Research on the history, ecology, and design of folk houses:A review of the literature on seaweed houses in China

ABSTRACT Ecological folk houses which are formed under the influence of the local climate, topographic features, and regional resources, are generally environmentally friendly and energy-saving with low-carbon emissions. They conform to local habits and behavior patterns. The study of ecological folk houses provides a valuable reference for the sustainable development of houses. One of the world’s most representative ecological folk houses, the “seaweed house”,was selected as the object of this study. A comprehensive review of research on seaweed houses was carried out in the Jiaodong Peninsula in China regarding their origins, historical development, structure, ecological strategies, and the conservation situation based on a bibliographic survey of more than 100 references over the last thirty years. The findings suggest that: (1) seaweed houses have a very high research value for sustainable development, which is mainly reflected in the ecology, culture, and region; (2) ecological strategies such as the material characteristics of seaweed and granite, roof slope, volume factor, and layout of the seaweed house courtyard are key influencing factors for the warmth of seaweed houses in winter and their coolness in summer; (3) the reduction in seaweed materials, unsustainable roof thatching skills, and the preference of young people for modern houses are the three main reasons for the rapid decline in seaweed houses; and (4) cultural excavation, economic development, and ecological optimization are key to the sustainable development of seaweed houses. Thus, this paper proposes possible future research and application directions.


Introduction
Using a grass roof covering is a common method for ecological folk houses globally.A "grass house" is not only highly regional but is also low-carbon and energy-saving and embodies the wisdom of early human beings to comply with nature and the environment.The utilization of grass materials in the rooves of vernacular architecture is directly related to the local natural conditions, climate, and other regional factors.In some coastal areas, one type of special folk house is known as the "seaweed house" (Figure 1), which uses a seaweed roof covering and has attracted much attention due to its excellent ecological characteristics.Historically, Denmark, the Netherlands, the United Kingdom, Japan, China, and other countries have constructed "seaweed houses", among which Denmark and China have the typical ones (Yang and Qian 2019).In 2007, the National Geographic magazine published photos of seaweed houses on the Danish Island of Laesø, which attracted public attention.Local people used driftwood and seaweed from the sea to build their homes, which became valuable architectural and cultural heritage after a hundred years (Widera 2014).The seaweed house is the characteristic folk house of the Jiaodong Peninsula in China and is one of the most representative ecological dwelling houses in the world, with a history of more than 1,000 years.Seaweed houses in China, which are warm in winter and cool in summer, are durable and flammable, ecological and livable, low-carbon and environmentally friendly (Zhang and Wang 2011b), not only have high scientific research value because of their excellent ecological characteristics but also have strong regional characteristics because they consist of a large amount of original ecological local genetic material and embody the traditional fishing civilization and wisdom of the area's ancestors (Chen 2017).Many scholars have studied seaweed houses' materials, layout, and ecological characteristics.This paper reviews the factors, historical evolution, and ecological characteristics of seaweed houses and then displays the status of their conservation and renewal.This paper aims to comprehensively summarize the research status of seaweed houses in China, provide guidance for eco-friendly building design, and provide a comprehensive reference for future research on the sustainable development of seaweed houses.

