Perception of Vertical Greening Applications on Historic Buildings

Abstract

The implementation of Vertical Greening Systems (VGS), like green façades, on historic building facades is approached with caution due to concerns regarding material compatibility, visual impact, and potential compromises to cultural significance. However, VGS can offer significant contributions to urban sustainability when integrated with knowledge and care of historic buildings by reducing the urban heat island effect, improving air quality, fostering a green economy, and creating greener environments. These tensions highlight a critical research gap: how can VGS contribute to urban sustainability while respecting the values of historic building façades? This study addresses this gap by exploring professional interest groups’ opinions on implementing VGS on historic buildings, focusing on the perceived benefits and concerns from environmental, social, economic, cultural, legal, and technical aspects. A mixed-methods approach was employed, combining the findings from the literature review with a survey targeting individuals involved in VGS implementations or heritage conservation. The survey included both open- and closed-ended questions. Of the 165 individuals contacted, 83 valid responses were analyzed. Results from the open-ended questions showed that 89% of respondents recognized the environmental benefits of VGS, while 85% raised technical issues, particularly regarding material compatibility. An important insight emerged from comparing open-ended and closed-ended responses: respondents were more likely to acknowledge the benefits of VGS when prompted. This indicates that raising awareness about the use of VGS on historic buildings is essential. The findings offer practical implications for early-stage planning, stakeholder engagement, and the design of heritage conservation policy. They illustrate a need for an informed decision-making process for the integration of VGS onto historic building facades, aligning with conservation ethics and urban sustainability. Preface: This study aims to create a discussion on the potential synergies between vertical greening and historic buildings, with the intention of guiding future conservation strategies to enhance urban sustainability. We do not advocate for vertical greenery as a universal solution, but rather seek to explore under which conditions vertical greening may be compatible with conservation practice. For the purposes of this study, “historic buildings” refer to structures that possess cultural, architectural, or historical significance, whether they are formally protected or informally valued by their communities. We acknowledge that the term may vary in meaning across different national and cultural contexts. Moreover, our analysis focuses on cases where both the vertical greening and historic façades are presumed to be in structurally sound and well-maintained condition.

1. Introduction

Historic buildings are a significant part of the urban fabric in most European cities [1]. In the face of climate change and rapid urbanization, there is a growing need to develop new strategies for adaptation of historic built environments. Rather than viewing historic buildings as mere passive elements to be preserved, we should recognize them as active contributors to wider sustainability efforts, especially given the limited horizontal space available for green initiatives in urban centers. This includes supporting the United Nations’ 2030 Agenda for Sustainable Development, particularly in relation to Goal 11: Sustainable Cities and Communities, Target 11.4 “strengthen efforts to protect and safeguard the world’s cultural and natural heritage”, and Goal 13: Climate Action [2]. UNESCO’s Culture 2030 Indicators further recognize cultural heritage as a cross-cutting enabler across all 17 Sustainable Development Goals, underscoring the potential for historic environments to play a proactive role in sustainability transitions [3]. Nevertheless, any kind of intervention, especially those involving physical alterations to heritage fabric, must be approached with caution. Ensuring compatibility with conservation principles is essential to safeguard the authenticity, integrity, and contextual value of historic sites [4,5,6].

Despite the vast amount of research on urban sustainability and heritage conservation, there are limited studies covering the relationship between nature and historic buildings [7]. In conservation practice, nature has traditionally been perceived as a threat to historic buildings, capable of degrading materials and diminishing aesthetic or historic value through processes like biological colonization and weathering [8,9,10]. These risks often discouraged engagement with nature as a design element. However, a more holistic approach is needed; one that, through conscious planning and context-sensitive design, can unlock opportunities to integrate nature in ways that both respect and potentially enhance heritage values [7].

In dense urban environments where green space is scarce, Vertical Greening Systems (VGSs) can be a viable solution [11]. VGS encompasses green facades and living wall systems. Green facades involve climbing plants growing on building surfaces or support structures, while living walls feature modular vegetation systems with irrigation [12] (Figure 1). In this study, this broad definition was adopted from the literature to encompass both green façades and living wall systems, even though green façades are a more traditional and common type of VGS on historic buildings.

Evaluating the benefits and drawbacks of VGS on historic buildings is a complex process, as it involves not only empirical data but also subjective perceptions shaped by stakeholders’ knowledge, experiences, and expectations [13,14]. Numerous studies have qualitatively analyzed people’s perspectives on the integration of VGS into built environments [15,16,17,18,19,20,21]. However, there is a lack of research specifically addressing the concerns and benefits of implementing VGS on historic buildings.

Moreover, literature suggests that integrating VGS into buildings can provide multiple benefits. Reducing the surface temperature by thermal blanketing [22,23,24,25,26,27,28,29,30], decreasing noise pollution [31,32], improving air quality [17,19,33,34,35,36,37], enhancing biodiversity [38,39,40], managing water through rainwater absorption and purification [41,42,43], reducing the wind speed [25,44,45,46,47], and lowering the energy needs [23,48,49,50,51,52,53,54,55,56] have been put forward as the main environmental benefits. Culturally, studies have shown that VGS brings aesthetic value to building façades [15,18,33,34,57,58,59,60] and strengthens a sense of place [11,61,62]. A study by Thornbush (2013) presents that from the mid-19th to mid-20th century, climbing plants were not only accepted but actively cultivated on historic buildings to celebrate nature as a softening and romanticizing element within architectural compositions [63]. VGS can improve psychological well-being and reduce stress [64,65,66,67] by creating recreational space for people to gather [11] and providing educational opportunities for people to learn about ecology [19,34]. VGS can reduce energy costs, increase property values, and extend building facade lifespans, contributing to long-term cost savings [34,68,69]. Legally, integrating green measures into existing building codes has expanded the legal boundaries and advanced green building standards [70,71] with government initiatives, such as green rating systems, labeling programs, and financial subsidies [37,71,72]. Additionally, cost-effective designs and accessible maintenance strategies facilitate VGS implementation at the community level [73,74]. From a technical standpoint, VGS offers protection against environmental factors such as UV radiation and acid rain, contributing to the preservation of building surfaces [32,69,70,75].

