Introduction

With rapid urbanization, rural populations worldwide are migrating to cities, and most countries and regions face a series of problems caused by the shrinking rural population. In China, the rural population has been declining at a continually accelerating rate since 19951. This trend has not only led to a decrease in the population in rural areas but also triggered a series of socioeconomic problems, such as “hollow villages”, the ageing of the rural population, land abandonment, and the deterioration of the rural environment, exacerbating the decline of rural areas2,3. In addition, the decline of rural areas has resulted in many idle and abandoned buildings. Owing to population loss, the rural building environment has been uninhabited and unrepaired for a long time, causing varying degrees of damage or even disappearance. In particular, in the case of some local characteristic buildings that reflect rural social culture, production activities, living customs, and historical development, their disappearance has a serious impact on the sustainable development of rural areas and the legacy and protection of traditional historical culture.

Many studies have analysed the decline in the rural population and the reasons for rural abandonment and decline from different perspectives or methods4,5,6. Combined with different national conditions and regional development situations, a series of relevant policies and measures have been proposed at the macrolevel7,8. The practices of some countries include Japan’s village building movement, which aims to narrow the urban‒rural gap and revitalize rural development; Germany’s village renewal, which focuses on the ecological environment, landscape protection, and cultural conditions of rural areas; and Canada’s rural partnership model, which advocates urban‒rural integration and pursues the economic and political balance of rural development9. Research on village levels both domestically and internationally, has focused mainly on their protection and development10,11,12,13, spatial distribution and form14,15,16, cultural inheritance17,18, living environment19,20, traditional architecture21,22, and spatial governance23,24,25. The study of rural idleness in China has focused primarily on the strategy of using idle space and resources26,27,28, the circulation and activation protection of idle homesteads29, and the reuse of various types of idle building spaces30,31. However, at present, there are relatively few investigations and studies on the spatial distribution and characteristics of idle buildings in rural areas at the micro- and medium levels. Additionally, there is a lack of systematic investigations and research on many idle buildings in the whole region and at the village level due to population decline and rural decay, especially for villages with historical and cultural value. Idle building spaces are often presented as the material space of village history and culture. Idle, deserted or even absent architectural space directly affects maintaining village culture at the material level, leading to a gradual decline in village culture and, at the same time, the waste of village land resources and the deterioration of the human settlement environment.

As the essence of farming civilization and the foundation of the Chinese nation, Chinese traditional villages contain rich historical and cultural information and natural ecological landscape resources. Traditional villages have a large amount of tangible and intangible cultural heritage, and architectural space is the material carrier of cultural heritage. However, under the impact of rapid urbanization and the suction of the modern city of Beijing, traditional villages in Beijing face the phenomenon of “hollowing out”. The hollowing out of villages has caused a series of problems, such as the destruction of traditional textures and architectural styles and the disappearance of traditional regional cultural characteristics32. These problems are closely related to the idle and abandoned state of many village building spaces, especially residential ones. Residential buildings, which reflect a place’s natural conditions, social conditions, and cultural traditions as well as the identity, family structure, financial resources, and knowledge of its founders, are the most basic and main type of building in traditional villages. At the same time, they serve as the prototype of other types of buildings in traditional villages. This study systematically studies idle residential building spaces in traditional villages in Beijing to provide a scientific reference for their protection and renewal. Using the ArcGIS and SPSS software platforms, this study comprehensively and systematically interprets the idle characteristics, distribution characteristics, and spatial features of idle residential building spaces in traditional villages in Beijing and analyses the relationships between spatial distribution characteristics and villages and the correlations between architectural spatial characteristics.

The current situation of residential buildings in traditional villages in Beijing

The formation and development of traditional village residential buildings in Beijing were influenced by terrain, landforms, climate, and resources and, to a certain extent, by the constraints and influences of Chinese society, culture, and the political and cultural centre of the imperial capital. The residential buildings are mainly courtyard layouts with different scales, flexible arrangements, irregular shapes, and various functions, with a focus on the comprehensiveness of spatial functions and the full utilization of space33. A comprehensive and systematic investigation of the utilization status of residential buildings in traditional villages in Beijing reveals five main categories: full utilization (not idle), partial utilization (partly idle), temporary idleness, long-term idleness (completely idle), and abandonment or collapse (completely idle). The fully utilized building space represents an optimal stage of use, which will not be further elaborated on in this paper.