Introduction of research object
Jiaodong Peninsula is located east of the Jiaolai River in Shandong Province, China (37.23°N, 122.59°E).It is surrounded by the sea on three sides, with strong winds and frequent typhoons all year round.Jiaodong Peninsula belongs to the warm temperate monsoon type humid climate zone, with four distinct seasons, an annual average temperature of about 12°C, annual average sunshine of about 2600 h, and an annual average rainfall of about 800 mm.Jiaodong Peninsula has very superior mountain and sea resources, the seawater temperature of the seawater is extremely suitable for the growth of seaweed, and the offshore area is rich in seaweed.To adapt to the climate and shelter from the cold and wind, local residents built a type of building with a seaweed roof and granite walls, the seaweed house.The overall color of the seaweed house is light brown with gray and plain with a deep color.Seaweed houses not only embody the unique architectural culture of the Jiaodong Peninsula but also are warm in winter and cool in summer and do not rot for a century.It is a genius initiative of local residents and a typical ecological residential house that adapts to the local climate and conditions.
According to the research of scholars, the distribution of seaweed houses is historically mainly in the Jiaodong Peninsula and they are also distributed in the Lushun District of Dalian and the coastal area of the Changshan Islands in the south of the Liaodong Peninsula (Yang 2010).However, the remaining seaweed houses are concentrated in Rongcheng, Weihai, and are only scattered in other areas (Figure 2) (Wang 2016).At present, the seaweed houses in Rongcheng City are in the coastal zone, facing the sea behind the mountain.The terrain is relatively flat and the location is relatively isolated (Fan 2021).

Literature analysis
A comprehensive search strategy identified relevant studies on seaweed houses, using seaweed house books, Web of Science, Google Scholar, and the Chinese National Knowledge Infrastructure database.Except for photographic articles, literary articles and some articles that were not relevant to the theme, a total of 101 research publications on seaweed houses were summarized and studied, including books, magazine articles, Proceedings, and master and doctoral  theses.The 101 papers were marked and classified according to the main content of the study.Figures 3-4 presented the number and content of published papers.Table 1 lists and main research contents in detail according to the publication year of 101 papers.The number of papers on research on seaweed houses has increased significantly in recent years, indicating that people are paying more and more attention to this research.These papers affirm the unique value of seaweed houses.In addition, the number of published papers on the material properties of seaweed houses is the largest, which shows that scholars recognize the ecological value of seaweed house.Also, the least number of papers were on thermal performance tests of seaweed houses and there is still a lack of systematic and quantitative research on the thermal environment and building energy consumption of seaweed houses.

Fieldwork
The purpose of the fieldwork is mainly to verify the content of the literature Analysis.In the autumn of 2020 and the spring of 2022, field investigations were conducted in Dazhuangxujia Village and Yandunjiao Village in Lidao Town, Rongcheng City respectively.During the fieldwork, a large number of actual pictures of the appearance, material, layout and construction of seaweed houses were taken, and different types of seaweed houses were selected for mapping work, which provided realistic materials for the exposition part of the paper.

The development of seaweed houses
As for the historical origin of the seaweed house, scholars generally agree with Wenfu Li, who believes that the formation of the seaweed house can be traced back to the period of the early evolution of human habitation from aerial nesting to ground-dwelling and from underground cave-dwelling to ground-dwelling (Wenfu 2004).It is also believed that the semi-cave rounded rectangular house from the Beizhuang site in the Changdao area, which is restored in the Yantai museum, is the prototype of an early seaweed house (Liu 2017).However, Xiaojie Wang has questioned this and believes that the seaweed that was used for the construction of seaweed houses needs to be treated and the process of building a seaweed roof is complex (Wang 2021).Therefore, it would be impossible to had a seaweed house in prehistoric society, and the house that the Yantai Museum restored should be covered with thatch.Thus, perhaps the existing materials cannot directly point to the specific time of the origin of seaweed houses.However, it can be determined that there has been historically a tradition of building with grass roofs in the Jiaodong Peninsula.
According to the data of the Yantai Museum, during China's Warring States period, the population of the Jiaodong Peninsula gradually increased.The fisheries and salt production became large scale, so many people settled in Jiaodong, which increased the number of   The expression of "sea culture" in the architectural decoration form and culture of seaweed houses was analyzed from three aspects: the theme, material and color used in the architectural decoration.Housing with seaweed roof -vernacular dwellings in Rongcheng, Shandong Province (Yulin 2006) Journal Paper

2006
The architectural characteristics, structure, and layout of the seaweed house were introduced, and the possibility of the seaweed house being borrowed from modern architecture was also explained.Zosteric acid -an effective antifoulant for reducing freshwater bacterial attachment on coatings (Newby et al. 2006) Journal Paper