Despite these advantages, VGS also brings various challenges. Environmentally, the potential attraction of pests [76,77,78] and the environmental burden caused by using non-biodegradable materials like PVC, EPDM membranes, and synthetic geotextiles that are used for living wall systems raise concerns [17]. From a cultural standpoint, the integration of vegetation onto historic façades risks obscuring architectural details and undermining material legibility, raising fears of diminished authenticity and irreversible alteration [7,79]. These concerns align with core principles of conservation theory and international charters, which emphasize minimal intervention (Venice Charter, 1964), authenticity (Nara Document, 1994), and context sensitivity (Burra Charter, 2013) [4,5,6]. Therefore, interventions like VGS should comply with these principles and minimize any risk posed to the integrity of the building. Social challenges include allergy risks from certain plant species and the presence of microorganisms [80]. High installation and maintenance costs present economic obstacles [16,18,19,21,33,37,81,82,83]. Lack of funding hinders the widespread adoption of VGS [33], while VGS implementations can lead to gentrification and displacement due to increasing property values [84,85]. Complex regulatory frameworks, inconsistent standards, and political and administrative challenges [21,37,86,87] are significant legal barriers to the adaptation of VGS. While the lack of clear guidelines does not constitute a legal barrier itself, it creates a grey zone for planning decisions, leading to uncertainty in the approval and implementation processes [16,33,88]. Additionally, there is a risk of using VGS to justify denser building developments, which could compromise the intended urban sustainability [17]. From a technical standpoint, challenges are particularly valid in historic settings. VGS may introduce additional structural loads, moisture retention issues, and biofilm growth that threaten the material integrity of historic fabric [21,37,89,90]. Drawing on restoration theory and architectural conservation literature, it is important to ensure the physical compatibility, reversibility, and maintenance of innovative interventions like VGS [91,92,93]. Proper maintenance, in particular, is essential to prevent problems such as uncontrolled plant growth, which can cause material cracks, block gutters, and pose fire hazards due to the accumulation of dried leaves [15,16,21,33,94]. The success of VGS in heritage contexts requires not only technical expertise but also tailored maintenance strategies that are sensitive to the building’s historic character [73]. All these aspects portray how VGS has been discussed in the literature until 2025.

Despite growing interest in VGS within urban sustainability and architectural design, few studies have critically explored their compatibility with historic buildings from a heritage conservation perspective [7,29,95,96,97]. While some recent initiatives, such as English Heritage and the Antwerp Police Codex, have begun to encourage VGS integration on historic buildings and offer implementation or maintenance guidance [98,99], these efforts remain limited in scope. Broader, more consistent frameworks are still needed to guide responsible adaptation in historic contexts. This gap in both academic discourse and policy development highlights that the decisions regarding the VGS implementation on historic buildings are often shaped more by perceptions and inherited assumptions among heritage professionals than by empirical evidence [7]. Therefore, assessing the suitability of VGS requires not only consideration of physical and technical compatibility but also an understanding of professional judgment. This underscores the need for a perception-based approach to examine the diverse values, concerns, and disciplinary tensions surrounding the integration of VGS in historic settings.

To address this issue, the study adopts a perception-driven methodology that centers stakeholder experiences and expectations, rather than relying on technical performance metrics. Responses were collected from 83 professionals across relevant disciplines. The findings are organized into six key thematic dimensions: environmental, social, economic, cultural, legal, and technical, developed through an interdisciplinary evaluation framework grounded in restoration theory and sustainability principles. In doing so, the research addresses two core questions: (1) How do professional interest groups perceive the benefits and concerns of implementing VGS on historic buildings? (2) How consistent are these perceptions across different evaluation dimensions?

2. Methods

This study aims to bridge the fields of urban sustainability and heritage conservation. Therefore, it assesses the integration potentials of VGS to historic buildings not based on physical compatibility but through the lens of perception and professional judgment. To facilitate this, six key aspects were articulated: environmental, social, economic, cultural, legal, and technical (

Table 1. Literature Review Evaluation Framework: Evaluated aspects of the role of VGS in the sustainable conservation of historic buildings.

). This interdisciplinary framework provided the basis for the literature analysis and guided the design and interpretation of the empirical research.

A mixed-methods approach between literature review and evaluation from the survey results was adopted to bridge the gap between theoretical frameworks and professional interest groups’ knowledge, offering an in-depth evaluation for VGS integration into historic buildings. The overall methodology of this study is encompassed and is demonstrated in Figure 2.

2.1. Survey Design

In the research, open-ended questions (Part A) were used to gather respondents’ initial, unbiased opinions about the benefits and challenges of VGS implementation on historic building facades. Subsequently, closed-ended questions (Part B) were employed to examine how these opinions varied after respondents were exposed to detailed, science-based information and specific examples drawn from the literature. The survey employs the umbrella term VGS to encompass both green façades and living wall systems. This decision was made to avoid overly prescriptive language and to allow respondents to draw on their own specialty and interpretive frameworks. The survey began with two open-ended questions designed to capture participants’ spontaneous perspectives without external influence:

(A1)

Do you think there are any benefits to growing VGS on historic building facades?