Partially utilized/partially idle type

This type of space mainly refers to parts of building spaces in a building courtyard in a state of utilization and other building spaces in an idle state due to the lack of demand. In Beijing traditional villages, the spatial layout of buildings comprises one, two or multiple courtyards, with each courtyard containing one or more buildings. From the spatial layout and scale of the building space, we can roughly judge the complexity of family structures and household population size. The complexity of family structures and the different activity needs of people results in different conditions, including the desire of some to leave the village and move to the town; this results in part of the building spaces in a courtyard being idle. The main reasons and types of idle space are as follows:

A. Population decline and low space demand: Some building spaces in one courtyard type are currently in use, with varying degrees of repair or renovation. Owing to economic reasons or usage needs, there are unrenovated/unrepaired building spaces in the courtyard that have long been idle.

B. Complex property rights and part of population migration: This process mostly occurs in residential building spaces of the multiple courtyards type. Owing to complex property rights, intricate family structures, large populations, diverse economic incomes, and employment locations, some family members move to towns, and some buildings are left idle.

Temporary idle type

This type mainly refers to situations where building space remains temporarily unused for some time, with the intention to resume use later. This idleness is largely attributed to seasonal climate factors: during winter, town residents relocate to the village and return in spring, summer, and autumn. The weather in Beijing is hot and rainy in summer, cold and dry in winter, and short in spring and autumn. Due to the influence of terrain, different regions in Beijing have different climates. Generally, the piedmont plain in Beijing is hotter than the mountainous areas, making it relatively mild and comfortable during summer34. Summer suburban tourism is increasingly popular in Beijing. However, both the urban and suburban areas of Beijing are in a cold state in winter, the suburbs are colder than the urban areas are, and the winter heating conditions in villages are poor. As a result, there are generally fewer residents in some villages in winter, resulting in seasonal temporary idle building spaces.

In addition to climate, other reasons include older adults going to the city in the short-term to help their children with children, rental gap period, and business problems caused by the suspension of business. This type of temporary idleness is relatively short, the quality of the building space is good, the building functions are still used intermittently or will be used again in the near future, and the activities of people in the building spaces are in an intermittent state, which has little impact on the village’s style, resources, economy and culture.

Completely idle type

This mainly refers to the internal space, as the external space of the building is in a state of long-term unuse. That is, the entire building space is in a long-term idle state. The direct cause of idleness is the lack of human activity in the building space. The lack of human activity has led to the disappearance of the vitality of architectural spaces, and human activity has an important impact and demand on the economic use value, historical and cultural value and architectural aesthetic value of architectural spaces. When architectural spaces cannot meet the needs of people’s various activities, their vitality is lost, their economic value cannot be fully demonstrated, their historical and cultural legacy will be lost, and their architectural aesthetic value will disappear with the gradual deterioration of the architectural space. Owing to the long-term absence of use, the quality of such building spaces generally presents a certain degree of damage. The quality state is divided into three categories: slightly broken, moderately broken, and severely broken (Fig. 1).

Fig. 1
figure 1

Completely idle residential building space and the state of building quality. The author used AutoCAD 2014 software (https://www.autodesk.com/campaigns/autocad-family) to draw the plane graph, and the satellite images (the following three pictures) were taken by the author using a DJI air2 drone.

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Research object and research method

Selection of research objects

This paper study and analyses the characteristics of completely idle residential building spaces in traditional villages in Beijing, the research object of this study. Such residential building spaces are stagnant and unused, which often leads to gradual damage and collapse of the physical structure of their space. With damage to the physical structure, the historical culture and spiritual memory of the architectural space gradually disappears, which will lead to the fact that the built environment of traditional villages with unique skills and rich culture cannot be continued and inherited.

