A Bibliometric Review of the Development and Challenges of Vernacular Architecture within the Urbanisation Context

Abstract

An effective strategy for sustainable development is to conduct research on vernacular architecture in response to urbanisation as well as environmental and climate change challenges. However, focused discussion has been limited to date due to the diverse range of disciplines involved in vernacular architecture and the unique examples in practice. Scopus, one of the largest literature databases, was used to find and select a total of 1403 documents for this paper. Techniques for both quantitative and qualitative literature analysis were employed using Microsoft Excel (Version 16.75.2) and the visualisation tool VOSviewer (Version 1.6.19). Using bibliometric analysis, more academic publications were reviewed, aiming to analyse the current situation, influence, and future direction of the literature related to vernacular architecture. The current issues have been obtained from the statistical results, and the opportunities and challenges of vernacular architecture in today’s cities are discussed. The twenty most frequently referenced publications, keywords, and correlations between co-occurrences were all examined in this bibliometric analysis, along with annual publishing trends and the most influential nations, institutions, sources, and authors. The analysis showed a rising trend in vernacular architectural publications, with China, Italy, and Spain being the most prolific nations whose institutions have a high academic impact. However, the degree of international author collaboration remains insignificant. Future themes could focus on energy, comfort, earthquake resilience, and sustainability, with cultural heritage and vernacular communities still receiving little research attention. This study is a comprehensive bibliometric analysis of vernacular architecture, as well as an important study of sustainability and resilience, affirming the importance of vernacular architecture in terms of future urban form and drawing on the lessons of history. Also, the proposed research framework could be a strong reference for future researchers looking for inspiration.

1. Introduction

With increasing urbanization, population growth, and rising living standards, sustainability—regarding energy use, buildings, and the environment—is becoming more widely discussed [1]. In an era of tremendous changes in the scale of society and technology, sustainability can help restore important local resources as well as preserve traditional identities [2]. Furthermore, the main purpose of sustainability is to harness the environmental potential to provide comfort to residents [3,4]. However, environmental issues are not specific to individual countries, and finding sustainable solutions for existing buildings remains challenging in terms of energy efficiency [5,6]. The previous literature reveals that academics agree that vernacular architecture, as a product of adaptation to local conditions, connects the past and is a testimony of cultural identity. Through the use of vernacular materials and available resources, sustainability for the environment can be achieved [7]. Thus, vernacular architecture may represent a means of addressing the challenges of urban development. Research confirms that vernacular architecture is an important architectural heritage [8,9], the result of human behaviour, and the best example of harmonious coexistence between architecture and the natural environment. It reflects people’s traditions, culture, needs, and future expectations [10]. According to studies, vernacular architecture is unique to each region of the world and is substantially influenced by the local climate [11]. Each style may be individual, but the key element is the architecture and the life scenes that take place within it [12]. Vernacular architecture reflects the unique cultural and landscape elements of the area and represents a locally adapted approach to building materials [13]. Understandably, it is the outcome of historical optimisation as a structure that uses readily available materials and well-known construction methods to offer comfort in the local climate [14]. The study of vernacular architecture is not only the intellectual domain of architecture; it also covers sociology, economics, the environment, and cultural studies, which evolve sequentially over time. However, dramatic socio-political events around the world can also have an impact on the development of vernacular architecture [15]. Thus, there is a growing awareness that the life history of vernacular architecture can tell the story of a city’s rapid development and the enormous changes that affect the social and urban fabric [16]. The study of vernacular architecture is therefore a significant research topic.

The desire to modernise has led to a massive urban renaissance, including “megacities” [16]. Experts continue to debate the complex and successful blending of urbanisation trends and vernacular architecture [17]. Given the current challenges of global warming, climate change, and energy reduction, some scholars have started to conduct research on maintaining indoor thermal environments [18] as well as topics related to building energy consumption [19]. Studies have shown that the retrofitting of modern cooling solutions (e.g., electric air conditioning units) constitutes the most common form of retrofitting of traditional houses by a considerable margin [16]. Researchers generally agree that most modern buildings require high energy consumption to maintain indoor temperatures, while vernacular architecture, characterised by accumulated experience, is well adapted to the climate, environment, and social culture [18,20]. Therefore, vernacular building space is a key element in regulating the thermal environment of buildings and the thermal adaptation of residents [21]. Although many scholars have explored the perspective of indoor comfort, few studies have applied these results. In addition, some urban policymakers ignore existing problems and opt to demolish vernacular architectures or replicate and rebuild them, making it difficult to ensure sustainable urban development and collaborative governance [22,23]. Furthermore, this also severs the continuity between architectural history and urban life and blurs the connections between them, a contradiction leading to identity crisis in many contemporary cities. Urban renewal in different urban and rural spaces has also weakened heritage properties and increased the energy burden of buildings [24]. Therefore, the study of local climate and traditional construction materials can facilitate their integration or transformation using modern technologies and values; this can lead to proposals for new models of sustainable development [1,10,25]. Due to the inherent vulnerability of vernacular architecture, there is also a research gap to be filled in terms of seismic risk assessment and building conservation [26,27]. In recent years, it has been shown that in the era of high-performance architecture, a combination of traditional materials and modern technologies should be sought in order to fulfil the technical potential of buildings [28]. Countries such as Palestine and China have many vernacular courtyard construction techniques. These not only harmonise with the climatic environment but are also supported by strong religious and spiritual beliefs [4,29]. Some scholars have adopted a qualitative interpretive approach to the solution of vernacular architecture [3], but few studies have yet focused on the cultural and heritage narratives embedded behind the architecture. Traditional regional culture and historical memory are slowly disappearing, and there is great scope for the resilience of vernacular architecture and cultural landscapes in the current context of climate change [13]. Based on the present challenges, architectural practitioners and researchers still need to reflect on this shift towards culture and heritage [30]. Nevertheless, many historical experiences have yet to be grasped and applied to modern architecture. Vernacular heritage is important because of its connection to local culture; for instance, the use and shaping of space, traditional techniques, and material practices [9]. To date, research collaboration projects in various countries, among institutions of all kinds, have been infrequent, and it remains understudied. It is therefore necessary to carefully review the past, analyse the current situation, and conceptualise the future. In fact, the study of vernacular architecture is constantly changing with the discovery of technology, and the research hotspots and keywords are constantly updated by technology and discovery. The fragility of vernacular architecture renders it vulnerable to disappearance [31,32], so it is important to take a holistic view and select the most recent and largest database for bibliometric analysis. Thus, this study adopted a bibliometric-based review of the literature to discuss the significance of vernacular architecture in contemporary cities and environments and to draw lessons from it, thereby contributing to architectural resilience and sustainability. Therefore, the research questions in this study are as follows:

• RQ1: What are the publication trends in the field of vernacular architecture, and what are the implications for the future of architecture?
• RQ2: Which are the most influential countries, institutions, and authors that discuss the way in which vernacular architecture relates to cities?
• RQ3: Which are the most cited publications, and do they address the experiences and lessons learned in vernacular architecture?
• RQ4: What are the key themes that emerge from the co-occurrence analysis in the vernacular architecture literature, and how do they contribute to architectural resilience and urban sustainability?

To address these research questions, the sections of the paper are detailed as follows. Section 2 contains the research methodology, which explains the research methods, phases, and specific procedures used in this study. The results of the study are presented in Section 3, including the annual publication trends on vernacular architecture, the status of the literature published, citation relationships, keywords, and co-occurrence network analysis. The issues raised in the research questions concerning the relationship between vernacular architecture and urban development are also provided. This is followed by Section 4, the discussion of the findings, which responds to the research questions by dissecting the theoretical, methodological, and practical aspects of the contribution, affirming the importance of vernacular architecture in the future of humankind, as well as the construction experiences and lessons learned. Furthermore, reflections on the limitations that exist in this study are shown, and recommendations for future research are made. Section 5 summarises this bibliometric review on vernacular architecture.