(A2)

Do you have any concerns about installing VGS on historic building facades?

After the open-ended questions, respondents were given multiple-choice (‘closed-ended’) questions. These questions included examples of the positive and negative impacts of VGS on historic buildings, derived from a literature review, grouped into environmental, social, economic, cultural, legal, and technical aspects. Respondents were permitted to choose more than one answer. These questions included:

(B1)

If you think VGS has any positive impact on historic building facades, please tick those that apply:

• ENVIRONMENTAL (e.g., reduces surface temperature, increases biodiversity)
• SOCIAL (e.g., improves health and well-being, provides recreational space)
• ECONOMIC (e.g., reduces energy costs, increases property values)
• CULTURAL (e.g., improves the aesthetics of the facade, enhances the city’s image)
• LEGAL (e.g., provides green certificates, supports community-led development)
• TECHNICAL (e.g., expands the lifespan of the building facade)
• No positive impacts

(B2)

If you think VGS has any negative impact on historic building facades, please tick those that apply:

• ENVIRONMENTAL (e.g., induces mold, attracts pests and mosquitoes)
• SOCIAL (e.g., triggers allergies)
• ECONOMIC (e.g., high installation and maintenance costs lead to unaffordable housing)
• CULTURAL (e.g., hides facade details, causes stains and dirt accumulation)
• LEGAL (e.g., lack of guidance, insufficient funding)
• TECHNICAL (e.g., roots damage the wall, difficult to install and maintain)
• No negative impacts

To gain demographic insights, the survey included profiling questions covering age, gender, education level, and country of residence. Additionally, the survey captured respondents’ levels of interest in VGS, historic buildings, or both fields, as well as information about their living environments, such as whether they lived in buildings with or without VGS and in historic buildings with or without VGS.

2.2. Survey Data Collection

The survey was administered online using Qualtrics. It targeted participants in the fields of environmental sciences, building conservation, and VGS-related disciplines. Considering the tension between conservation scientists and climate adaptation measures, the intent was to gather informed perspectives from individuals with disciplinary knowledge or practical experience relevant to the integration of VGS on historic buildings. To ensure the inclusion of relevant professionals, the survey was distributed through various professional networks, conferences, and organizations specializing in these fields.

Participants specialized in the built environment and historic building conservation were contacted through various channels. In Belgium, organizations such as the Flemish Heritage Agency (Onroerend Efgoed Vlaanderen), ICOMOS-BE, Monumentenwacht, and practitioners from the Belgian professional network for restoration architects GORDUNA were invited to participate. Additionally, attendees of the EGU General Assembly 2024 (European Geosciences Union) and DS²BE (Doctoral Seminars on Sustainability Research in the Built Environment) conferences, especially those presenting on topics related to cultural heritage, were also contacted.

As for the participants from the field of VGS, specific governmental bodies, such as the municipalities of Antwerp and Ghent, were contacted. Companies specializing in VGS design and implementation, including Groene Gevels, Blauw Groen Vlaanderen, and Gevelgroen, were also engaged. NGOs like Eco Huis, Burgerbegroting, and Plantwerpen contributed additional technical insights and case studies of existing projects. Furthermore, conference respondents from the EGU General Assembly 2024 and DS²BE who presented on nature-based solutions, such as VGS technologies and urban biodiversity, were contacted.

In total, responses were collected from 83 participants out of 165 individuals contacted. Based on their stated area of interest at the beginning of the survey, participants were grouped into three categories: those with a focus on historic building conservation, those with a focus on VGS, and those engaged in both fields. The heritage-focused group included researchers and practitioners working in cultural heritage and the built environment. The VGS-focused group comprised architects, landscape designers, and environmental scientists with experience in VGS. The group active in both fields consisted of individuals involved in projects that integrate VGS into historic buildings, combining perspectives from heritage conservation and sustainable design.

Sub-categorization was based on participants’ broader disciplinary backgrounds, including their roles in the built environment, nature-based solutions, and environmental sciences. Those categorized under the built environment group included architects, engineers, and researchers working in the building and construction sector, with familiarity in both heritage conservation and VGS. The nature-based solutions group consisted of individuals with applied knowledge of VGS and related ecological strategies within urban settings. The environmental sciences group comprised participants with academic or professional backgrounds in fundamental sciences such as geology, biology, chemistry, or material science, whose work intersects with building performance and environmental impact.

The survey was distributed both nationally and internationally. While most institutional participants were based in Belgium, the inclusion of conference attendees ensured representation from other European and non-European countries. This dual approach enriched the diversity of insights and experiences collected for the study on the integration of VGS onto historic buildings.

2.3. Respondent Profile

To conduct the study, 165 individuals were contacted, resulting in 83 valid responses. Among the respondents, there was a gender distribution of 55% women, 41% men, and 4% who preferred not to respond. The respondents’ age distribution was mainly concentrated in the 30–39-year-old age group (29%), followed by the 40–49-year-old age group (24%), the 18–29-year-old age group (19%), and equal representation in the 50–59- and 60–70-year-old age groups (14% each). The majority of respondents are from Belgium (41%) and other European countries (43%), followed by non-European countries (16%).

