wark, 2003; Zhang et al., 2012). Without established and recognized standards and codes, the benefits of UGI cannot be fully appreciated (Wark & Wark, 2003). The absence of local code or technical guidelines hinders the practical and precise application of UGI elements in buildings (Hui, 2010). Contractors and consultants alike may be reluctant to adopt elements of UGI in their projects due to a lack of consolidated standards and regulations for designing and installing green roof systems. The lack of consolidated standards and regulations for designing and installing green roof systems is associated with the limited number of research and studies in this area (Al Jadaa et al., 2019).

Inadequate Research and Knowledge Gap

One of the most noted hurdles to UGI application is the lack of reliable performance and cost-benefits analysis information of green features (Choi, 2009). Without this information, primary stakeholders will find it difficult to justify the often-higher upfront cost of UGI (Choi, 2009). The lack of scientific data implies that primary stakeholders are likely to have concerns about UGI results and benefits (Olaleye & Komolafe, 2015). Knowledge gab is often associated with the dearth of adequate scientific research. The dearth of local research on practical UGI design issues, particularly in developing countries, undermines the evolvement of technical codes for UGI systems (Al Jadaa et al., 2019; Hui, 2010). The main obstacle that impedes the advancement of scientific research is the lack of scientific data and simulation models (Cerón-Palma et al., 2012; Ismail et al., 2018; Mahdiyar et al., 2020; Sangkakool et al., 2018).

Unavailability of Skilled Labor or Qualified Contractors

A critical barrier is a lack of experience and qualified human resources for either UGI design, implementation, or maintenance (Al Jadaa et al., 2019; Chen et al., 2019; Ezema et al., 2016; Hossain et al., 2019; Mahdiyar et al., 2020). The unavailability of qualified architects and construction firms would elongate the project schedule (Choi, 2009). Delays frequently result in increased risks and cost overruns, which many developers would want to avoid, given their limited budgets and timelines (Choi, 2009). Developing nations often face the limited availability of skilled labor, causing a cumbersome growth of UGI in the building industry (Cerón-Palma et al., 2012; Ismail et al., 2018; Mahdiyar et al., 2020; Subaskar et al., 2018). A lack of professionalism and knowledge gap might lead to poorly implemented green roof projects and discredit green roofs and green walls among the building construction community and the public (Sangkakool et al., 2018).

Research Design

This research is an exploratory study. It incorporates both qualitative and quantitative research strategies to enhance the validity and reliability of research findings (i.e., triangulation) (see Table 3) (Okopi, 2021). Six steps have been followed to justify and validate research results (see Table 3).

Table 3. Sequential diagram of studies methodologies.

Step 1	Identifying barriers to UGI application
Step 2	Questionnaire survey preparation
Step 3	Questionnaire distribution and collection of feedback
Step 4	Analysis of data using RRI. and Cronbach’s alpha
Step 5	Discussion of survey results
Step 6	Conclusion and recommendations

In the beginning, an extensive literature review identified barriers to adopting UGI in urban areas. Secondary data were gathered from academic articles, textbooks, published journals, and research books of conference proceedings. However, the identified barriers may not apply to the Jordanian context since it is prone to differences in legislative, operational, and cultural issues (Brudermann & Sangkakool, 2017; Hossain et al., 2019; W. Z. W. Ismail et al., 2018; Liberalesso et al., 2020; Mahdiyar et al., 2020). Therefore, it is fundamental to engage well-informed Jordanian consultants and contractors to evaluate barriers to UGI implementation. A self-administered survey was conducted between November and December 2021 (see Table 4). Each question in the questionnaire was phrased and checked for clarity of expression. In order to avoid ambiguity and ensure objectivity, each question was available in both Arabic and English. Before being distributed, a pilot survey was conducted with ten selected contractors and consultants to enhance the integrity and clarity of the questionnaire. Feedback from the pilot survey was reflected in the design before the final distribution.

Table 4. Research questionnaire.