2. Materials and Methods

The aim of this study is to investigate and assess the current state, impact, and future potential of vernacular architecture research on a global scale. In this study, the current research dynamics and field of vernacular architecture are brought together. To pinpoint significant contributions and predict future research directions and innovations, data indicators in the body of the existing literature are evaluated. Therefore, this study contains a quantitative-based and qualitative literature review methodology. This approach combines rigorous data analysis with a deeper understanding of the phenomenon [33]. For instance, bibliometric analysis can help shed light on the overall landscape and impact of vernacular architecture research by clarifying the connections between authors, publications, institutions, and other features of the research field, which can map and broaden the knowledge of the research field [34]. Qualitative aids can provide additional insight that reaches beyond quantitative analysis, resulting in a deeper understanding of the theories, cultural concepts, historical developments, and perspectives behind vernacular architecture. Thus, the interpretation of bias and subjective judgments can be addressed through a mixed-methods systematic evaluation [35], enhancing the depth and breadth of understanding [36].

The Scopus database was chosen for this bibliometric study, as it is considered the most extensive interdisciplinary content and citation database [37,38]. Containing publications from scientific publishers around the world, it is now used globally for many large-scale analyses [39]. Thus, this study can provide a comprehensive understanding of the results of scientific research on vernacular architecture around the world. Figure 1 presents the overall research methodology as well as the operational framework of this section.

2.1. Bibliometric Search

In terms of search strategy, it is necessary to use the proper keywords when conducting bibliometric searches. In this case, a description of the research topic was the first step of “vernacular architecture”, establishing the research aim based on the research question, then conducting a search in the Scopus database. The authors then used the following search keywords in combination with Boolean operations (quotation marks, OR *, and EID):

TITLE (“Vernacular architecture” OR “Traditional architecture” OR “Folk architecture” OR “Indigenous architecture” OR “Local architecture” OR “Rural architecture” OR “Ethnic architecture” OR “Native architecture” OR “Regional architecture” OR “Architectural tradition*” OR “Traditional building method*” OR “Vernacular construction technique*” OR “Vernacular building” OR “Traditional building” OR “Indigenous building” OR “Local building” OR “Rural building” OR “Regional building”).

This study focuses on the article title, which attracts the attention of practitioners and scholars in the field of study, enables a substantive assessment [40,41], and most visually reflects the relevance of the study, making the final bibliometric analysis results more accurate. Furthermore, the time frame was determined as the 21st century onwards, namely from 2000 to June 2023. By extending the time frame to 2023, the timeliness and novelty of this study can be increased, providing insight into the latest research developments. A better understanding of new theories, methods, and trends helps this study to reveal emerging topics and research directions. The final number of documents retrieved was 1539.

2.2. Science Cleaning and Processing

The existing data needed to be cleaned and processed after the basic search data were located. As shown in Figure 1, this bibliometric analysis required a complete documentation record, so the document types were limited to articles, conference papers, book chapters, reviews, and books, which was the initial cleanup (n = 1509). In addition, Scopus allows the direct reading of paper abstracts, so irrelevant documents were removed by browsing (n = 20). Moreover, trade journals were further excluded (n = 6). It is important to highlight that, after browsing all the documents, some double meanings of the search terms remained. For example, “local architecture” means “the architecture of localities” in vernacular architecture, but there are also expressions such as “automation of local architecture processes for digital transformation”. In addition, the term “regional architecture” in vernacular architecture refers to “architecture in a particular regional culture”, but there are also articles that discuss “national strategic relationships in a networked regional architecture”. In response, the titles and abstracts were carefully read to ensure that the data were solid and relevant, and irrelevant documents were excluded to finalise the data cleaning and processing (n = 1403). Stage 2 of Figure 1 shows this process.

2.3. Quantitative Analysis of Data

Bibliometric methods in knowledge mapping allow for examining the relationships between disciplines, fields, specialties, and individual papers [42]. This is also an essential element in providing researchers with the means to identify avenues and new directions related to the subject of scientific research [34]. For this reason, this study used bibliometric analysis to identify areas of knowledge, research trends, and directions in vernacular architecture, among others. Therefore, the choice of software for the collaborative processing of quantitative data is equally important. The quantitative analysis of relevant literature, using VOSviewer, allows the creation of knowledge maps. Visual analysis of vernacular architecture is included, as are the latest advances and frontier hotspots of research [43]. The free software produces aggressive results in the case of medium and large data sets and is an excellent choice for scientific cartographic analysis [44].

In terms of data manipulation, Figure 1 provides an overview of the Scopus data exported in Stages 1 and 2. Opened as an Excel file, each exported entry includes all the necessary details about each publication, such as the title, author, affiliation, and keywords. It is worth noting that there is incomplete information in the exported Scopus data, which needs to be supplemented to make the data solid and harmonious. The Scopus advanced search interface enables the manual supplementation of author affiliation information based on EID. Afterwards, using Open Refine software (Version 3.7.2), clean data were exported and uploaded to VOSviewer for visualisation and discussion of the annual publication trends and the most prolific authors, institutions, and countries; this also reveals co-occurrence networks based on titles and abstracts in the field of vernacular architecture. Thus, in the first part of Stage 3, VOSviewer was used for the bibliometric analysis. This lays the foundation for the qualitative analysis that follows.

2.4. Qualitative Analysis of Literature

To address the limitations of the bibliometric analysis, qualitative methods were also employed, thereby creating a more comprehensive and accurate picture of scholarly communication beyond academic publications [45]. In this stage, the top 20 cited documents were selected for detailed analysis. Highly cited publications have been shown to make significant contributions in terms of research areas, themes, and trends [46]. Therefore, qualitative integration in the bibliometric analysis is a deep dive into the quantitative results to explore necessary clues and potential future research directions for the field of vernacular architecture. Thus, the body of knowledge and the evolutionary process of the subject matter can be more scientifically identified and discussed [47]. In addition, this can help to better answer RQ3.

Finally, there is a discussion on the data analysis. Based on the bibliometric analysis conducted in the previous steps as well as the qualitative analysis of the literature, the main contributions of the aforementioned publications were summarised in terms of their theoretical, methodological, and practical aspects. In addition, the limitations of current vernacular architecture research were critically discussed, helping to provide comprehensiveness, transparency, and credibility to this study. Consequently, appropriate recommendations are offered for future research, and other researchers are encouraged to expand and enrich the research in the field of vernacular architecture, filling the remaining knowledge gaps.

3. Results

Using the study’s analysable data as the foundation for the bibliometric analysis, the results were derived from the data and ultimately used to address the research questions. Specifically, this section discusses the overview of the bibliometric analysis study of vernacular architecture, wherein 1403 documents were retrieved and screened from the Scopus database, including publications from 2000 to June 2023. The bibliometric analysis is a quantitative assessment of the number of publications and presents them visually [48,49]. This study used VOSviewer processing and tabular statistics to present and compare key information about publications, annual publication trends, and the most productive and significant authors, as well as the institutions of affiliation, countries, and a map of their relationships.

3.1. Overview of the Documents

Following a preliminary analysis of the document types in the retrieved data,

Table 1. The basic information for bibliometric analyses, as document, source, and language types. (Notes: TPs = total publications).

No.	Document Type (Top 4)	TPs	%	No.	Source Type	TPs	%	No.	Language Category (Top 8)	TPs	%
1	Article	724	51.49	1	Journal	764	54.34	1	English	1272	90.47
2	Conference Paper	459	32.65	2	Conference Proceeding	369	26.24	2	Chinese	64	4.55
3	Book Chapter	163	11.59	3	Book	162	11.52	3	Spanish	30	2.13
4	Review	46	3.27	4	Book Series	111	7.89	4	Portuguese	10	0.71

shows that in the field of vernacular architecture, most of the results were published in the form of articles (n = 724), accounting for 51.49% of the total document types. Conference papers on vernacular architecture were also prominent (n = 459), comprising 32.65% of the total documents. Academic conferences can facilitate networking, the exchange of the latest results, collaboration, and advocacy, which translate into more effective research programs and initiatives in the academic field [50]. Some scholars have also discussed vernacular architecture in book chapters (n = 163).