2006
Zosteric acid, a natural product found in seaweeds, was also effective in reducing the early stages of biofouling, such as bacterial attachment that leads to biofilms.Seaweed house -fairy tale world by the sea (Zhou and Liu 2007) Journal Paper

2007
The historical development, architectural shape, and culture of construction techniques of seaweed houses were introduced, and all parties in society were called upon to work together to protect seaweed houses.Visiting Chinese rare folk house -seaweed house (Liu 2007)  The idea of creating seaweed houses based on local conditions, local materials and regional cultural characteristics were discussed from the unity of ecology and modality.Selection and application of regional residential materials: Taking seaweed house as an example (Yang 2011) Journal Paper

2011
The idea that seaweed was chosen as the building material for the seaweed house was discussed due to the geographical isolation, abundant seaweed resources, limited production of local tiles and the developed local salt industry.Charming folk house -Weihai Seaweed House (Jiang 2011)  Journal Paper

2015
The ideas of seaweed house conservation were proposed, included inheriting folk culture, enhancing villagers' awareness of conservation, increasing publicity and increasing the practical functions of seaweed houses.Research on the Regional Construction Mechanism and Method of the Traditional Seaweed Houses (Wang 2016) The whole process of building a seaweed house was analyzed dynamically and continuously by used the method of architectural illustration, and the regional mechanism and method of seaweed house was studied in detail.The research on the characteristics of local-style dwelling houses in coastal areas of Jiaodong (Jin and Wang 2016) Journal Paper

2016
The historical development and architectural characteristics of seaweed houses were discussed, while development strategies were proposed, included the regeneration of seaweed materials, the addition of practical functions and the reuse of alterations.Research on the regional construction mechanism and design method of the new type of seaweed house (Zehuan 2016) Dissertation 2016 A idea of building a new type of seaweed houses was proposed from three aspects, the modernization of seaweed materials; the modern interpretation of traditional construction and the use of modern structural systems.The construction of eco-village--Taking Weihai seaweed house as an example (Jianfeng and  The regeneration design strategies of the seaweed house were proposed through the analysis of its architectural form, spatial structure and materials, combined with the design of dongchudao Village Folk Museum. (Continued) seaweed houses.Gradually, villages appeared and the construction technology improved (Wang 2011b).
During the Qin and Han dynasties, ancient Chinese architecture also significantly expanded.The construction technology of seaweed houses became increasingly mature, and the pattern and appearance were shaped (Zhang and Chen 2011).Therefore, the period after the Qin and Han dynasties and before the Song and Jin dynasties can be determined to be the formation period of seaweed houses.Seaweed houses flourished in the Yuan, Ming, and Qing dynasties (Longjuan 2020).The historical materials from Rongcheng City, it was stated that during the yuan and Song Dynasties, many military strongholds were built as coastal defenses in the Jiaodong Peninsula, which brought many soldier farmers.Soldier farmers stationed in the Jiaodong Peninsula increased the number of residents in the seaweed house villages and some of them settled there; thus, the seaweed houses developed and prospered (Zhou and Song 2012).Most of the existing seaweed houses were preserved or inherited from this period.For example, in the southern part of the present Ningjinso village, many seaweed houses were inhabited by soldier farmers in the Ming Dynasty (Yang and Zhu 2008).