Barriers	Not important	Slighlty important	Moderately important	Strongly important	Extremely important
Additional cost of design (structural and architectural design)	□	□	□	□	□
Additional cost of construction materials and plants	□	□	□	□	□
Lifecycle cost (i.e., operation, maintenance, disposal)	□	□	□	□	□
Weak public appreciation	□	□	□	□	□
Lack of interest and support by building owners	□	□	□	□	□
Absence of incentive programs by municipalities	□	□	□	□	□
Lack of political support offered by the central government	□	□	□	□	□
Unavailability of ad-hoc construction material in the local market	□	□	□	□	□
Lack of plants for green walls and green roofs convenient to Jordan’s climate	□	□	□	□	□
Limited availability of roof space	□	□	□	□	□
Irrigation water shortage	□	□	□	□	□
Hot and dry climate of Jordan during most months of the year	□	□	□	□	□
Unavailability of skilled labor and contractors to construct green roofs or green walls	□	□	□	□	□
Dearth of local scientific research	□	□	□	□	□
Risk of damages to the building (water leakages, structural failure, fire)	□	□	□	□	□
Absence of industry codes and regulations	□	□	□	□	□

Research respondents were asked to give opinions on each barrier’s relative significance according to the Jordanian context. The Likert scale has been used to collect consultants’ and contractors’ opinions in value of 1 (not important) to 5 (extremely important) for the significance of barriers. A questionnaire survey has been distributed through several methods like a hard copy, email, Google forms and in-person interviews. A total of 120 consultants and 83 contractors registered in the Jordanian Engineers Syndicate and Jordanian Contractors Association, respectively, completed the research questionnaire, out of which 65.02% had more than 20 years of experience working in either building design or construction in Jordan.

Data are then gathered and analyzed through a non-parametric technique called the Relative Importance Index (RRI). RRI is a reliable technique for analyzing structured questionnaires with ordinal measurement of attitudes (Abraham, 2003; Dixit et al., 2019; Durdyev et al., 2012; Huo et al., 2018; Sodangi et al., 2014). The importance of RRI lies in the ability to “[find] the contribution a particular variable makes to the prediction of a criterion variable both by itself and in combination with other predictor variables” (Somiah et al., 2015, p. 120). This study adopted Akadiri’s (2011, p. 239) classification guide of RRI to determine the level of impact for each barrier on the adoption of UGI in urban Jordan (see Table 5).

Table 5. Classification guide to determine the importance level of RII.

RRI values	Importance level
0.8 ≤ RII ≤ 1	High (H)
0.6 ≤ RII < 0.8	High–medium (H-M)
0.4 ≤ RII < 0.6	Medium (M)
0.2 ≤ RII < 0.4	Medium–low (M-L)
0 ≤ RII < 0.2	Low

Validity and Reliability of the Quantitative Study

When items form a scale (i.e., Likert scale), it is vital to ensure their reliability (Jarkas et al., 2015; Pallant, 2013, chapter 9; Shah et al., 2021; Tsiga et al., 2016). Reliability of scale is used to “calculate the stability of a scale from the internal consistency of an item by measuring the construct” (Santos, 1999, cited in Tsiga et al., 2016, p. 6). The alpha coefficient ranges from 0 to 1, whereby the greater the value is considered more reliable for the study (Shah et al., 2021; Nunnaly, 1978 cited in Jarkas et al., 2015). A minimum value of 0.5 is considered to validate the consistency and reliability of the data collected (Shah et al., 2021), while others believe that the Cronbach alpha coefficient should be above .7 (Huo et al., 2018; Kazaz et al., 2016). This study reported the Cronbach alpha coefficient of .781 for the scale measuring barriers. Accordingly, the current study reported an excellent Cronbach alpha coefficient, thus ensuring the scale’s internal consistency.

Pearson’s correlation coefficient was employed to ensure the research results’ validity. The Pearson correlation value of the twelve items exceeds the set critical value of .13, which is significant (less than the p value of .05).

It is worth mentioning that this study employed the Spearman Rank Correlation coefficient to test the strength of agreement between the rankings of contractors and consultants for each barrier (Odeh & Battaineh, 2002). In other words, it reveals if there is agreement or disagreement among contractors and consultants on their respective rankings to barriers. The higher value of r_s (approaching 1) indicates a strong agreement between contractors and consultants to rank the causes of delays. Microsoft Excel was used to calculate Spearman correlation coefficients, which resulted in the value of .5941. According to Cohen (1988, pp. 79–81), this indicates a very good agreement between the two groups.