In addition, this study determined the types of documents in which vernacular architecture subjects were published by analysing the bibliometric data based on the type of document source. According to Table 1, journals were the most common source, accounting for 54.34% of the total (n = 369), followed by conference proceedings (n = 369), which comprised 26.24%. The rest were books (n = 162) and book series (n = 111), accounting for 11.52% and 7.89%, respectively. A cross-sectional comparison of document types and sources reveals that journal articles, conference proceedings, and book chapters have similar proportions in their respective classifications, thus allowing for a basic determination of the relative accuracy of the data in this bibliometric study. Of these published documents, English was the dominant language of publication (n = 1272), accounting for 90.47% of the total language types. Since this study explores the current state, impact, and expectations of the global vernacular architecture field, language types were not excluded. In addition to English, the other prominent languages are Chinese (4.55%), Spanish (2.13%), and Portuguese (0.71%). The top eight language types are listed on the right side of Table 1; the proportion of publications in other languages is far lower.

3.2. Publishing Trends and Building Futures

Following the analysis of basic documentation information, the focus of this section is on the evolution and growth of publication trends in the research published in vernacular architecture since 2000. This includes important information such as TPs, NCPs, TCs, C/P, and h-index.

Table 2. Annual publication information from 2000 to 2030 (Notes: NCPs = number of cited publications; TCs = total citations; C/P = average citations per publication; h = h-index).

Year	TPs	NCPs	TCs	C/P	h	Year	TPs	NCPs	TCs	C/P	h
2000	2	1	2	1.00	1	2012	63	32	359	5.70	9
2001	10	3	9	0.90	2	2013	92	55	600	6.52	11
2002	10	6	23	2.30	3	2014	102	58	659	6.46	10
2003	9	5	59	6.56	4	2015	98	57	565	5.77	11
2004	8	5	156	19.50	5	2016	89	61	496	5.57	11
2005	25	20	247	9.88	8	2017	83	54	892	10.75	15
2006	33	25	227	6.88	8	2018	107	74	495	4.63	11
2007	22	16	536	24.36	9	2019	94	62	521	5.54	13
2008	16	9	55	3.44	5	2020	137	84	316	2.31	9
2009	28	19	261	9.32	6	2021	110	59	279	2.54	9
2010	40	29	591	14.78	12	2022	115	43	182	1.58	7
2011	67	45	598	8.93	10	2023	43	6	7	0.16	1

presents the annual publication statistics of vernacular architecture research from 2000 to June 2023, visually indicating the increasing trend of publications. In 2000, only two publications on vernacular architecture were published and indexed in Scopus. In one, Thomas [51] suggests that the form and nature of traditional architectural styles may be considered a force in the complex world of contemporary architectural design. Cennamo et al. [52] also provided a forward-looking discussion on the issue of the relationship between artificial and natural intelligence in rural architecture, which opened a new era in the emergence of regional architecture in the twenty-first century. The literature started to increase in 2001. Interestingly, the TCs on vernacular architecture increased dramatically in 2007, with 22 publications and 536 TCs in that year. The highest TCs in the decade was in 2011 (n = 598). From 2012 onwards, there has been an overall trend of increased scholarly output as well as citations in the field of vernacular architecture, reflecting the growing interest in the subject. However, the quantity of publications declined slightly in 2017 (n = 83), although the number of TCs in that year (n = 892) was the highest in the field since 2000.

The evolution of architecture and related disciplines follows a similar trend. Figure 2 provides a visualisation of the trend of TPs and TCs, indicating three distinct phases. The first phase is the positive contribution. This phase was relatively slow in number and pace, and laid the groundwork as research began to focus on climate impacts, folk environment and culture, vernacular matrices, and environmental synergy [53,54,55]. The book “Vernacular Architecture in the 21st Century: Theory, Education and Practice” [56] was published in 2005, focusing on the purpose and significance of vernacular architecture in the twenty-first century. Research has shown that a systematic study of history, vernacular technologies, and categories is needed to truly understand the past and present living conditions of these buildings [57]. The year 2007 was representative, with several papers noted and cited by scholars. Within the field of architecture, interdisciplinary research in the areas of physics, agronomy, urban planning, and engineering science blossomed. In particular, contributions were made to the direction of traditional building structures and conservation, and sustainable development [58,59,60,61]. In this bibliometric study, it is appropriate to look at the research trends in the field, which are visible from the data of the first phase. Subsequently, at the beginning of the second phase, several representative articles were published that discuss the use of solar passive technologies in vernacular buildings [62] and the energy performance and evaluation of ancient vernacular architecture [63]. The third phase is also growing steadily. According to Figure 2, there were 270 TPs in the first seven years, 2000–2007, comprising 19% (about one-fifth) of the TPs. The following decade, 2007–2017, saw a total of 527 publications, an increase that effectively responds to the question about research trends. After that, until June 2023, it is possible to forecast that the number of publications will increase based on the analysis of the data.

3.3. Status of Literature Publication

3.3.1. National Contributions

Due to the accessibility of bibliometric data and other advantages [64], co-authorship is representative of research collaboration. Critical for linking scholars’ research findings to the outside world, co-authorship can also provide opportunities for the in-depth analysis of knowledge networks [65]. To find and evaluate partnerships in the field of vernacular architecture, specific locations and relationships in the connectivity network were determined based on the analysis of data from co-authors. Thus, this study was able to respond to the publication trends mentioned in RQ1. The asymptotic quantitative characteristics and the influence of collaboration on publications were similarly enhanced [66]. Therefore, the results of the co-authorship analysis also explain the second research question (RQ2) of this study: “Which are the most influential countries, institutions, and authors that discuss the way in which vernacular architecture relates to cities?” Microsoft Excel and VOSviewer were used to analyse the bibliometric data, from countries to institutions, to journals, and finally to authors and individuals, in a macro-specific order.

Firstly, the top 20 most prolific nations were ranked using the search data, as shown in

Table 3. The top 20 countries with the highest research output and activity (Notes: g = g − index; PYS = Publication Year Start).

Rank 1	Country	TPs	TCs	NCPs	C/P	h	g	Citable Year	PYS
1	China	311	1051	155	3.38	17	17	23	2001
2	Italy	121	1074	88	8.88	16	9	24	2000
3	Spain	105	578	65	5.50	12	9	20	2004
4	United States	91	976	54	10.73	14	8	23	2001
5	United Kingdom	79	636	55	8.05	15	7	24	2000
6	Turkey	65	287	39	4.42	10	7	19	2005
7	Indonesia	65	125	40	1.92	5	7	11	2013
8	India	59	761	39	12.90	12	6	18	2006
9	Portugal	54	414	33	7.67	13	6	17	2007
10	Iran	46	238	29	5.17	8	6	19	2005
11	Japan	35	252	18	7.20	5	5	22	2002
12	Australia	26	97	18	3.73	6	4	19	2005
13	South Korea	23	130	13	5.65	6	4	22	2002
14	Cyprus	19	209	14	11.00	8	2	14	2010
15	Romania	19	58	7	3.05	4	4	14	2010
16	Germany	18	324	12	18.00	4	3	17	2007
17	Greece	18	212	14	11.78	5	3	19	2005
18	France	18	64	8	3.56	3	3	21	2003
19	Nigeria	16	75	11	4.69	5	3	15	2009
20	Russian	16	37	11	2.31	4	3	13	2011

¹ Ranking based on total publications.

. The table covers TPs, TCs, NCPs, C/P, h-index, g-index, PYS, and so on. China has led the TPs on vernacular architectural subjects from 2001 until 2023 (n = 311). This is followed by Italy (n = 121), Spain (n = 105), and the United States (n = 91). In addition, China, Italy, the United Kingdom, Japan, South Korea, and France published their research earlier (during 2000–2003), while Indonesia, Cyprus, Romania, and Russia started later (during 2013–2011) but published more results in recent years. In terms of TCs, the literature from China (n = 1051), Italy (n = 1074), the United States (n = 976), India (n = 761), and the UK (n = 636) has a certain academic impact. These are the overall interpretations of the tabular data and the response to RQ2, and VOSviewer contributes to data visualisation.