A total of 31 traditional villages in Beijing were included in the study. After preliminary investigation and statistical analysis, 529 samples of idle residential building spaces were selected. The study included six districts—Mentougou, Miyun, Yanqing, Fangshan Changping, and Huairou—and 21 towns, covering a wide range, with a certain type (Fig. 2).

Fig. 2
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Number and distribution of idle residential building spaces (IRBS) in traditional villages in Beijing. The source of Beijing map: https://beijing.tianditu.gov.cn/bzdt/.

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Research method

The main steps of this study are as follows: First, the research sample is identified through field investigation, and the relevant characteristics are collected using methods such as aerial photography, interviews, and a literature review to establish a characteristic factor system. Second, spatial layouts and forms of selected idle residential buildings are drawn using CAD and other drawing materials, with geographical coordinates determined for each research sample to provide basic data for distribution characteristic analysis. Third, the distribution characteristics of idle residential buildings are studied through kernel density estimation and quantitative analysis to derive distribution patterns. Finally, SPSS is used to analyse the spatial characteristics of idle residential building space and the correlation between each feature factor.

Characteristic factors are the basic characteristics of idle residential buildings in traditional villages in Beijing, the basis for interpreting the idle characteristics of traditional village residential buildings, and the starting point for studying the renewal and reuse of idle building spaces in traditional villages. Each factor reflects the character or value of some aspect of the idle building space. To obtain a more systematic, comprehensive and scientific understanding of the characteristics of idle residential buildings in traditional villages, a characteristic factor system is constructed at the architectural spatial level, including building location, age of construction, building level, courtyard layout, building scale and other feature factors (Fig. 3).

Fig. 3
figure 3

Characteristic factor system of idle residential building spaces in traditional villages in Beijing.

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Results

Distribution characteristics of idle residential building spaces

Using ArcGIS as a technology platform and kernel density analysis tool, the kernel density of 31 traditional villages in Beijing was calculated, and the density values were divided into 5 categories from low to high according to the natural breakpoint method: low-, lower-, medium-, higher- and high-density areas generate the kernel density distribution map of idle residential building space in each traditional village. The results of the kernel density analysis show that the distribution of idle residential building space in traditional villages in Beijing presents a medium-density agglomeration distribution overall, and some villages are characterized by local high-density agglomeration (Fig. 4).

Fig. 4
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Kernel density analysis of idle residential building spaces in typical traditional villages in Beijing. The author used AutoCAD 2014 software (https://www.autodesk.com/campaigns/autocad-family) to draw the map of traditional villages.

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Further research and analysis were conducted on traditional villages characterized by "one-core and multicore agglomeration" in the kernel density distribution map. This study, combined with the spatial morphological characteristics of traditional villages, explores the internal relationship between agglomeration distribution characteristics and village spatial layout. Elements closely associated with village spatial forms, such as the main streets, ancient roads, castles, and ramparts, have been incorporated into traditional village kernel density distribution maps. The location relationships between the cluster areas of the kernel density distribution and village spatial elements are compared and analysed, leading to their classification into the following two categories:

(1) The spatial distribution characteristics of the core density concentration area along the main street and ancient road of the village are evident, with prominent villages such as Malan Village, Weizishui Village, and Nanjiao Village. The street texture is well organized and exhibits a distinct fishbone pattern. There is a significant amount of vacant residential building space due to factors such as population decline in the village, an underdeveloped industrial sector, and delayed implementation of village reconstruction work. Consequently, residential building spaces are gradually becoming idle and abandoned along the village’s main streets and traditional ancient roads on both sides (Fig. 5a).