Furthermore, the association among the rankings of consultants and contractors is checked by hypothesis testing at a significance level of 95%, by which the p value is equal to .05. This study calculated the p value using Excel by implementing the TDIST function. The reported p value in this study is equal to .015, meaning that the null hypothesis is rejected and a significant positive correlation between the ranks of contractors and consultants is demonstrated.

Results and Discussion

Research participants (96.7%) believe that urban Jordan needs to apply UGI and would like to see more green roofs and walls as part of building facilities. However, 85.85% of participants were optimistic and believed that UGI is applicable in Jordan. Research findings reveal that lack of irrigation water is the most critical barrier that hinders UGI application in urban Jordan, while the lack of plants for UGI convenient to Jordan’s climate is considered by research participants as the least effective barrier (see Table 6).

Table 6. Barriers that hinder UGI application in urban Jordan with descriptive statistics.

SN	Factor	Mean	Minimum	Maximum	Standard deviation	Overall RII	RII level of importance	Overall rank	Consultant’s RII	Consultant rank	Contractor’s RII	Contractor rank
1	Irrigation water shortage	4.33	1	5	.959	0.8669	High	1	0.8764	1	0.8539	3
2	Absence of incentive programs by municipalities (i.e., local government)	4.19	2	5	.877	0.8377	High	2	0.7967	4	0.8943	1
3	Lack of political support offered by the central government	4.09	1	5	.854	0.8179	High	3	0.7902	6	0.8561	2
4	Lack of interest and support by building owners and real estate developers	4.01	1	5	1.115	0.8018	High	4	0.8130	3	0.7865	6
5	Lifecycle cost (i.e., operation, maintenance, disposal)	3.98	1	5	.887	0.7962	High–medium	5	0.8390	2	0.7370	7
6	Absence of industry code and regulations	3.97	1	5	1.085	0.79433	High–medium	6	0.7804	8	0.8134	4
7	Dearth of scientific local research	3.81	1	5	1.056	0.7622	High–medium	7	0.7300	12	0.8067	5
8	Risk of damages to building (water leakages, structural failure, fire, …etc.)	3.80	1	5	1.085	0.7594	High–medium	8	0.7951	5	0.7101	10
9	Additional cost of construction materials and plants	3.75	1	5	1.204	0.7490	High–medium	9	0.7821	7	0.7033	12
10	Hot and dry climate of Jordan during most months of year	3.67	1	5	1.194	0.7349	High–medium	10	0.7463	11	0.7191	9
11	Additional cost of design (structural and architectural design)	3.66	1	5	.858	0.7311	High–medium	11	0.7756	9	0.6696	13
12	Weak public appreciation	3.65	1	5	1.137	0.7292	High–medium	12	0.7284	13	0.7303	8
13	Unavailability of skilled Labor and contractors to construct Green roofs or green walls	3.54	1	5	1.149	0.7075	High–medium	13	0.7560	10	0.6404	16
14	limited availability of roof space	3.51	1	5	1.059	0.7028	High–medium	14	0.6991	15	0.7078	11
15	Unavailability of ad-hoc construction material in the local market	3.44	1	5	1.140	0.6886	High–medium	15	0.7073	14	0.6629	14
16	Lack of plants for green walls and green roofs convenient to Jordan’s climate that is available in the local market	3.29			.968	0.6584	High–medium	16	0.6601	16	0.6561	15