As shown in the exported map of Figure 3—which represents a network of national co-authorship based on years cited more than four times—the number of countries meeting this threshold is 56. According to the figure, the yellow portion denotes latecomers, and the purple portion denotes countries with earlier publications. It is evident that the United States, Greece, Israel, Norway, and Austria published the first studies on vernacular architecture, with the United Kingdom and South Korea following. This is followed by China, Italy, India, and Spain, which have more co-authorship networks. Latecomers are represented by the warmest colours in Figure 3, such as Hungary, Iraq, and Indonesia, where publications in the field of vernacular architecture appeared only gradually around 2021. Interestingly, the countries in the middle of Figure 3 cooperate closely, while the countries on the periphery lack direct inter-country co-authorship with each other.

3.3.2. Institutional Production and Networks

After analysing the co-authorship relationships among countries, institutions within countries were selected as the unit of analysis, containing sections such as TPs, TCs, and PYS to identify the most productive institutions that conduct research on vernacular architecture. The earliest years of publication for the most prolific institutions are after 2002, with four institutions in China, three in Portugal, and the rest in Iran, Spain, and the United Kingdom. Notably, two of the most prolific institutions in

Table 4. Top 10 most productive institutions.

Rank 1	Institution	Country of Location	TPs	TCs	PYS
1	Xi’an University of Architecture and Technology	China	78	228	2002
2	Escola Superior Gallaecia	Portugal	26	202	2015
3	Xi’an University of Technology	China	22	59	2019
4	Tongji University	China	20	143	2006
5	University of Minho	Portugal	19	307	2014
6	Islamic Azad University	Iran	18	79	2009
7	Universidad Politécnica de Madrid	Spain	15	124	2004
8	Zhejiang University	China	14	6	2012
9	Polytechnic Institute of Leiria	Portugal	13	234	2015
10	Oxford Brookes University	United Kingdom	13	164	2005

¹ Ranking based on total publications.

are in Xi’an, China: the Xi’an University of Architecture and Technology (n = 78) and the Xi’an University of Technology (n = 22). Since Xi’an is the ancient capital of thirteen dynasties in Chinese history, there are a large number of vernacular architectural styles and remains. Consequently, the area has been the focus of relatively many research cases, such as the effect on human thermal comfort in the arid climate zone of Xi’an [21], the regeneration of vernacular architecture in northwest China [67], and the ecological study of energy-efficient indoor thermal environments in rural buildings [68]. However, the two universities differ in that the year of research at Xi’an University of Architecture and Technology predates Xi’an University of Technology by seventeen years, and therefore there is a significant difference in the TCs (n = 228; n = 59). In addition, although the University of Minho in Portugal has published 19 papers since 2014, it has a TC count of 307. These studies include, for instance, the harmonisation of Mediterranean vernacular architecture with its local environment, culture, and tradition, environmental and climatic factors, vernacular materials and sustainability, thermal performance, and comfort conditions, among other subdivisions [4,28,69]. Furthermore, the Universidad Politécnica de Madrid in Spain can be considered one of the pioneers in publishing academic publications, according to the publication date and number of citations at the institution. In general, only individual institutions specialise in the field of vernacular architecture, and the number of published documents remains insufficient.

Following the identification of the ten institutions with the highest productivity, the next step was the analysis of the literature sources. The use of bibliometric indexing allows for a better understanding of the impact of publications and helps researchers keep track of submission trends. Thus, scholars are better able to select the most appropriate journals for submission [70].

Table 5. The most cited journals with more than 50 citations as well as their respective CiteScore, SJR, SNIP, and quartile.

Journal Title	TCs	TPs	PYS	Publisher	CiteScore 2022	SJR 2022	SNIP 2022	Quartile
Renewable and Sustainable Energy Reviews	282	3	2016	Elsevier	26.3	3.232	3.631	Q1
Sustainability (Switzerland)	268	32	2016	MDPI	5.8	0.664	1.198	Q1
Journal of Civil Engineering and Management	123	3	2003	Vilnius Gediminas Technical University	5.9	0.653	1.399	Q1
Energy	102	4	2017	Elsevier	14.9	1.989	2.132	Q1
Sustainable Cities and Society	102	7	2011	Elsevier	18.4	2.305	2.509	Q1
Solar Energy	75	3	2011	Elsevier	13.1	1.373	1.708	Q1
Energies	66	7	2018	MDPI	5.5	0.632	1.025	Q1
Energy Policy	65	1	2014	Elsevier	15.2	2.292	2.155	Q1
Applied Energy	60	1	2014	Elsevier	21.1	2.907	2.758	Q1
Renewable Energy	50	3	2000	Elsevier	16.1	1.815	2.146	Q1

shows the results of the analysis of the source publications used in this study. This includes the SCImago Journal Rank 2022 (SJR) and the Normalized Source of Impact per Paper (SNIP). According to the Scopus database statement and industry consensus, the SJR is the weighted number of citations received by the source title and is intended to measure the prestige of the journal. The SNIP compensates for differences in citation potential and is intended to account for differences in subjectivity across research areas [71]. Thus, this section analyses the journals in terms of TCs, TPs, PYS, and publisher, and discloses the 10 publications in the field of vernacular architecture that have been cited more than 50 times. In addition, these are compared and counted with the latest 2022 CiteScore, SJR, SNIP, and quartile, and their potential in terms of research contribution and journal development in vernacular architecture is discussed.

The top 10 journals were finally identified. The most cited journal (n = 282), as shown in Table 5, is Renewable and Sustainable Energy Reviews, affiliated with the Elsevier publisher. Three papers have been highly cited since 2016, with Webb’s [72] contribution, which has now received 197 citations, reviewing the criteria, analytical methods, and decision-making processes for evaluating historical and conventional building energy retrofits. Furthermore, it suggests the effectiveness of energy retrofits in conventional buildings, while also providing a valuable reference for future related research. Following closely with 71 citations, Chandel et al.’s [58] study discusses the ways in which vernacular materials and architectural features can be used to enhance thermal comfort in contemporary structures in a number of different countries around the world, thus adapting to modern architecture and current lifestyles. In addition, studies in vernacular architecture conservation have found that many countries still do not have clear national standards and guidelines [73]. As Table 5 reveals, in 2014, two articles published in the Energy Policy and Applied Energy journals had a high number of citations. Among them, the article published in Energy Policy has 65 TCs. The authors are from China; their work is related to China’s proposal to “promote the construction of a new socialist countryside” and the government’s call for energy saving and emission reduction in rural buildings in order to narrow the energy gap between regions [74]. Another review article, similar to the abovementioned one on indoor thermal comfort, uses the indigenous inhabitants of a specific area as a case study. It was found that the residents did not want to change their environment [75], which also validates the need for vernacular architecture conservation to some extent. Overall, the bibliometric statistics in Table 5 reveal that, among the current publishers, Elsevier is more prominent in the discussion on vernacular architecture. In addition, the top 10 cited journals are all rated Q1 in the latest Scopus journal rankings for 2022.

3.3.3. Production Sources and Levels

Figure 4 presents the citations of article sources, setting the minimum number of citations for a source at six. Of a total of 396 sources, 40 meet this threshold, in addition to 20 journals with connected relationships. Thus, the highly cited journals in Table 5, including Renewable and Sustainable Energy Reviews, Solar Energy, Energy Policy, Applied Energy, and Renewable Energy, meet the threshold but lack source connections and therefore do not appear in Figure 4. It can be observed from the figure that Building and Environment in the field of vernacular architecture was published earlier and had a wide impact. Many of the journals that appeared afterwards had “vernacular” as the source title; for instance, Vernacular and Earthen Architecture: Conservation and Sustainability, Vernacular Architecture, Vernacular Architecture in the 21st Century: Theory, Education and Practice, Vernacular Architecture in the Pre-Columbian Americas, Vernacular Architecture: Towards a Sustainable Future, Vernacular Heritage, and Earthen Architecture. For scholars in this field, searching for keywords is a relatively efficient way to select relevant journals and submit appropriate manuscripts. In addition, the yellow dots represent journals that have published more papers on the topic of vernacular architecture with citation amounts. Energies, Sustainability (Switzerland), and Buildings have been searched in Scopus since 2008, 2009, and 2011, respectively, and are among the journals that have grown rapidly in recent years. At the same time, the International Journal of Architectural Heritage and the Frontiers of Architectural Research are publishing more articles about vernacular architectural heritage. It is important to note that the ISVS e-journal has existed since 2015 and still has room to grow. Its purpose is to study and debate vernacular architecture and society as well as to help organise academic conferences. In short, this analysis measures the influence of each journal in the field of research on vernacular architecture by counting the number of times a document has been cited by other papers.