While the sample of 83 respondents cannot be considered statistically representative of all professionals working on environmental sciences, building conservation, or VGS-related disciplines, it offers a diverse and international cross-section of disciplinary viewpoints. The demographic breakdown indicates that the majority of respondents hold either a master’s degree (50%) or a PhD (41%), reflecting a highly educated group of participants. Their professional backgrounds are particularly relevant to this research, with 42% specializing in cultural heritage conservation, 16% in environmental sciences, 16% in nature-based solutions, and 13% in the built environment. Notably, 8% of respondents possess specific interest in VGS, although only 5% specialize in the integration of VGS on historic buildings.

57% of the respondents live in contemporary buildings without VGS. Respondents residing in buildings with VGS make up 18%, and those in historic buildings 22%; 3% of the respondents live in historic buildings with VGS.

2.4. Analysis of the Survey Data

The analysis of the survey data involved both qualitative and quantitative approaches, aimed at comprehensively understanding respondents’ views on the implementation of VGS on historic buildings.

2.4.1. Open-Ended Questions—Part A

The responses to the open-ended questions were analyzed using NVivo software. Each response was coded into one of seven aspects of sustainability: environmental, social, economic, cultural, legal, and technical, and an aspect for responses that indicated no perceived benefits or concerns (Appendix A). These aspects were derived from the existing literature to ensure consistency with established frameworks in the field. Following the coding process, thematic analysis was conducted to identify recurring themes within each aspect. This allowed for the identification of patterns in respondents’ perceptions of VGS on historic buildings. To facilitate a quantitative comparison, the qualitative data was subsequently transformed into numerical form by counting the frequency of responses within each aspect. This enabled statistical analysis and comparison across different aspects as well as with part B.

2.4.2. Closed-Ended Questions—Part B

Responses to the closed-ended, multiple-choice questions were analyzed using IBM SPSS Statistics 29.0.2.0 and Microsoft Excel. Descriptive statistical techniques were applied to calculate frequencies and percentages for each responded aspect. As respondents could select multiple options, a multiple-response analysis was conducted to identify the most frequently acknowledged benefits and concerns across the six sustainability aspects: environmental, social, economic, cultural, legal, and technical, as well as the “no benefit” or “no concern” aspect. The multiple choices for the closed-ended questions were derived from existing literature, allowing for a structured evaluation of respondents’ perceptions. The total number of selections for each aspect was counted, and descriptive statistics, including frequencies and percentages, were calculated to represent the prominence of each aspect in the closed-ended responses.

2.4.3. Consistency Rate Analysis of Part A and Part B

This section evaluates the alignment between respondents’ perceptions of the benefits and concerns associated with VGS based on their unprompted responses (Part A) and structured responses (Part B). The consistency rate analysis quantifies the degree of agreement between these two formats, providing insights into how respondents’ initial, spontaneous views align with their responses when presented with predefined examples and categories.

The consistency rate (CR) for each aspect (e.g., environmental, social, economic, cultural, legal, and technical) was calculated using the following formula (Formula (1)):

$$CR=\left({\displaystyle \frac{NumberofConsistentResponses}{TotalNumberofResponses}}\right)\times 10$$

(1)

where:

• Number of Consistent Responses is the count of cases where the binary-coded responses (1 = yes, 0 = no) from Part A and Part B matched.
• Total Number of Responses is the total number of respondents (corresponding to 83 respondents).

The analysis involved encoding all responses into binary values to standardize data across both open-ended and closed-ended formats. Consistency was determined at the individual level by comparing binary responses for each aspect. Consistent responses were then grouped by aspect and aggregated to calculate the percentage of consistent responses, enabling a clear comparison of consistency across different aspects.

Finally, statistical analysis was conducted on the calculated consistency rates to identify patterns and trends. This analysis revealed how structured prompts in Part B influenced respondents’ acknowledgment of benefits and concerns compared to their unprompted reflections in Part A, providing insights into the reliability and variability of responses between the two formats.

3. Results and Discussion

This section analyzes survey responses to explore professional interest groups’ perspectives on VGS in historic buildings, comparing open-ended (Part A) and closed-ended (Part B) responses across six aspects, highlighting benefits, concerns, and shifts in opinions.

3.1. Part A—Responses to Open-Ended Questions of the Survey

After responses were categorized, the perceived benefits and concerns of implementing VGS on historic buildings were evaluated. Overall, 89% of respondents recognized potential benefits, while 11% identified no advantages. Conversely, 85% expressed concerns, and 15% reported no significant issues, highlighting the dual opportunities and challenges of VGS integration.

To better understand these contrasting views, we examined the backgrounds of respondents at the extremes of the spectrum. Among those who perceived no benefits, the majority (6 participants) had a background in historic building preservation; those who reported no concerns were also predominantly affiliated with historic preservation (5 participants), with an additional 2 participants specializing in VGS applications on historic buildings. This suggests that even within the same professional domain, perceptions are not monolithic; rather, they may vary based on personal experience and familiarity with emerging technologies.

Environmental benefits were the most frequently cited, mentioned by 74% of respondents, including thermal comfort, improved air quality, enhanced biodiversity, and urban heat mitigation. Cultural benefits followed, noted by 47% of respondents, who emphasized VGS’s aesthetic value, such as visual appeal and compatibility with architectural styles. However, cultural concerns also emerged prominently, reflecting fears of obscuring architectural details and compromising material integrity. Technical benefits, mentioned by 29%, included facade protection from environmental stressors and extending the lifespan of buildings. Social and economic benefits were less frequently cited, mentioned by 13% and 6% of respondents, respectively, with social benefits focusing on public health and community engagement and economic benefits emphasizing energy cost savings. No respondents spontaneously identified legal benefits, indicating a gap in awareness of incentives like green certifications (Figure 3).