The current situation for seaweed houses
Since entering the modern era, the construction form of folk houses in the Jiaodong Peninsula has changed with the rapid development of the social economy.Many modern buildings have replaced many seaweed houses (Jingwen 2013).For example, in the Rongcheng area in Shandong Province, which has the largest number of seaweed houses, a census of seaweed houses was conducted in Rongcheng City in 2006, and there were still 95,000 seaweed houses (Dong, Xuechang, and Guo 2017b).However, according to the findings of scholars such as Jiandong Gao (Gao et al. 2017) and Xingbiao Chu (Chu, Xiong, and Peng 2012), now the total number is less than 10,000.Moreover, they are scattered in many natural villages (Jin and Wang 2016).Yulin Li and others believe that seaweed houses will silently disappear if reasonable protection and continuation measures are not taken (Yulin 2006).
Among the 101 articles studied in this paper, about 16 articles discussed the reasons for the loss of the seaweed houses.Among them, mainly based on the discussion of Wenfu Li et al., include the following three points: (1) offshore aquaculture has destroyed the growth environment of wild seaweed, and coupled with seawater pollution, wild seaweed is becoming scarcer, which leads to the price of seaweed soaring; thus, a seaweed house has become a "luxury house" (Chen 2018); (2) as the thatchers have no successors, the roof thatching skills for seaweed houses are being lost (Wenfu 2007); and (3) due to modern buildings having more complete functions than seaweed houses, young people are seldom willing to live in the old seaweed houses (Yang 2020).Consequently, many seaweed houses have collapsed, leaked, or disappeared because of being uninhabited for a long time (Zhou and Cheng 2013).

Material variation of seaweed houses
When building a seaweed house, the basic construction materials are seaweed, wood, and large granite stone.The seaweed material (Figure 5) is generally Zostera marina L. and Zostera noltii Hornem., which grow in the offshore area about 5-  10 m from the coastline.Seaweed is used for the roof, wood for the beams, doors, windows, wood carvings, and furniture, and granite stone is used for the walls and decoration.Then, auxiliary materials are also needed such as yellow mud, mountain grass, and wheat straw (Zhang 2020).The construction materials of seaweed houses are constantly updated and changing.Table 2 illustrates the changes in the building materials of seaweed houses from the Qing Dynasty to modern times (Tianyi 2008).With development over time, the quality of seaweed house construction is constantly improving, and residents' desire to improve their living standards is also developing.

Natural resource factors
Abundant and easily obtained seaweed and granite stone materials are convenient factor in producing of seaweed houses.They are also an important embodiment of seaweed houses adapting to local conditions.In the past, mature seaweeds were swept up the beach by the waves and were easy to obtain along the coast (Cong 2009).The geology is mainly composed of granite, with hills and mountains accounting for more than 70% of the total area.The Jiaodong Peninsula is also an important stone production area in China, and it can be obtained by direct digging and from local materials (Tan 2020).Yang Jun et al. demonstrated the selection of seaweed house materials and believed that the main factors affecting their selection were manifested in three aspects.First, the geographical isolation of the Jiaodong Peninsula deepened the dependence on local materials (Yang 2011).Second, the soil in the Jiaodong Peninsula is gravelly, and the viscosity makes it difficult to make tiles, which leads to a limited output of local tiles (Chen 2020).Therefore, the local houses did not use tiles as roofing materials.Third, the local salt industry is highly developed, and the limited wood is used to make salt (Yao 2017), which promoted granite to become the main load-bearing wall material.

Climatic factors
The Jiaodong Peninsula has a temperate monsoon climate, with cold wind and snow in winter and heavy rain and typhoons in summer.It is a cold area with high annual air humidity, a large amount of precipitation, and frequent sea fog (Lin 2019).Thus, the local people had to confront the local climate to survive better and consequently, the high ridges of the seaweed house facilitate drainage and snow removal and the thick granite walls can resist the wind and rain (Jun et al. 2018).Furthermore, the insulation effect of the seaweed roof and the good thermal stability of the thick stone walls make seaweed houses warm in winter and cool in summer for comfortable living (Yu Wang and Tong 2013).In comparison, the mud houses and the wooden houses in the plain area could not withstand the strength of the sea breeze (Jiang 2011).