3.3.4. Authors’ Scientific Productivity

The previous section analysed the most influential literature sources. In this section, the most influential authors, as well as the co-authorship and co-citation of article authors, will be discussed. First, the co-authorship analysis was conducted using Microsoft Excel for the Scopus data, as depicted in Figure 5. The orange proxy refers to the statistics of a single author in the literature and the black represents the statistics of the presence of multiple authors. The comparison shows that, since 2007, the number of co-authored publications has exceeded that of solo-authored works, with this contrast increasing each year. Co-authorship emphasises the evolving pattern of scientific collaboration, especially among researchers in specific research areas as well as interdisciplinary research [76]. It is also evident from Figure 5 that among the published results in vernacular architecture from the year 2000 to date, the number of independent author publications peaked in 2014 (n = 39) and began to decline thereafter, reflecting the trend of authorship collaboration in interdisciplinary research.

Among the 1403 documents, some authors have published results on vernacular architecture that have a significant number of citations. Therefore, the top 15 most influential authors are ranked according to the TCs, as shown in

Table 6. Top 15 most cited authors in the field of vernacular architecture.

Rank 1	Author’s Name	TCs	TPs	NCPs	C/P	PYS
1	Singh, M.K.	360	8	8	45	2009
2	Mahapatra, S.	360	8	8	45	2009
3	Atreya, S.K.	358	6	6	59.66	2009
4	Rodrigues, H.	234	13	12	18	2015
5	Webb, A.L.	197	1	1	197	2017
6	Correia, M.	193	17	11	11.35	2015
7	Vasconcelos, G.	182	10	9	18.2	2015
8	Ortega, J.	175	8	7	21.87	2015
9	Zavadskas, E.K.	169	1	1	169	2007
10	Antucheviciene, J.	169	1	1	169	2007
11	Philokyprou, M.	167	13	10	12.84	2011
12	Michael, A.	157	9	8	17.44	2014
13	Zhai, Z.	153	1	1	153	2010
14	Previtali, J.M.	153	2	1	76.5	2010
15	Yang, X.	145	5	4	29	2013

¹ Ranking based on total citations.

. It also covers the information for TPs, NCPs, C/P, and PYS. As depicted in Table 6, Singh M.K., Mahapatra S., and Atreya S.K. have published 6–8 papers each since 2009, with TCs of approximately 360. The reason for their similar results is that they are co-authors on several articles. Most previous bibliometric analyses have used only the first author’s co-citation count as evidence that the author made a contribution [77]. In this paper, on the other hand, the statistics are not based on the order of authors but on the complete list of publications. Similarly, Webb A.L. [72] has 197 citations in one article, which is one of the latest published in Table 6. Zavadskas E.K. and Antucheviciene J., with 169 citations in one article, propose a regenerative solution for vernacular architecture [78]. Zhai Z. and Previtali J.M. have also made significant contributions to the field of vernacular architecture, with one article and 153 citations [63]. The next most numerous publications are by Correia M. (n = 17), followed by Rodrigues H. (n = 13) and Philokyprou M. (n = 13).

In addition, an analysis of authors’ co-citations was performed. In VOSviewer, the unit of analysis is selected as “cited authors”, and the minimum number of citations per author is selected as 35. There are 67 authors who meet the threshold, and the final visualisation of co-citation is shown in Figure 6. The evolution of the ratio from single authors to multiple authors, the most influential authors, and the visualisation of co-citations among authors are shown. It can be said that participation and collaboration can positively impact the expansion and integration of future research in the field of architecture, generating greater possibilities for development.

Based on an analysis of the current publication landscape, the second research question (RQ2) is answered: “Which are the most influential countries, institutions, and authors that discuss the way in which vernacular architecture relates to cities?” Next, the third research question (RQ3) will be interpreted: “Which are the most cited publications, and do they address the experiences and lessons learned in vernacular architecture?”

3.4. Highly Cited Documents

The data for this bibliometric analysis were not screened for country and language, with the aim of exploring the results of the global vernacular architecture literature and identifying the most influential literature. In addition, key citations in the citation analysis contribute to the construction of knowledge [79]. The number of citations for an article indicates its interest and importance in the field of study. This can also explain RQ3, the most cited publication, as shown in Table 7. In this study, the top 20 articles with more than 60 citations were identified by ranking each article according to its TCs, from highest to lowest.

The most cited article is Energy Retrofits in Historic and Traditional Buildings: A Review of Problems and Methods by Webb A.L. [72], with a total of 197 citations. The article assesses the need for energy renovation to balance multiple criteria, including energy consumption, building fabric, occupant demand, collections, economics, energy use, and climate change. It argues that energy renovation not only reduces energy consumption but also preserves historic and traditional buildings for future generations. The second-ranked article is Multiple Criteria Evaluation of Rural Building’s Regeneration Alternatives by Zavadskas E.K. and Antucheviciene J. [78], with 169 citations. Regeneration options for abandoned buildings in rural areas of Lithuania are discussed and prioritised for areas at different levels of development, providing a case study for future studies in other areas. Following this are two articles with 153 citations each. One of the studies, titled Thermal Performance Study and Evaluation of Comfort Temperatures in Vernacular Buildings of North-East India [62], used the vernacular buildings of North-East India as a case study, finding that these folk houses performed satisfactorily and the occupants were comfortable in a wider range of temperatures except in winter. This has largely inspired scholars, and thermal comfort has become a popular area of research. Another study, Ancient Vernacular Architecture: Characteristics Categorization and Energy Performance Evaluation by Zhai Z. and Previtali J.M. [63], presents a methodology for categorising different folk areas and evaluating the energy performance of ancient folk houses, using folk building techniques to determine the best way to build them. It enriches the knowledge base on vernacular architecture and suggests that the cultural aspects of vernacular architecture also deserve attention.

Vernacular architectures covered in other articles include climate regulation and adaptive strategies for urban and vernacular architecture [14,32,58,80,81,82], building energy [74,75,83,84], regional spatial planning [61,85], vernacular architecture and airflow analysis [86], and building structure and seismic research [27,31,87]. By analysing the highly cited documents, it is possible for potential researchers to fully understand the research dynamics and future challenges of vernacular architecture and to take the opportunity to identify research gaps therein, improve the current situation, and thus make a sustained contribution to vernacular architecture.

Table 7. Top 20 highly cited documents based on total citations.

Rank 1	Source	Title	TCs
1	[72]	Energy Retrofits in Historic and Traditional Buildings: A Review of Problems and Methods	197
2	[78]	Multiple Criteria Evaluation of Rural Building’s Regeneration Alternatives	169
3	[62]	Thermal Performance Study and Evaluation of Comfort Temperatures in Vernacular Buildings of North-East India	153
4	[63]	Ancient Vernacular Architecture: Characteristics Categorization and Energy Performance Evaluation	153
5	[81]	How High Albedo and Traditional Buildings’ Materials and Vegetation Affect the Quality of Urban Microclimate. A Case Study	140
6	[80]	Bioclimatism and Vernacular Architecture of North-East India	114
7	[14]	Climate Responsive Building Design Strategies of Vernacular Architecture in Nepal	110
8	[61]	Estimation of Regional Building-Related C&D Debris Generation and Composition: Case Study for Florida, US	110
9	[83]	Energy and Environment in Chinese Rural Buildings: Situations, Challenges, and Intervention Strategies	100
10	[84]	Thermographic Survey of Two Rural Buildings in Spain	83
11	[85]	A Site Planning Approach for Rural Buildings into A Landscape Using A Spatial Multi-Criteria Decision Analysis Methodology	80
12	[82]	Energy and Microclimatic Performance of Mediterranean Vernacular Buildings: The Sassi District of Matera and the Trulli District of Alberobello	78
13	[86]	Analysis Of Airflow Through Experimental Rural Buildings: Sensitivity to Turbulence Models	73
14	[31]	Force and Displacement Based Vulnerability Assessment for Traditional Buildings	73
15	[27]	Traditional Earthquake Resistant Techniques for Vernacular Architecture and Local Seismic Cultures: A Literature Review	73
16	[32]	Vernacular Architecture: Questions of Comfort and Practicability	72
17	[58]	Review of Energy Efficient Features in Vernacular Architecture for Improving Indoor Thermal Comfort Conditions	71
18	[87]	Architectural Structure and Environmental Performance of the Traditional Buildings in Florina, NW Greece	70
19	[74]	Overview of Rural Building Energy Efficiency in China	65
20	[75]	Thermal Comfort and Energy Consumption in Modern Versus Traditional Buildings in Cameroon: A Questionnaire-Based Statistical Study	60

¹ Ranking based on total citations.