Technical concerns dominated negative responses, raised by 68% of participants, including structural risks like root penetration, material degradation, and maintenance challenges, underscoring the need for technical expertise. Cultural concerns followed, noted by 29%, with apprehensions about visual impacts and loss of architectural details. Other concerns (social, economic, environmental, and legal) were raised by only 4–5% of respondents, reflecting their secondary importance. Interestingly, 15% of respondents reported no concerns (Figure 3).

These findings emphasize cultural considerations as both a benefit and a concern, underscoring the need to balance aesthetic contributions with the preservation of material integrity, a key challenge in integrating sustainable solutions into heritage conservation.

3.1.1. Environmental Aspects

In evaluating the environmental aspects, this section considers both the perceived benefits, such as improved thermal comfort, enhanced air quality, and increased biodiversity, and the potential challenges of integrating VGS into historic buildings identified by professional interest groups, including pest attraction and the climatic adaptability of selected plant species (Table 1).

Environmental benefits were more prominently recognized than concerns. Respondents identified thermal comfort as the primary environmental benefit of VGS on historic buildings (Figure 4), citing its cooling effect during hot periods and thermal insulation during cold periods. This perception is consistent with existing scientific studies highlighting the thermal performance of VGS [22,23,24,25,26,27,28,29]. Air quality improvement was another frequently mentioned benefit, attributed to air purification, CO₂ reduction, and increased humidity. These insights closely align with the literature supporting VGS as tools for enhancing air quality [17,19,33,34,35,36,37]. Another benefit identified by respondents was the provision of green space and biodiversity enhancement, especially in dense urban areas. VGS were perceived as contributing to the creation of continuous green corridors, supporting urban ecology. These responses reflect findings in recent literature that underscore the role of VGS in promoting biodiversity [38,39,40]. Moderately recognized benefits included the mitigation of urban heat island effects and promotion of energy efficiency. Interestingly, while respondents rated these benefits as secondary, they are more prominently featured in the literature [23,48,49,50,51,52,53,54,55,56], suggesting a potential knowledge gap or lower public awareness regarding these impacts. Less frequently mentioned were the roles of VGS in reducing noise pollution and enhancing sustainability. While these were not considered primary motivators for adoption by respondents, literature has shown that VGS can reduce ambient noise by up to 3 dB [31]. This discrepancy points to a lack of awareness among users or stakeholders about such subtler benefits.

Despite the generally positive outlook, respondents raised valid environmental concerns. The main environmental concerns reported were the attraction of pests and mosquitoes and the increased risk of bio-colonization, both of which may cause material degradation and increase maintenance needs. These concerns are echoed in scholarly discussions on the biological interactions between vegetation and building materials [76]. Less commonly expressed concerns included climatic compatibility and plant health, particularly regarding the challenges in selecting suitable plant species for local conditions and ensuring their long-term viability (Figure 4). Notably, the scientific literature also seldom addresses these topics in depth, indicating a shared gap in research and awareness.

3.1.2. Social Aspects

In evaluating the social aspects, this section considers perceived benefits, such as enhanced well-being, inclusivity, and community engagement, and concerns raised by professional interest groups, including potential issues related to urban equity, quality of life, and green gentrification when integrating VGS into historic buildings (Table 1).

Respondents identified promoting public health as the primary social benefit of VGS on historic buildings (Figure 4). Mental health improvements and protection for vulnerable groups, such as those in schools and hospitals, were emphasized. Enhanced well-being was also highlighted, as VGS can create a happier and more vibrant atmosphere by increasing green space and improving aesthetics. These perspectives are well-supported in the literature, where similar benefits related to mental and physical health are consistently highlighted [64,65,66,67]. Additionally, respondents noted that VGS can foster community engagement by sparking conversations and encouraging involvement in their maintenance and implementation. This aligns with findings in the literature that describe VGS as part of a co-design approach involving local governments, private sectors, and citizens to foster a sense of ownership and shared responsibility, thereby increasing the success rate of such initiatives [73,74]. Although mentioned less frequently, several respondents also saw VGS as a pedagogical resource, particularly for raising environmental and biological awareness. This mirrors academic findings suggesting that VGS can contribute to supportive learning environments, both in terms of academic outcomes and personal development, by making abstract environmental concepts tangible and accessible [19,34].

The most critical social concern raised was the risk of green gentrification. Respondents expressed concerns that VGS might lead to higher property values, displacement of lower-income residents, and changes in community dynamics. Notably, this concern is represented only in a few studies in the literature [84,85], indicating a potential research gap that requires further investigation. Other concerns included reduced quality of life, possibly due to pests, mosquitoes, or reduced light, though these were seen as secondary. Health risks, such as allergies or mold, were mentioned but considered the least significant drawback. These issues are also well-documented in the literature as social barriers to the integration of VGS in the built environment [80].

3.1.3. Economic Aspects

In evaluating the economic aspects, this section examines the perceived benefits of VGS on historic buildings in terms of energy cost reduction, façade protection, and potential job creation, as well as concerns related to high installation and maintenance costs, as expressed by professional interest groups (Table 1).

Respondents identified energy cost reduction as the most significant economic benefit of VGS on historic buildings, emphasizing energy efficiency and savings on heating and cooling (Figure 4). This aligns with findings in the literature, where energy savings are among the most frequently cited economic advantages of VGS [34,68,69]. Other perceived economic benefits included the protection of building façades, which can lead to extended material lifespan and reduced maintenance costs over time. Although mentioned less frequently, some respondents also acknowledged the potential for job creation related to the installation and ongoing care of VGS. These aspects, however, are rarely addressed in the existing literature, indicating an area in need of further exploration and empirical evidence.