Irrigation Water Shortage

Lack of irrigation water ranked first by both consultants and contractors. Water shortage is a severe challenge in Jordan, a problem that severely impacts every business that depends on water to continue operating and succeeding (Alawneh et al., 2018; Albaali et al., 2020; Ali & Al Nsairat, 2009; Hadadin et al., 2010). Jordan’s water shortage is the most significant constraint to the country’s growth and development, as water plays an essential role in food production, health, urban resident welfare, survival, and social and economic development (Ali & Al Nsairat, 2009). Jordan is listed among the world’s poorest countries due to the lack of adequate rainfall and scarce natural water resources (Goussous et al., 2015; Hossain et al., 2019). Jordan’s acute water deficit is caused by a scarcity of natural surface water resources and lingering droughts affecting the country (Ali & Al Nsairat, 2009; Al-Zu’bi and Mansour, 2017). Jordan is classified as a semiarid to arid region, with annual rainfall ranging from 134 to 200 mm over 92% of its geographical area (Alawneh et al., 2018), putting Jordan in the category of an absolute water deficit (Ali & Al Nsairat, 2009). Reflecting the climatic condition and scarceness of water resources, a significant issue for Amman landscape maintenance is irrigation water supply (Potter et al., 2009). As a result of population expansion, accessible water resources per capita are expected to decline from less than 160 m³/capita/year to around 90 m³/capita/year by 2025. Karteris et al., (2016) argued the possibility of successfully adopting UGI in deserted and semiarid regions such as the Mediterranean basin. Average precipitations in Amman are as low as 276 mm (Al-Zu’bi & Mansour, 2017) per annum, which is considered very low compared to many European and North American cities that adopted the model of UGI in urban areas. However, Mahdiyar et al. (2020) and Karteris et al. (2016) agreed that the adoption of UGI is possible in the Mediterranean basin. Andric et al. (2020) and Al-Zu’bi and Mansour (2017) suggested the plantation of native plants (dry-tolerant species) and recycling greywater from the building to irrigate green roofs and living green walls. Greywater is waste water from non-toileted plumbing systems such as hand basin, laundry, showers, and kitchen activities and typically account for 65–90% of the domestic wastewater production (Vijayaraghavan, 2016).

Lack of Political Support Offered by Planning Authorities

Although the limited green spaces in urban Jordan, UGI, or other green building elements have not received profound support from local, regional and national governments. As a result of Jordan’s utilitarian approach to governance, local authorities have insufficient incentive programs and movements to encourage green building technology and UGI (Al-Asad & Emtaireh, 2011 cited in Al-Zu’bi & Mansour, 2017). The absence of political support from the central and local governments is more apparent in developing countries as governmental authorities are still unable to apprehend the variety of benefits of UGI. According to Zeadat (2021), indirect financial incentives (i.e., tax reductions, reduction in stormwater utility fee, reduction of interest rate, density bonus) are the most effective incentive policy to promote UGI in Jordan.

Building’s Primary Stakeholder Perception

In order to achieve sustainable development, awareness about the benefits of UGI among primary stakeholders is critical for its application (Rahman et al., 2013). Mahdiyar et al. (2020) argued that building owners are the least informed and experienced about sustainable options among the construction stakeholders. Many research respondents agreed that building owners need to be convinced that the green roof or green walls bring various benefits to buildings per se and their surroundings. For instance, a green roof elongates the life span of the waterproofing membrane, thus saving cost in the long run (Al-Zu’bi & Mansour, 2017; Ismail et al., 2010; Subaskar et al., 2018). Chen et al. (2019) and Goussous et al. (2015) saw that building clients could be convinced through the lifecycle cost-benefit from energy savings and rainwater reuse.

Moreover, the development of UGI is still in its infancy stage, and the public in Jordan may lack knowledge and awareness about the benefits of UGI and its feasibility in Jordan (weak public appreciation). Changing the mentality and perception of primary stakeholders regarding green building technologies is very important to the widespread of green roofs and green walls projects. Although this barrier has been ranked 12th by research respondents, this study argues the necessity of culture cultivation among Jordanians to ensure widespread adoption of green building principles in general and UGI in specific. Without the support from the public, particularly building primary stakeholders, the development of UGI in urban Jordan will be stagnant or cumbersome, leading to distrust among potential adopters. Moreover, this study suggests further research to examine building users’ willingness to pay (WTP)⁸ for green buildings in Jordan.

Economic and Fiscal Barriers

Additional construction cost and the cost of the structural and architectural design of UGI has been ranked the first and most significant barrier in many countries (Al Jadaa et al., 2019; Chen, 2013; Chen et al., 2019; Liberalesso et al., 2020; Mahdiyar et al., 2020; Sangkakool et al., 2018; Vijayaraghavan, 2016; Wong & Lau, 2013). On the contrary, according to the Jordanian context, research respondents ranked the earlier barrier as the 9th most significant hurdle, while the latter ranked 11th. This research demonstrates the erroneous belief that the cost and financial risks of UGI construction outweigh its benefits. Both Kats (2013) and Morris and Langdon (2007) argued that green buildings cost around 2% extra to build than conventional buildings, which is insignificant compared to the benefits of UGI, as demonstrated in empirical investigations. Moreover, Langdon (2007 cited in Miller et al., 2010) examines construction costs in New York City for 38 high-rise residential buildings and 25 commercial interiors, and he noticed that the cost difference for new structures is less than 1%.