Table 7. Top 20 highly cited documents based on total citations.

Rank 1	Source	Title	TCs
1	[72]	Energy Retrofits in Historic and Traditional Buildings: A Review of Problems and Methods	197
2	[78]	Multiple Criteria Evaluation of Rural Building’s Regeneration Alternatives	169
3	[62]	Thermal Performance Study and Evaluation of Comfort Temperatures in Vernacular Buildings of North-East India	153
4	[63]	Ancient Vernacular Architecture: Characteristics Categorization and Energy Performance Evaluation	153
5	[81]	How High Albedo and Traditional Buildings’ Materials and Vegetation Affect the Quality of Urban Microclimate. A Case Study	140
6	[80]	Bioclimatism and Vernacular Architecture of North-East India	114
7	[14]	Climate Responsive Building Design Strategies of Vernacular Architecture in Nepal	110
8	[61]	Estimation of Regional Building-Related C&D Debris Generation and Composition: Case Study for Florida, US	110
9	[83]	Energy and Environment in Chinese Rural Buildings: Situations, Challenges, and Intervention Strategies	100
10	[84]	Thermographic Survey of Two Rural Buildings in Spain	83
11	[85]	A Site Planning Approach for Rural Buildings into A Landscape Using A Spatial Multi-Criteria Decision Analysis Methodology	80
12	[82]	Energy and Microclimatic Performance of Mediterranean Vernacular Buildings: The Sassi District of Matera and the Trulli District of Alberobello	78
13	[86]	Analysis Of Airflow Through Experimental Rural Buildings: Sensitivity to Turbulence Models	73
14	[31]	Force and Displacement Based Vulnerability Assessment for Traditional Buildings	73
15	[27]	Traditional Earthquake Resistant Techniques for Vernacular Architecture and Local Seismic Cultures: A Literature Review	73
16	[32]	Vernacular Architecture: Questions of Comfort and Practicability	72
17	[58]	Review of Energy Efficient Features in Vernacular Architecture for Improving Indoor Thermal Comfort Conditions	71
18	[87]	Architectural Structure and Environmental Performance of the Traditional Buildings in Florina, NW Greece	70
19	[74]	Overview of Rural Building Energy Efficiency in China	65
20	[75]	Thermal Comfort and Energy Consumption in Modern Versus Traditional Buildings in Cameroon: A Questionnaire-Based Statistical Study	60

¹ Ranking based on total citations.

3.5. Co-Occurrence of Keywords

In bibliometric analysis, co-occurrence represents the use of metrics of relevance and information to quantitatively describe co-occurrence relationships. In the previous section, the most influential countries, institutions, sources, and authors were discussed. However, the themes and concepts of the literature expressed by keywords have not yet been mentioned. A co-occurrence analysis of keywords can better illustrate the focus, research areas, the development of key themes, and so on, within the research. Thus, the fourth research question (RQ4) can be answered: “What are the key themes that emerge from the co-occurrence analysis in the vernacular architecture literature, and how does this contribute to architectural resilience and urban sustainability?” Using VOSviewer, based on titles and abstract fields, all keywords were used as the focus of the analysis, in which at least 14 terms appear. The keyword co-occurrence is presented as a network visualisation graph in Figure 7. VOSviewer identifies keywords from the titles and abstracts of publications and categorises them with different colours of clusters. In Figure 7, there are four clusters: red, green, blue, and yellow. The size of each one represents the heaviness of the item’s appearance, while the density of the connection lines represents the strength of the connection between items. The same colour proxy refers to the related keyword appearances. For instance, the keywords “indoor environment”, “ventilation”, “thermal comfort”, “energy conservation”, and “climatology” are closely related to the terms indicated in red and appear simultaneously. The same is true for other colours.

Notably, as already mentioned in the methodology section, data quality issues arise due to the variability in data types and formats, data sources, and acquisitions [88], for which the process of cleaning and harmonising data requires great care. Therefore, a profiling analysis was performed using the open source tool OpenRefine [89], which led to a merging of similar keywords for author keywords and retrieved keywords. This avoids the duplication of keywords due to singular and plural, tense, lexical, and phrase combinations, making the results of the calculation more accurate and precise.

In these four clusters, the keywords “architecture”, “vernacular architecture”, “architectural design”, and “buildings” appear most frequently. Although the visual co-occurrence relationship map can visually present the distribution and relationship of each cluster, specific keywords still need to be listed in specific tables, so

Table A1. Keywords in vernacular architecture research, total link strength, and occurrences.

Keywords	Cluster	Weight Links Value	Total Link Strength	Occurrences	Theme
Architectural Design	1	77	472	108	Theme 1: Energy and Thermal Comfort
Housing	1	66	292	64
Energy Utilisation	1	54	266	48
Energy Efficiency	1	56	260	58
Energy Conservation	1	55	230	44
Surveys	1	60	205	43
Thermal Comfort	1	51	197	47
Walls (Structural Partitions)	1	57	190	34
Ventilation	1	51	184	36
Roofs	1	52	166	33
Heating	1	41	156	28
Climatology	1	42	124	24
Natural Ventilation	1	41	113	22
Residential Building	1	40	97	20
Thermal Insulation	1	39	96	22
Solar Energy	1	34	95	18
Thermal Performance	1	43	92	19
Indoor Air Temperature	1	32	86	16
Intelligent Buildings	1	41	82	15
Indoor Environment	1	29	76	15
Structural Design	1	41	74	17
Brick	1	35	72	18
Indoor Thermal Environments	1	34	72	15
Air Conditioning	1	31	69	14
Computer Software	1	30	68	14
Buildings	2	80	726	188	Theme 2: National Countermeasures and Seismology
Rural Areas	2	75	559	136
Rural Buildings	2	68	368	104
Earthquakes	2	36	213	49
Seismology	2	40	166	38
China	2	51	164	42
Earthquake Engineering	2	36	138	27
Structural Analysis	2	40	107	23
Eurasia	2	41	104	17
Retrofitting	2	42	103	22
Seismic Response	2	28	99	18
Masonry Materials	2	33	96	17
Timber	2	36	92	20
Earthquake Resistant	2	29	85	17
Asia	2	33	80	14
Seismic Design	2	25	80	15
Decision Making	2	41	79	18
Construction	2	36	78	21
Geophysics	2	27	73	16
Computer Simulation	2	37	72	17
Traditional Knowledge	2	22	51	16
Vernacular Architecture	3	82	1010	372	Theme 3: Vernacular Architectural Heritage Conservation and Sustainability
Sustainable Development	3	68	605	153
Historic Preservation	3	65	291	66
Vernacular Buildings	3	52	199	45
Sustainability	3	51	183	57
Cultural Heritages	3	49	182	39
Historic Building	3	48	104	24
Planning	3	35	99	23
Built Environment	3	35	79	17
Vernacular Building	3	34	71	22
Conservation	3	26	66	24
Climate Change	3	34	64	15
Construction Industry	3	29	56	15
Tourism	3	29	55	14
Italy	3	20	50	15
Construction Material	3	24	44	14
Heritage	3	26	44	15
Architecture	4	80	1030	308	Theme 4: Urban and Vernacular Architecture
Traditional Buildings	4	75	500	143
Traditional Architecture	4	73	469	179
Building Materials	4	60	244	75
Ecology	4	43	104	24
Construction Technique	4	36	91	19
Regional Planning	4	26	81	19
Restoration	4	29	67	18
Architectural Heritage	4	27	65	16
Modern Architectures	4	32	63	15
Urban Planning	4	33	60	14