The primary economic concern was the high initial installation cost, seen as a major barrier to adoption. Maintenance costs, including watering, pruning, and repairs, were also noted as moderate concerns. These economic barriers are well-documented in the literature and remain consistent across various studies [16,18,19,21,33,37,81,82,83].

3.1.4. Cultural Aspects

In evaluating the cultural aspects, this section explores how professional interest groups perceive the impact of introducing VGS on historic buildings on aesthetic, symbolic, and heritage significance (Table 1). Cultural considerations include the potential to enhance visual appeal and promote green cultural values, alongside concerns about compromising authenticity, obscuring architectural details, and disrupting the historic character of façades.

Respondents identified the primary cultural benefit of VGS on historic buildings as aesthetic improvement (Figure 4). VGS attracts attention through seasonal variations, colors, and the ability to complement architectural styles. It also improves the street silhouette, hides wall imperfections, and creates a vibrant ambiance, making cities more pleasant and visually appealing. Some respondents noted that VGS promotes green culture and provides new conservation methods by integrating nature into historic urban environments, though this was less emphasized.

The primary cultural concern is the potential for VGS to obscure or alter façade details, raising fears of compromising intricate and historically significant architectural features (Figure 4). Respondents expressed concerns about damaging cultural value, threatening the material integrity of buildings, and causing irreversible changes to historic buildings. Additional issues include the lack of contextual harmony, incompatibility with building materials, and the risk of creating a neglected appearance. To address these concerns, respondents emphasized the need for thorough analysis of the building and its local context prior to VGS implementation, ensuring that the aesthetic contributions of VGS do not compromise the authenticity or the integrity of the building.

These concerns align with established restoration principles, which emphasize the importance of maintaining the authenticity, spirit of place, and visual coherence of historic buildings through new interventions [4,5,6]. While the literature does recognize the aesthetic value of VGS in contemporary architecture [15,18,33,34,57,58,59,60], it often adopts a more cautious stance when such interventions pose a risk of obscuring historically significant features, diminishing aesthetic clarity, or introducing material vulnerabilities [7,79].

The results illustrate the tension between innovation and conservation by highlighting both the cultural opportunities that well-designed VGS can unlock and the serious concerns about its potential to compromise visual and material integrity. Interestingly, respondents tended to emphasize the positive aesthetic potential of VGS, reflecting a more optimistic view than is commonly seen in conservation discussions, where concerns about material integrity and authenticity usually take place.

3.1.5. Legal Aspects

This section highlights the legal constraints identified by professional interest groups regarding the implementation of VGS on historic buildings (Table 1). Unlike other aspects, no perceived legal benefits were reported in this domain.

The main legal issue regarding VGS on historic buildings seems to be the difficulty of implementing it in listed buildings, as represented in Figure 4. Respondents pointed out that getting permission and complying with the strict regulations governing alterations to protected or listed buildings is perceived as a significant problem. Ensuring regulatory compliance with VGS practices is also mentioned as one of the concerns; responses suggest that this relies on the flexibility of building codes and laws protecting heritage sites. These concerns are echoed in the literature, which points to complex regulatory systems, inconsistent standards, and administrative or political challenges as major legal barriers to the adoption of VGS in heritage contexts [21,37,86,87].

3.1.6. Technical Aspects

This section presents professional interest groups’ views on the technical implications of applying VGS to historic buildings. Drawing on the evaluation framework outlined in Table 1, the analysis considers both the potential benefits, such as the capacity of VGS to shield façades from environmental stressors, and the concerns raised regarding material compatibility, structural durability, and long-term maintenance requirements.

Respondents identified the primary technical benefit of VGS on historic buildings as protection from environmental effects (Figure 4). VGS are valued for shielding buildings from weather, pollution, and UV radiation, while also providing shade to regulate temperature. Some respondents noted additional benefits, such as protection against impurities, biocolonization, and corrosion, as well as the use of vegetation as a historic conservation method. These benefits are also addressed in the literature, where the VGS can shelter the building facades from the UV radiation and acid rain [32,69,70,75].

However, technical concerns remain. The main technical concern is the potential reduction in facade longevity, with respondents highlighting risks such as material alteration, facade degradation, and root penetration, which may harm material integrity. Maintenance challenges and conservation issues are also significant barriers, particularly the need for ongoing care to prevent problems like uncontrolled plant growth. Increased humidity was another notable concern, as it may lead to mold formation and negatively affect building materials and indoor environments. Respondents also expressed worries about impurities, irrigation damage, and potential stains or cracks caused by VGS. Less frequently mentioned concerns included disruptions to rainwater drainage, which could exacerbate other issues. These technical challenges are well-documented in the literature, particularly regarding material compatibility, system maintenance, and long-term performance risks [15,16,21,33,37,94]. Overall, the responses reflect a growing awareness among practitioners of both the protective functions and the technical limitations of VGS in heritage contexts.

3.2. Part B—Responses to Closed-Ended Questions of the Survey

The closed-ended multiple-choice survey differed from the open-ended format by providing respondents with predefined examples of benefits or concerns. This allowed respondents to select multiple options that they considered applicable.

The results revealed clear trends in perceptions. A majority of respondents (87%) recognized the environmental benefits of VGS, such as reducing surface temperatures and enhancing biodiversity. Cultural benefits were acknowledged by 74%, with respondents highlighting improvements in aesthetics and the city’s image. Similarly, 74% recognized social benefits, such as enhancing health and well-being and providing recreational space. Economic benefits were identified by 54% of respondents, citing reduced energy costs and increased property values. Technical benefits, including extended façade lifespan, were noted by 28%, while legal benefits, such as supporting green certifications, were recognized by 23%. Only 7% of respondents indicated that VGS has no positive impact (Figure 5).