Fig. 5
figure 5

Kernel density-spatial form distribution characteristics of idle residential building spaces in typical traditional villages in Beijing. The author used AutoCAD 2014 software (https://www.autodesk.com/campaigns/autocad-family) to draw the map of traditional villages,

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(2) The concentration area of kernel density is mainly distributed in the village castle or the early village-forming area. The spatial layout of such villages has certain agglomeration characteristics, and the development of villages has mostly expanded around the castle and the early village-forming area, creating a relatively complete settlement pattern. Idle residential building spaces are mainly distributed in the castle and the core area of the village’s early origin. Most are traditional-style residential buildings, which were built at an early age, and the buildings were seriously damaged. The main villages include Jijiaying Village, Baimaguan Village, Zhangjiazhuang Village, Yanjiatai Village, etc. Many idle residential buildings have certain historical and cultural value, and most have not been repaired or protected (Fig. 5b).

The spatial characteristics of idle residential building spaces

Single-factor attribute characteristics

The idle space of many residential buildings in traditional villages directly reflects their excess living space and population loss. This section analyses the single-factor characteristics of architectural space elements to objectively present the characteristics of a certain aspect of idle residential buildings.

(1) Building location.

The positioning of idle residential building spaces in the village is categorized into four groups: the central area, the peripheral area, inside the castle, and outside the castle. The data indicate that idle residential building spaces are distributed across both central and peripheral areas without a clear overall trend. In Beijing’s traditional castle-type villages, most idle residential building spaces are situated within the castle, reflecting its early development as a construction area with a propensity for building space to remain unused (Fig. 6a).

Fig. 6
figure 6

Statistical analysis of the single-factor attribute characteristics of idle residential building spaces in traditional villages in Beijing.

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(2) Age of construction.

According to the statistics and analysis of the construction years of the research samples, the data show that before 1949 and from 1949 to 1979, there was a large amount of idle residential building space. Due to age of the construction, the quality, spatial layout and scale of the residential building spaces conflicted with people’s current living and production needs. This increases the likelihood of buildings remaining idle. In contrast, building spaces constructed or renovated after 1980 were tailored by homeowners to meet their specific living, employment, and economic conditions. These spaces feature comprehensive basic facilities, high comfort levels, relatively stable structures, and a low probability of long-term vacancies (Fig. 6b).

(3) Building level.

The data show that the idle residential building spaces in traditional villages in Beijing include cultural relic protection units, Puden cultural relics, historical buildings and other cultural relic buildings, as well as nontraditional style buildings constructed in the new era and more traditional style buildings with a certain completion history that reflects the historical style and local characteristics of the village (Fig. 6c).

(4) Courtyard layout and building scale.

The courtyard layout of idle residential buildings in traditional villages in Beijing is mainly a one-courtyard layout, accounting for 92%, and a two-courtyard layout, accounting for 6%. There are a few multicourtyard layouts, idle street buildings without courtyards, and single buildings (Fig. 6d).

The building scale primarily refers to the total floor area encompassing both internal and external spaces. According to statistical data on the construction scale of idle residential building spaces in traditional villages in Beijing, most of these buildings have scales below 500 square metres, with 53% falling below 200 square metres and 45% ranging between 200 and 500 square metres (Fig. 6e).

(5) Building quality and construction materials.

With the differences in idle time and building construction technology, buildings gradually experience different degrees of damage during the idle process. According to the statistical analysis, the building qualities are mainly slightly broken and moderately broken, with values of 47% and 39%, respectively. The main manifestations are broken doors/windows, roof damage/collapse, partial collapse of the courtyard and other building types of damage. There are a certain number of severely broken types, accounting for 14%, mainly because some buildings experience serious collapse, courtyard collapses and other phenomena (Fig. 6f.).

The construction materials of idle residential building spaces in traditional villages in Beijing are mostly masonry, accounting for 89%, followed by stone and red brick. Houses rebuilt with modern building materials are less idle and are generally in use or temporarily idle (Fig. 6g).

(6) Property rights.

Idle residential building spaces in traditional villages in Beijing are basically private property, that is, the qualification right and the right to use are all owned by the villagers. A few idle residential buildings belong to the village collective and the government; that is, they are public property. There is an idle residential building without the property right certificate. In cases where a residential building space lacks a property right certificate due to historical issues, reconstruction is prohibited, the space has been idle for many years, and the doors, windows and roofs of the space are damaged (Fig. 6 h).