Social and cultural factors
Liu Zhigang and other scholars have conducted indepth research on the cultural connotation of seaweed houses, which can be summarized into four parts: (1) Traditional Chinese thought, (2) Religious Culture, (3) Folk Culture, and (4) Garrison Culture.
(1) Traditional Chinese thought Chinese traditional thought is mainly reflected in the site selection, layout, and structure of seaweed houses.The regular and symmetrical courtyard layout reflects the Traditional Chinese feudal ritual hierarchy system and the traditional thought of balancing Yin and Yang (Xiang 2012).The mellow and thick seaweed roof represents that "the heaven was spherical", and the rectangular or square courtyard represents that "the earth was square", which is the embodiment of the Traditional Chinese thought that "the heaven was spherical whereas the earth was square" (Kuang and Yu 2013).Additionally, the site selection principle of seaweed houses being built between the mountains and the sea follows the Traditional Chinese thought of Feng shui (Shao 2015a).
(2) Religious Culture Historically, the Jiaodong area was known as a comprehensive place of religious belief, especially for Buddhism and Taoism.There is often a Buddhist Hall in the interior layout of seaweed houses, while the locals like to pray with incense and worship Buddha (Liu 2007).Taoist thoughts and folk customs in the Jiaodong Peninsula are integrated.The seaweed house, whether it is the overall village planning or the indoor and outdoor layout of a single building, will reflect the Taoist thoughts of pursuing and living in harmony with nature (Hao 2018b).
(3) The folk culture of seaweed houses The folk culture of seaweed houses can be roughly divided into marine culture and construction customs.The construction of seaweed houses goes through the process of choosing the base, laying the base, laying the wall and upper beam, placing the purlin, placing the rake, thatch fixation of the roof, installing the doors and windows, and installing the base pot platform adobe Kang and brushing it white (Liu 2014).Each process reflects the unique construction customs of seaweed houses.Moreover, Jiaodong residents have had the marine customs of "offering sacrifices to the sea" and "worshipping Mazu" since ancient times.The fish-shaped and wave-shaped carvings on the doors and screen walls of seaweed houses (Figure 6) and the themes of marine creatures that are often used for interior decoration, not only represent "totem worship" (Zheng and Henan 2005) but also reflect the unique marine culture in Jiaodong folk houses.Furthermore, the custom of sharing the gable in seaweed houses (Figure 7) symbolizes the solidarity of fishermen in the face of the ocean, which is the embodiment of marine culture (Wang and Wang 2018).
(4) Garrison culture According to the folk customs of Rongcheng, the residents of seaweed houses can be divided into two categories, the coastal fishermen and the "soldier households" that historically migrated from Rongcheng and other areas for coastal defense.Qing Mei, Tingting Rong, and others studied the influence of garrison culture on the formation of seaweed houses.They believe that the nature of military households and their families profoundly impacted the layout of seaweed houses (Mei and Wang 2017) and made the house more elegant and orderly (Rong 2018).There was one seaweed house with brick walls and ground bricks for stitching and exquisite craftsmanship in Dongchudao village, although locals indicated that it was a public barn built by officials in the Ming Dynasty (Jiang 2013).