is necessary (see Appendix A for details). It allows us to see the weight links value, total link strength, and occurrences of each keyword in each cluster. To facilitate a better overview of the content, each of the four clusters is named by topic. As can be seen in Table A1, “Energy Utilisation”, “Energy Efficiency”, “Energy Conservation”, “Thermal Comfort”, “Climatology”, “Thermal Insulation”, “Solar Energy”, “Indoor Air Temperature”, and other terms appear in Cluster 1, so it is named “Energy and Thermal Comfort”. These keywords indicate the importance and future prospects of research in the direction of energy consumption, climate, and occupant comfort in the field of vernacular architecture research [6,19,20,90,91,92,93,94]. Cluster 2 is named “National Countermeasures and Seismology”. It covers “Rural Areas”, “Eurasia”, “China”, “Earthquakes”, “Seismology”, “Earthquake Engineering”, “Seismic Response”, “Computer Simulation”, “Traditional Knowledge”, and other keywords relating to the protection of vernacular buildings in earthquakes in various countries. Countermeasures and materials are explored in each country [26,95,96]. The issue of the demolition or preservation of vernacular buildings has been debated as time and urbanisation change [32,97]. The third theme, “Vernacular Architectural Heritage Conservation and Sustainability”, is related to this group of keywords, including “Sustainable Development”, “Historic Preservation”, “Cultural Heritages”, “Historic Building”, “Conservation”, “Construction Industry”, “Tourism”, “Construction Material”, and so on. Most of these keywords appeared widely in publications only after 2015 [5,7,91,98,99,100,101,102]. The conservation and sustainable development of vernacular architecture have received the attention of the industry and scholars. Meanwhile, under the fourth theme of “Urban and Vernacular Architecture”, vernacular architecture is discussed from a relatively broad regional perspective, with keywords such as “Restoration”, “Regional Planning”, “Construction Technique”, “Modern Architectures”, “Urban Planning”, and “Rural Architecture”, etc. [20,90,97].

Through Figure 7 and Table A1, the co-occurrence analysis of keywords in the four themes allowed us to analyse the relationships between the terms. It is possible to move from “urban development” to “national responses and practices” to “heritage conservation” to “architectural comfort”, in the evolution of the word. These findings link the development process of vernacular architecture to the focus of attention at each stage. These findings not only respond to RQ4, but also validate the scholars’ exploration of the economic, cultural, policy, and social elements of vernacular architecture, thus providing logical and practical reference content for future studies.

4. Discussion

In terms of bibliometric analysis on the topic of vernacular architecture, this study has achieved the most up-to-date and comprehensive analysis. Not only does it analyse the data from the literature but, more importantly, it answers the research questions from the literature to better discuss the urban form as well as the future sustainability of vernacular architecture. Specifically, in terms of research methodology, the largest Scopus database was used to ensure search coverage and comply with a scientific and systematic process of data selection and screening, as shown in Figure 1. The data are presented in more detail in terms of metrics, such as TCs, h-index, and other breakdowns, resulting in different research insights. Moreover, the time frame covers the beginning of the 21st century to June 2023, with over two decades’ worth of data to better illuminate current and future research trends. In addition, this study is predicated on an examination of global vernacular architecture, so there is no exclusion of content in terms of language publication, which better ensures the integrity of the data. Furthermore, this bibliometric analysis provides a more systematic approach to the results of the study, which is useful from a theoretical, methodological, and practical standpoint. The article also serves as an integration and expansion of vernacular architecture research, enabling the discovery of more research gaps in the field of vernacular architecture and making a positive contribution to existing knowledge. Furthermore, by addressing the four research questions in the previous sections, it discusses and summarises them in terms of contributions and further presents the limitations, challenges, recommendations, and opportunities for future research related to the field of vernacular architecture.

4.1. Publishing Trends and Implications for the Future of Architecture

RQ1, “What are the publication trends in the field of vernacular architecture and is it possible to discover their implications for the future of architecture?”, is explained in Section 3.2. As can be seen in Table 2 and Figure 2, the overall research on vernacular architecture, as recorded in the Scopus database, shows an upward trend and an increasing interest in the subject. This trend has been rising significantly since 2001 and reached its highest output in 2020.

Trends in the literature indicate that China is one of the most active and influential countries in the field of vernacular architecture, with the highest TPs (n = 311) and 1051 TCs. The emphasis on preserving China’s vernacular heritage has been reflected through a series of policies, such as the development of the “Beautiful Countryside Program” since 2005 [9] and the implementation of the “Rural Revitalisation Strategy”, which is also related to the decline and preservation of vernacular architecture [103]. Moreover, China has a long cultural history, with its cultural values being carried by the architecture of the traditional vernacular. These have been discussed by many scholars [104], prompting the publication of relevant research results. Undeniably, China’s architectural heritage is vast, yet the consumption of vernacular heritage in commercialised “reconstruction” has generated new narratives related to the Chinese countryside. This has been demonstrated by studies of vernacular materials and features [25]. Therefore, the establishment of a genealogy of traditional vernacular architecture is conducive to the preservation of this heritage. Thus, it is crucial for the future development of architecture [104].

At the same time, Italy stands out with a total of 121 publications and 1074 citations. Like China, Italy also has a diverse and wide range of architectural styles and continues to advance on the research path of vernacular architecture. Figure 3 shows that the United States, Greece, Israel, Norway, and Austria have earlier publications on vernacular architecture.

Similarly, institutions within these countries are influential, such as Xi’an University of Architecture and Technology in China, with a total of 78 publications, and Escola Superior Gallaecia and the University of Minho in Portugal, as well as Islamic Azad University in Iran and Oxford Brookes University in the UK, as shown in Table 4.

In addition, among the journals in which the authors publish, Renewable and Sustainable Energy Reviews and Sustainability (Switzerland) are the two most influential, with a total of 282 and 268 citations, as shown in Table 5. It is also evident from Table 5 that Elsevier is the most active publisher in vernacular architecture. In view of the increasing number of publications on vernacular architecture in the last two decades, the 20 most highly cited journals are counted, as shown in Table 7, and a qualitative and systematic analysis can more effectively distil the research contributions of scholars. In this regard, this study recapitulates and organises all the contents analysed to contribute to theoretical, methodological, and practical aspects and to broaden the perspectives of future researchers, as illustrated in Figure 8.

4.2. Status of Vernacular Architecture and Its Resilience

To better answer research question 2, “Which are the most influential countries, institutions, and authors that discuss how vernacular architecture relates to cities?”, this study analyses the status of the vernacular architecture field. The results show that vernacular architecture is disappearing, and knowledge about its construction practices is gradually being forgotten [14]. This concern about the disappearance of traditional architecture and the emergence of new architecture is shared by both developed and developing countries. Dramatic changes in traditional cultural landscapes threaten multiple values and identities such as species, habitats, knowledge types, and landscapes [10].

For the performance of vernacular architecture in today’s urbanisation, a large portion of scholars focus on the fields of energy assessment, climatology, and seismology; for example, its utilisation of building materials and techniques available at the time to provide the most comfortable shelter [14]. Others focus on the theoretical perspectives of narratology, architectural heritage preservation, and cultural values, exploring various aspects of the physical and cultural impacts of vernacular architecture itself. Current research has largely established that urbanisation, materials, and land use influence the sustainable production of buildings as well as cities and that there is also a need to address future climate change [57].

The choice of research methods also varies. Many of the documents in this bibliometric search rely on quantitative analyses, which have the advantage of providing specific scientific contributions to the academic community and reducing the likelihood of bias. Of course, qualitative analysis is more appropriate for these elements regarding architectural values and regional culture, which can provide potential opportunities for vernacular architecture in human well-being and cultural sustainability.