Regarding concerns, technical issues were the most frequently mentioned, cited by 80% of respondents. Key concerns included damage to walls, installation challenges, and maintenance difficulties. Cultural concerns, raised by 59%, included VGS obscuring significant façade details and causing staining, potentially compromising the authenticity of historic buildings. Economic concerns, highlighted by 29% of respondents, focused on high installation and maintenance costs, reflecting the dual nature of VGS’s economic implications: long-term financial benefits versus substantial upfront investment. Environmental concerns, cited by 36%, included mold growth, pest attraction, and the use of non-biodegradable materials (e.g., PVC, EPDM membranes, and synthetic geotextiles, which are the components of drainage layers, root barriers, and irrigation channels of living wall systems). Legal concerns, noted by 23%, centered on unclear guidelines and insufficient funding for VGS projects, creating uncertainty for implementation. Social concerns were less prominent, mentioned by 13%, with risks such as allergies or health issues. Interestingly, 8% of respondents perceived no significant negative impacts of VGS (Figure 5).

3.3. Comparison Between Responses of Part A and Part B

The analysis of responses from Part A (open-ended questions) and Part B (closed-ended questions) reveals notable differences in how professional interest groups perceive the benefits and concerns of implementing VGS on historic buildings, underscoring the role of structured prompts in capturing broader perspectives.

Environmental benefits were consistently recognized across formats, cited by 74% in Part A and 87% in Part B, with a high consistency rate of 84% (Figure 6,

Table 2. Consistency Rates for Perceived Benefits of VGS Implementation on Historic Buildings: Comparison Between Open-Ended (Part A) and Closed-Ended (Part B) Survey Responses.

Aspects	Consistency Rate Between Part A and Part B
Environmental	84
Social	36
Economic	52
Cultural	66
Legal	77
Technical	80
No Benefits	94

). This highlights the strong association between VGS and environmental advantages, reflecting their perceived importance in promoting urban sustainability.

Other aspects, such as social and economic benefits, showed greater discrepancies. Social benefits were mentioned by only 13% of respondents in Part A but rose to 74% in Part B, resulting in a low consistency rate of 36%. Similarly, economic benefits increased from 6% in Part A to 54% in Part B, with a consistency rate of 52%. These findings suggest that these aspects are less intuitively associated with VGS without explicit prompts.

Cultural benefits demonstrated moderate alignment, with acknowledgment increasing from 47% in Part A to 74% in Part B (consistency rate: 66%). Legal benefits, absent in open-ended responses, were recognized by 23% in Part B, highlighting the importance of structured questions in uncovering underrepresented perspectives.

The consistency rates for concerns varied across aspects, reflecting the perception of professional interest groups. Technical concerns emerged as the most prominent and consistently recognized issue, with 68% of respondents identifying them in Part A and 80% in Part B, resulting in a consistency rate of 69% (Figure 6,

Table 3. Consistency Rates for Perceived Concern of VGS Implementation on Historic Buildings: Comparison Between Open-Ended (Part A) and Closed-Ended (Part B) Survey Responses.

Aspects	Consistency Rate Between Part A and Part B
Environmental	67
Social	84
Economic	72
Cultural	55
Legal	78
Technical	69
No Concerns	83

). This highlights a widespread acknowledgment of the material and maintenance challenges posed by VGS.

Environmental concerns demonstrated a moderate consistency rate of 67%, with acknowledgment rising from 4% in Part A to 36% in Part B. This indicates that while environmental benefits are more readily recognized spontaneously, explicit prompts significantly enhance awareness of associated risks, such as pest attraction and mold growth.

Cultural concerns showed a lower consistency rate of 55%, with acknowledgment increasing from 29% in Part A to 59% in Part B (Figure 6, Table 3). This suggests that although cultural concerns, such as risks to architectural details, are noted in open-ended responses, they become more prominent when explicitly prompted.

Similarly, economic concerns were underreported in Part A (4%) but rose to 29% in Part B, yielding a consistency rate of 72% (Figure 6, Table 3). This suggests that respondents do not initially prioritize economic concerns but recognize them when provided with specific examples, such as high installation and maintenance costs.

Social concerns and the “no concerns” category exhibited the highest consistency rates, at 84% and 83%, respectively. Social concerns were cited by 5% of respondents in Part A and 13% in Part B (Figure 6, Table 3), indicating that respondents generally perceive social risks, such as green gentrification or health issues, as less significant compared to other aspects.

The comparison between open-ended and closed-ended responses reveals four key findings. First, environmental benefits and technical concerns emerged as the most immediate associations, reflecting a strong parallel view among professional interest groups regarding their significance in VGS applications. Environmental benefits, such as reducing surface temperatures, improving air quality, and enhancing biodiversity, position VGS as an effective tool for urban sustainability, a finding supported by studies highlighting its environmental advantages [23,34,38]. In contrast, technical concerns remain a significant barrier, with participants emphasizing risks such as root penetration that may compromise material integrity, material degradation, and the increased maintenance demands associated with VGS [15,16,21,33,94].

Second, the higher acknowledgment of social, economic, and legal factors in closed-ended responses further indicates that these aspects, though not spontaneously mentioned, are recognized when explicitly prompted. This suggests that participants acknowledged VGS’s potential to improve health and well-being [64,65,66], reduce energy cost [69], and encourage green initiatives [37,72] when presented with specific examples, all of which are well-documented in the literature. On the other hand, concerns such as VGS’s potential to trigger allergies [80], high installation cost [16,18,19,21,33,37,81,82], and the challenges posed by complex regulations and lack of standards [21,37,86,87] were only recognized when explicitly prompted.