Literature highlights many architectural, structural, and mechanical arrangements that need to be considered when designing green roofs or green walls (Chen et al., 2019). Unlike designing the conventional roofing system of reinforced concrete coarse (RCC), which is familiar to most consultants and contractors in Jordan, the concept of UGI is nascent worldwide and requires more sophisticated considerations such as (structural analysis, waterproof engineering, and irrigation design (Chen et al., 2019). Thus a higher design fee is required when designing a green roof or green wall.

In Jordan, maintenance of UGI is another critical barrier that concerns building owners and facility managers in Jordan. Among other economic barriers, operations and maintenance costs have been ranked fifth. Multi-ownership of most of the building’s roofs in Jordan makes it even harder to administer the maintenance cost. The durability of extensive roofs or green living walls requires frequent maintenance to ensure durability.

Inadequate Research and Knowledge Gap

Since each country has its climatic condition and form of urbanization, local research is of utmost importance for the success of green building and UGI (Vijayaraghavan, 2016). The last two decades have witnessed a dramatic increase in the publication rate regarding UGI in the Global North (Tam et al., 2016). In comparison, limited studies have been done from the perspective of the Arab region. For instance, two studies have partially addressed this topic in the Jordanian context (Al-Zu’bi & Mansour, 2017; Goussous et al., 2015), but no research has been found to discover its full potential in Jordan. In order to fill this gap, this study contributes to a more systematic understanding of those factors, which are important constraints that impede the spread of green roofs and green walls in Jordan.

Absence of UGI Construction Codes and Standards

It is of strategic importance to bear in mind the legislative and operational context of the Jordanian built environment for developing context-based UGI standards and guidelines. This study stressed that organizations, municipalities, and countries should develop guidelines, manuals, and codes for green walls and green roofs systems to suit their needs and circumstances. Authorities of Jordan can adopt and adapt codes and standards from counties with well-established systems and a long history of successful UGI implementation. Ismail et al. (2012) and Hui (2010) reported that some countries such as Germany, Canada, Japan, Australia, UAE, UK, and the USA had developed their standards and guidelines concerning green roof and green walls systems.

The “Jordan Green Building Guide” was published in 2013, covering seven areas: green building management, site sustainability, water efficiency requirements, energy efficiency requirements, healthy indoor environment, materials and resources (Tewfik & Ali, 2014). Construction practices and technology in Jordan should implement the aforementioned guiding principles and be culminated into a code. Adopting Jordan Green Building Guide would promote building construction standards and practice, thus delivering a significant shift and reform of building rules. Moreover, Jordan Green Building Guide could play an essential role in laying out a clear path for Jordan’s green building rating system (Albaali et al., 2021).

Risk of Physical Damages to Buildings

Many contractors and consultants comment on water leakage due to improper design and lousy finishing quality. Although still possible, this barrier did not receive much attention and ranked 8th among research respondents. This study agreed with Brudermann and Sangkakool (2017) that any roof would possibly leak, but the risk to building’s structure as a barrier is an issue that belongs to the past and is not very relevant in well-managed construction projects. Proper design and professional installation could avoid structural risk or building water leakages. But if it occurs, modern technology provides specialists with Electric Field Vector Mapping (EFVM)) to locate a leak in the green roof rather than the conventional way of removing the entire area of the growing medium (Ismail et al., 2012). Moreover, many pieces of research prove that some greenery used to cover building façades (e.g., Hedera spp.) protects walls by ameliorating temperature and relative humidity extremes (Sternberg et al., 2010 cited in Chiquet et al., 2013). Extensive green roofs double the life span of the roof system to serve up to 25 years by protecting the waterproof membrane from UV, heat and cold waves, and mechanical damage (Kosareo & Ries, 2007; Vijayaraghavan, 2016).

Availability of Roof Spaces

A quick review of Jordan rooftops shows that most roofs are used for solar panels,⁹ HVAC mechanical equipment, solar water heating, or water tanks. Therefore, green roofs minimize the surface area for solar panels and other devices. This barrier has been ranked 14th among other barriers despite the importance of roof space due to the advancement in technologies that makes it possible to merge both green roofs and Photovoltaic (PV) named Hybrid Photovoltaic (PV)-green roofs (Lamnatou & Chemisana, 2015). Also, studies well documented that the cooler the temperature, the better PV performance (Kaiser et al., 2014). Consequently, green roofs decrease the surface and ambient air temperature through the evapo-transpirative mechanism, thus enhancing PV performance (Vijayaraghavan, 2016).