Bivariate correlation characteristics

Moreover, we employ SPSS methodology for analysing bivariate correlations among key factors in idle residential building spaces to more comprehensively and deeply understand the spatial characteristics of idle residential building spaces in traditional villages. SPSS Pearson correlation analysis can be used to study the degree of correlation between complex variables and express it with appropriate statistical indicators35. When interpreting the results, we first look at the significance (Sig.) and then the correlation. If Sig. (two-tailed) is less than 0.05, it indicates a significant relationship between the two variables, and the smaller the significance level value, the more significant the correlation. For further analysis of the correlation, the Pearson correlation coefficient describes the relationship between two variables and the direction of correlation, and its value is between -1 and 1: -1 ≤ r < 0 indicates that the two variables are negatively correlated, r = 0 indicates that the two variables are not correlated, and 0 < r ≤ 1 indicates that the two variables are positively correlated. A value of Sig. (two-tailed) > 0.05 indicates no significant relationship between the two variables.

After the analysis results were examined, ten sets of pairwise factors exhibited significant correlations (Table 1), namely, building location and building level, building location and building quality, age of construction and building level, age of construction and courtyard layout, age of construction and building scale, age of construction and building quality, courtyard layout and building scale, courtyard layout and building quality, building quality and building level, and building quality and building scale. Furthermore, cross-tabular analysis was employed to understand the specific correlation characteristics of these pairwise factors.

Table 1 Correlation analysis results of each factor of idle residential building spaces.
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(1) Correlation analysis between building location and other factors.

Building location and building level

In castle-type villages, idle residential building spaces are distributed inside the castle, other types of idle residential building space are mostly distributed outside the castle, and traditional idle residential building spaces are mostly distributed inside the castle. In noncastle villages, the idle residential building spaces of other types are mostly distributed in the peripheral area of the village (Fig. 7a).

Fig. 7
figure 7

Statistical analysis of bi-variate correlation characteristics of idle residential building spaces in traditional villages in Beijing.

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Building location and building quality

In the four types of building locations, the three types of building quality are distributed. In non-castle-type villages, the distribution of the three types of building quality is more balanced in the central region and the peripheral area, and there is no significant difference. In castle-type villages, there is a greater distribution of idle residential building spaces whose quality is slightly deteriorated inside and outside the castles, followed by those with moderate deterioration. The number of severely deteriorated buildings is relatively small (Fig. 7b).

(2) Correlation analysis between the age of construction and other factors.

Age of construction and building level

Cross-analysis revealed that the idle residential building spaces built before 1979 were mostly traditional-style buildings, while the idle residential building spaces built after 1980 were mostly other types of buildings. The idle heritage residential building spaces were built before 1949 (Fig. 7c).

Age of construction and courtyard layout

There is no significant distribution pattern of the construction age of the idle residential building space in one courtyard type. The idle residential building spaces with two courtyards and multiple courtyards were mostly built before 1979, while after 1980, most of the idle residential building spaces were mainly one courtyard type (Fig. 7d).

Age of construction and building scale

Cross-analysis reveals that the idle residential building spaces in different construction years are mostly less than 200 square meters and 200–500 square metres in scale, with little difference in quantity. The idle residential building spaces larger 500 square metres were built before 1979, which was related to the control of the land area occupied by a homestead in China after the reform and opening up (Fig. 7e).

Age of construction and building quality

There is a significant correlation between the degree of damage to building quality and the time of construction. Moderately and severely deteriorated idle residential building spaces were mostly built before 1979, whereas the idle residential building spaces built after 1980 were slightly deteriorated (Fig. 7f.).

(3) Correlation analysis among other factors.

Courtyard layout and building scale

The building scale of idle residential building spaces in one courtyard style is usually less than 500 square metres. The building scale of idle residential building spaces with two courtyards is mainly 200–500 square metres. The building scale of idle residential building spaces with multiple courtyards is above 200 square metres, whereas the building scale of idle residential building spaces without courtyards is relatively small, at less than 200 square metres (Fig. 7g).