Due to the different choices of methods, there are differences in practice. Part of the literature on quantitative methods deals with content such as environmental and energy indicators, which involve practical projects on energy consumption data, carbon emissions, indoor environmental quality indicators, energy challenges, etc. Also, studies addressing thermal comfort, modern design, and building technologies in the context of climate and environmental sustainability are available. Meanwhile, there are case studies for building conservation and restoration, and building seismic performance improvement. Corresponding practice in spatial planning and decision analysis is also included.

However, the preservation and cultural transmission of vernacular architecture are equally necessary and urgent. Therefore, vernacular architecture conservation, traditional building materials, technological sustainability, cultural heritage, national decision making, and land strategy are addressed in practice. In terms of cultural identity and sustainability, the presence of vernacular architecture can contribute to social and community cohesion, which can be better expressed through historically documented architectural documents and oral histories. It is undeniable that vernacular architecture is essential for resilience as well as sustainable urbanism to better survive in the twenty-first century [57]. The validity of the structural style of vernacular architecture can explain its function and principles and adapt to climate and aesthetics that are meaningful for resilience [1].

The findings of this bibliometric analysis can help practitioners in the building industry as well as scholars by providing a systematic reading archive. Thus, their professionalism in the practice of vernacular architecture can be improved in accordance with local policies and technical standards.

In summary, considering the status of vernacular architecture today, researchers need to think about climate change in the context of an unpredictable future, especially in the quest for ways in which cities can become more resilient. Not surprisingly, vernacular architecture offers a possibility to complement urban issues.

4.3. Lessons from Experience and Sustainable Development

Lessons can be learned from previous studies, allowing us to respond to research question 3, “Which are the most cited publications, and do they address the experiences and lessons learned in vernacular architecture?”. Section 3.4 provides the answer to RQ 3, and among the 20 highly cited articles listed (see Table 7), the paper Energy retrofits in historic and traditional buildings: A review of problems and methods is the most cited (n = 197). However, this article focuses on energy retrofits in historic and traditional buildings in Europe and North America with cold or temperate climates [72]. Vernacular buildings and regional traditions in other climates still need to be further explored and cultural barriers need to be overcome. A regulatory gap remains in the sustainability aspects of their proposed building retrofit guidelines and decisions. However, China‘s approach to traditional architecture has been characterised by a development strategy that adheres to international conventions while also exploring its own sustainable methods [25]. Similarly, the highly cited (n = 169) article Multiple criteria evaluation of rural building’s regeneration alternatives also discusses the economic benefits and environmental potential of building regeneration in the context of building reuse [78]. Nevertheless, the conclusion is that the solution is hardly applicable to all subjects in all countries. Thus, these gaps confirm the need for this study.

As shown by the research contributions mentioned in Section 3.4, folk architecture has been optimised through history and is worthy of study in terms of “climate adaptation”, “material technology”, and “comfort”, but traditional intelligence and responsiveness have been gradually lost [14], especially in developing countries. Therefore, the same alarm needs to be sounded from the perspective of human well-being and cultural heritage.

Vernacular buildings have evolved from the distant past to become buildings that will house future generations. Understanding them is therefore imperative [57]. The heritage of values and technical effectiveness of traditional architecture can stimulate the construction of a more sustainable future [104]. From previous experiences and lessons learned, it can be seen that spaces must be appropriately designed at the micro- and macrolevels, based on the energy required to sustain the environment to meet the modern architectural paradigm to maintain sustainability [1]. Moreover, the evidence shows that the utilisation of renewable resources and energy sources in response to the risk of climate change is also an option for sustainable development [14].

In summary, the indications highlighted in this paper and the predictions of future research trends can further the research potential of vernacular architecture, providing the possibility of integration between architectural engineering, the humanities, and the social sciences, thus contributing to the diversification and sustainable development of vernacular architecture.

4.4. Architecture in Cities and the Future of Humankind

By responding to RQ4 in Section 3.5, the keywords and themes of current global vernacular architecture research are further identified: “Energy and Thermal Comfort”, “National Countermeasures and Seismology”, “Vernacular Architectural Heritage Conservation and Sustainability”, and “Urban and Vernacular Architecture”. The study found that these are the topics and research directions of interest to practitioners and related scholars, covering the fields of engineering and humanities. In addition, according to the analysis in Table A1 of the keyword list and Figure 7 visualisation map, it can be found that “indoor thermal environments”, “remote sensing”, and “sustainability” are the most popular and interesting directions for scholars, to which future research will be related. It is also evident from the analysis of the literature data that, in order to solve the problems of air pollution and energy consumption in contemporary cities, the technologies in vernacular architecture can be utilised [3]. Such traditional techniques can benefit the residential areas of modern cities and efficiently transform the traditional strategies into sustainable and favourable conditions for human survival. Therefore, they must be further considered by both industry practitioners and researchers.

However, in the conflict between urbanisation and architectural styles, vernacular architecture must find a new identity in the city as well as in human society [10]. Through the literature, it is evident that vernacular architecture can provide strategies with feasibility for urban development. For instance, vernacular traditional construction strategies have good potential in designing urban areas that, when combined with contemporary design methods, can more effectively satisfy the daily needs of the occupants to provide more sustainable living environments [4]. Modern architecture is more likely to achieve architectural sustainability when following the design principles of vernacular types, whether in terms of ventilation, climate comfort, building materials, or technology. Thus, vernacular architecture can guide the behavioural patterns of the occupants and contribute to the sustainable development of the architecture in cities [6]. In addition, the study of vernacular architecture is intended to facilitate architects becoming more familiar with architecture and urbanisation which, in turn, can enhance the sustainability of the city [1].

5. Conclusions

This study analysed the bibliometrics to understand the evolution of vernacular architecture globally, its status, and the possibility of predicting its future development. It also reviewed and connected the resilience of vernacular architecture in cities and sustainable development for a better future of humankind. Quantitative data analysis as well as qualitative text analysis were used. Also, Boolean operations (quotation marks, OR, EID, and *) were used to retrieve documents published between 2000 and June 2023 from Scopus, the largest literature database, and data cleaning and screening procedures were performed to identify 1403 documents. The data were selected for bibliometric analysis using Microsoft Excel data operations as well as visual graph mapping, using VOSviewer. The results of the study identified: (i) Publishing Trends and Building Futures; (ii) National Contributions; (iii) Institutional Production and Networks; (iv) Production Sources and Levels; (v) Authors’ Scientific Productivity; (vi) Highly Cited Documents; and (vii) Co-occurrence of Keywords.

Furthermore, after extracting the specific contributions and the research framework, this study discussed the contributions of the research findings to theory, methodology, and practice. Then, the research questions were also discussed in detail: (i) Publishing Trends and Implications for the Future of Architecture; (ii) Status of Vernacular Architecture and Its Resilience; (iii) Lessons from Experience and Sustainable Development; and (iv) Architecture in the City and the Future of Humankind. However, the current research areas of environmental energy indicators, climate, sustainability, building conservation and restoration, and seismic performance remain. Despite the work and achievements of scholars and practitioners, it remained a challenging task to understand how vernacular building construction techniques and sustainable materials could be effectively applied to modern architecture and urban development. In this regard, this study presented the literature data on vernacular architecture and analysed and explained the shortcomings of current research to strengthen the understanding of vernacular architecture and identify areas for future research, contributing to the existing knowledge.

However, there remain limitations to this study. Firstly, despite Scopus’ large sample size, it cannot guarantee to cover all documents. Future studies could attempt to include other literature databases, such as Web of Science. Secondly, regarding the selection of visualisation tools for bibliometric analysis, future researchers may choose to experiment with Bibliometrix R and others to present different visual effects. Thirdly, as far as the scope of the literature search was concerned, this study used the most intuitive title search. However, it could be argued that the keywords searched were perhaps not comprehensive enough, so there remains scope for expansion of the retrieved document data. Finally, the analysis and exposition of the study results may not have been exhaustive, despite scientific cleaning steps being followed in the data screening process to ensure the data were solid and harmonised. In conclusion, this bibliometrics review paper makes a significant contribution to the understanding of the status, impact, and future of vernacular architecture research. It alerts and directs architectural practitioners and researchers to take more action in the field, thus providing a positive contribution to the body of knowledge on vernacular architecture.