Logistical Barrier

Most research respondents believe that ad-hoc construction materials and plants for green roofs and green walls are available in the Jordanian market (both barriers ranked 15th and 16th, respectively). The study stressed that various plants in the Jordanian market are suitable for hot and dry climatic conditions and drought tolerance. In addition, most building contractors in Jordan are capable and equipped to offer UGI once Jordanian authorities enact its codes and standards. However, the problem revolves around the limited number of professional landscape architects to advise selecting suitable plants according to green walls or green roofs.¹⁰

Conclusion

This study demonstrates that urban green infrastructure (UGI) has excellent potential to address adverse impacts of urban growth and improve the environmental performance of a building. However, UGI application is limited in developing countries, and Jordan is no exception. There is a lack of understanding of the root causes regarding the limited widespread of UGI in Jordan. This study aims to highlight the main barriers hindering the adoption of UGI in urban Jordan. Accordingly, this study adopted a mixed approach of qualitative and quantitative methods to achieve the research’s primary objective. The qualitative nature implies a content analysis and a critical literature review of relevant journals, articles, reports, and conference proceedings. A total of 16 barriers that hinder the application of UGI were retrieved from the literature. Following this, 214 consultants and contractors filled and ranked each barrier from being not necessary to extremely important. Research results stressed that shortages of irrigation water and water scarcity is the primary and critical barrier that hinders the adoption of UGI in urban Jordan. Grey water recycling in buildings was suggested to overcome this barrier.

Three areas require further development in this study—the first area of improvement related to research design and enhancing the generalizability and validity of research results. Improvement lies in promoting diversity among research respondents to involve a variety of respondents’ backgrounds from academics, city planners, real estate developers, and city council officials, which will yield more profound and richer results. Secondly, and regarding research analysis tools, adopting a fuzzy-based constrained optimization approach would yield more accurate results than the RRI method as a prioritization approach (Mahdiyar et al., 2020). RRI is a conventional type of ranking that provides less accuracy than the fuzzy-based constrained optimization approach (Mahdiyar et al., 2020).

Additional information

Funding

The American University of Madaba has generously funded the publication of this article.

Notes

1 Sixty-nine percent of total housing units take the form of apartment blocks.

2 This is published in a report conducted by Friedrich-Ebert-Stiftung (FES) office in Amman and Jordan’s Royal Scientific Society (RSS) in 2013.

3 Jordan is classed as a lower middle-income country by the United Nations (Alawneh et al., 2018).

4 LEED Version 1.0 was released in 1998. LEED Green Building Rating System Version 2.0 was launched in March 2000 after major revisions and upgrades on Version 1.0. Afterward, LEED issued Versions 2.1, 2.2, and 3.0 in 2002, 2005, and 2009, respectively (Alawneh et al., 2019).

5 The Netherlands embassy in Jordan is Jordan’s first LEED certified building (Saidi et al., 2021).

6 Among this contest, Germany is taking the leadership role in promoting UGI in urban areas (Zeadat, 2021; Zhang et al., 2012). In contrast, UGI in cities of the Global South and the Arab region, in particular, is sparse and needs further development (Attia & Mahmoud, 2009; Blank et al., 2013).

7 According to Kamalirad et al. (2017), business stakeholders, hence building construction, are classified into either primary or secondary stakeholders. Primary stakeholders include building developers, owners and property managers, architects, and construction companies. On the other hand, secondary stakeholders involve but are not limited to non-governmental organizations, activists, communities, and governments, and general societal trends and institutional forces (Waddock et al., 2002).

8 WTP is an indicator that shows a customer’s willingness to pay for a product or service (Njo et al., 2021).

9 Since the vast majority of Jordan’s land is desert, Jordan is considered one of the countries with the highest rates of solar radiation on their lands; the average sunny days account for 300 days per year which is considered a tremendous source of solar energy.

10 According to a study conducted by Friedrich-Ebert-Stiftung (FES) office in Amman and Jordan’s Royal Scientific Society (RSS) in 2013, a limited number of specialists are trained and licensed in green buildings in Jordan.