Courtyard layout and building quality

There are also certain differences in the building quality status of idle residential building spaces with different types of courtyard layouts. The idle residential building spaces with two courtyards are mostly moderately deteriorated, whereas idle residential building spaces with multiple courtyards are poorly preserved, mostly moderately and severely deteriorated (Fig. 7h).

Building quality and building level

Cross-analysis reveals that the building quality of idle heritage residential building spaces is slightly and moderately deteriorated and has generally been somewhat repaired. The building quality of other types of idle residential building spaces has slightly deteriorated because they were mostly built after 1980, and the time they have spent idle is relatively short. The building quality of traditional idle residential building spaces are mainly slightly and moderately deteriorated, with some severely deteriorated (Fig. 7i).

Building quality and building scale

The building quality of idle residential building spaces smaller than 500 square metres is mainly slightly and moderately deteriorated, whereas the building quality of idle residential building spaces over 500 square metres shows varying degrees of damage without significant differences (Fig. 7j).

Conclusions and prospects

Through the current investigation and quantitative analysis, idle residential building spaces generally exist in traditional villages in Beijing, and some villages have many idle residential building spaces. Through kernel density analysis, some regularity is found in the distribution of idle residential building spaces in traditional villages in Beijing. In villages with fewer idle residential building spaces, their distribution is relatively scattered, whereas in villages with more idle residential buildings, their distribution is correlated with the streets, ancient roads, castles, or early village-forming areas of the villages, and most show a linear and planar agglomeration distribution pattern.

The spatial characteristics of idle residential building spaces in traditional villages in Beijing are as follows:

  • (1) Most were built before 1979; the building level is based mainly on traditional styles; the courtyard layout is mainly one courtyard; the building scale is less than 500 square metres; the construction materials are mostly mixed masonry; the building quality is mainly slightly and moderately deteriorated; and the property right is mainly private property.

  • (2) The correlation analysis results reveal that several main factors are correlated. For example, in castle-type villages, the traditional style and idle heritage residential building spaces exist mainly in the castle. Most idle residential building spaces built before 1979 were traditional, idle residential building spaces with two-courtyard and multi courtyard layouts were mostly built before 1979, and idle residential building spaces that are moderately or severely deteriorated were mostly built before 1979.

On the basis of the preliminary study of idle residential building spaces in traditional villages in Beijing, the idle building spaces are mostly traditional residential buildings with traditional features that have witnessed the historical development of the village. They are usually located in an important position in the village, which is highly valuable for the protection and continuation of the traditional village style and the village’s historical and cultural legacy. Inheritance of history and culture. However, over time, the destruction and collapse of building spaces will accelerate and without maintenance or use, they will become idle, affecting the continuation of village culture at the material level, accelerating the destruction of the village local environment and falling further behind industrial development. Given the many idle buildings, it is necessary to systematically study the state and characteristics of the building spaces, the reason for idleness and the difficulties in exploring relevant renewal strategies and modes.

The revitalization of villages is closely related to the renewal and revitalization of idle building spaces. This reuse helps coordinate the relationship between rural people and land, activate rural land elements, activate farmers’ land assets, stimulate rural development vitality, and break the pattern of “hollowing out” of rural areas. At the same time, this is highly important for promoting the integrated development of urban and rural areas and achieving the two-way flow of urban and rural factors. This study uses a combination of qualitative and quantitative methods to systematically analyse and study idle building spaces in traditional villages in Beijing. It provides a preliminary understanding of the characteristics and correlations of idle building spaces in traditional villages at the architectural level, identifies common spatial problems in idle building spaces, and clarifies the cultural value of idle spaces. This study, as a fundamental stage achievement in the research of idle building space in traditional villages in Beijing, provides key basic research materials for the next step of studying the reasons for idle building spaces in traditional villages, the differences in idle spaces among villages, and the proposal of targeted models for updating idle building spaces according to local conditions.