Third, cultural considerations take a unique position as both a significant benefit and a prominent concern. Participants widely recognize the aesthetic value of VGS, viewing it as a tool for enhancing the visual appeal of historic buildings. However, there are notable apprehensions about its potential to obscure intricate architectural details or harm the material integrity of the building. This dual perspective aligns with the literature, which highlights VGS’s historical role in improving urban aesthetics [63], while cautioning against risks to the authenticity of historic facades [7]. These findings emphasize the importance of achieving a balanced design approach that enhances aesthetics without compromising cultural heritage. Meanwhile, addressing technical challenges such as material integrity and maintenance demands remains essential for the successful integration of VGS on historic buildings.

Finally, the comparison between open-ended and closed-ended responses highlights the significant influence of question format on participants’ opinions. While open-ended responses reflect participants’ immediate associations, primarily focusing on environmental benefits and technical concerns, the closed-ended responses revealed a broader recognition of social, economic, and legal factors. This disparity suggests that these aspects, though less intuitive, are acknowledged when explicitly prompted, pointing to a potential gap in awareness or prioritization of VGS’s multifaceted impacts on heritage buildings. This finding highlights the need for targeted communication strategies and structured frameworks that emphasize underrecognized benefits, such as economic and social opportunities. For example, policymakers and practitioners could promote VGS not only as an environmental solution but also as a tool for enhancing public well-being, reducing long-term energy costs, and aligning with regulatory incentives.

4. Conclusions

This study provides a professional interest-group-based evaluation of VGS on historic buildings, analyzed through a six-aspect framework: environmental, social, economic, cultural, legal, and technical. A key contribution of this research lies in its mixed-methods approach, which integrates a systematic literature review with survey data from 83 professionals. This methodology captured both unprompted views (open-ended responses) and the broader range of concerns and opportunities (closed-ended responses), which highlighted the gaps between perception and awareness.

This study addressed two central research questions: (1) How do professional interest groups perceive the benefits and concerns associated with implementing VGS on historic buildings? and (2) To what extent are these perceptions consistent across different modes of evaluation?

In response to the first question, the survey findings highlight that environmental benefits are the most widely acknowledged. These appeared in 74% of open-ended and 87% of closed-ended responses, with an 84% consistency rate. Participants emphasized the aesthetic contributions of VGS, with 68% mentioning this in their open-ended responses and 80% indicating it in the closed-ended responses. This indicates a growing acceptance of nature-based aesthetics, particularly when VGS are designed to complement rather than obscure historical character. However, technical concerns, particularly related to material compatibility and long-term maintenance, remain significant barriers to implementation. Additionally, one striking pattern is noticeable: the majority of participants expressed both benefits and concerns, while only a minority took extreme positions (i.e., saw no benefits or no concerns). This suggests that professionals largely acknowledge the complexity of integrating VGS into historical contexts; however, their views may vary depending on their disciplinary background.

Regarding the second question, the comparison of open- and closed-ended responses reveals that response format significantly influences perception. While open-ended answers reflected immediate associations, largely focused on environmental and technical themes, closed-ended responses prompted broader recognition of social, economic, and legal considerations. This finding suggests that when explicitly prompted, professionals tend to adopt a more holistic view, highlighting the importance of structured engagement in future policy and planning dialogues.

A comparison between the survey data and existing literature adds further insight. Both sources prominently featured environmental and technical aspects, indicating a consistent focus in these areas. However, participants highlighted cultural, social, economic, and legal factors in their responses more than what was noted in the scholarly research. This difference suggests that there is a need for addressing both of these challenges and opportunities by improving technical guidance, analyzing the existing research more effectively, and building interdisciplinary literacy for more informed, balanced decision-making in future projects.

Both the survey and literature also stress the critical challenge of achieving cultural and technical compatibility between VGS and historic buildings. Addressing this challenge requires context-sensitive, reversible, and non-invasive design approaches that do not obscure or damage significant architectural features. Tools like Heritage Impact Assessments can help decision-makers balance environmental goals with heritage conservation values [100].

This study is not without limitations. First, it relies on self-reported data, which may reflect individual biases or variations in disciplinary expertise. Although the survey targeted interest groups in either heritage conservation or VGS, only a small proportion of participants demonstrated integrated expertise in both fields. This disciplinary asymmetry may influence how certain benefits or concerns are prioritized. Additionally, the sample is geographically concentrated, with a significant number of respondents based in a single regional context. As a result, perceptions may reflect sector-specific priorities rather than balanced interdisciplinary insight. Finally, the study is based on a perception-driven methodology, which captures professional attitudes and expectations but does not evaluate the actual physical or environmental performance of VGS interventions. As such, these insights should be understood as representing professional interest groups’ opinions rather than empirical outcomes. Addressing this limitation through future research that incorporates comparative regional or project-based case studies would enhance the depth and generalizability of the findings.

To build on these insights, future research should incorporate a broader and more diverse respondent sample, employing complementary methods such as interviews or focus groups to explore perceptions in greater depth. Although the study partially examines how professional backgrounds influence opinions, future research should explore this aspect more deeply. Long-term and design-based studies are also needed to evaluate the ongoing benefits and concerns of VGS, particularly their impact on historic buildings. By addressing these gaps and developing interdisciplinary approaches, VGS can be positioned as a viable solution that bridges the goals of urban sustainability and cultural heritage preservation.