The site and plane layout of seaweed houses
Seaweed houses are located in places facing the sea and backing the mountains and are built based on the angle of the slope (Chen and Ying 2012).This site selection limits the seaweed houses' construction area but allows each seaweed house to obtain sufficient lighting and ventilation (Zhang and Liu 2018).The layout of seaweed houses is closely related to Jiaodong's folk customs, living habits, and geographical and climatic conditions (Shao 2015b).Usually, the seaweed houses are arranged in a group of 3-5 in a horizontal arrangement with a shared gable and the layout is tight and the courtyard is narrow.This layout is used because the mountainous and hilly terrain of the Jiaodong Peninsula makes the sites that are available for village construction relatively tight, and they can withstand cold weather well (Zhang 2015).
The layout of seaweed houses continues the form of traditional Chinese folk houses with middle axis symmetry (Wang and Chang 2015), which can be divided into five forms: a single house, one main suite and one wing room, a three-side enclosed courtyard, a four-side enclosed courtyard, and a two-tier courtyard (Figure 8).The more complex the layout, the higher the construction cost.Among them, the single house is the simplest layout of the seaweed houses, with its interior generally having three or four rooms.The three-side enclosed courtyard is widely used by ordinary residents; it consists of the main house in the middle of the buildings and two wing rooms on the east and west sides.The main house has three to four rooms and the wing rooms have two or three rooms (Zhang 2020).
The main house is the master's room and the wing rooms on the east and west sides fulfill secondary functions such as storage, a kitchen, or a guest room.Generally, in the traditional courtyard layout, the west wing room is the storage room, toilet, or kitchen and the east wing room is the guest room (Yang 2021).Families with better financial resources usually choose the four-side enclosed courtyard, as it adds a row of halls on the south side compared to the three-side  enclosed courtyard.The two-tier courtyards are relatively rare and are usually the houses of large families or were rebuilt on the original base due to the separation of brothers in the family (Zehuan 2016).The layout of seaweed houses in any form is very regular, without uneven changes, with clear primary and secondary functions, and with clear functions.The main house is usually 3.5-3.6m deep and about 3 m wide.According to the research of Yahui Zheng and other scholars, the depth of the seaweed house is usually 3.3 m or 3.5 m, while the width is generally 2.1 m, 2.4 m, 2.6 m, or 3 m (Zhen 2020).

The plan and structure of seaweed houses
The overall shape of the seaweed house is peaked and towering.The arrangement of seaweeds on the roof is high at both ends of the ridge and low in the middle, forming a saddle curve with ups and downs (Jianfeng and Liu 2016).The ridge height of the seaweed house to the eaves height maintains a large ratio, usually within the range of 1:1 to 1:1.5, which makes the roof slope of the seaweed house very large (Liu 2018).The roof style of seaweed houses can be divided into two forms, four sloping roofs (Figure 9) and two sloping roofs.The two sloping roofs are the common roof style that is used by seaweed houses and the thickness of seaweed on the roof is between 0.8 and 1.5 m (Liu 2016).Usually, seaweed houses with the roof style of four sloping roofs are 3 m wide and 4 m high, are built close to the corner of the gate in the courtyard, and their main function is to act as a mill or pile up sundries, firewood, and agricultural tools (Tuoka 2012).
The structure of the roof of the seaweed house is complex (Figure 10).First, the beam frame bears the foundation of the whole roof.Second, the purlins are laid on the beam frame and then the guard board is laid on the purlins.Third, straw mud is wiped on the guard board, then it is covered with thick seaweed, and finally, the roof is pressed with tiles or thicker seaweed (Wang 2020).The roof trusses of a seaweed house are made of wood, usually in the form of a triangular structure.The walls of the seaweed house are mainly divided into the adobe wall, stone wall, and brick wall.The soil slope and stone wall thickness are generally   >40 cm, and the partition wall in the middle is usually built with adobe brick and coated with straw mud (Liu and Yang 2016).Some supporting structures of the seaweed house are made from brick, for example, the upper part of the south gable wall, both sides of the courtyard gate and porch, the corner of the wall, and window frames and eaves (Huang 2014).

The building skills for seaweed houses
The building skills for seaweed houses are quite complicated.One seaweed house needs to go through three steps of material preparation, wall building, and roof covering, requiring the cooperation of four types of bricklayers, carpenters, stonemasons, and thatchers, and totaling more than 70 manual processes (Chu, Xiong, and Peng 2012).The specific construction process sequence can be divided into four steps, (1) site selection and laying the foundation, (2) building the walls, (3) installing the roof frame, and (4) thatching the roof (Figure 11) (Wang and Lei 2018).
Thatching the roof is the distinctive craft in the construction of a seaweed house, with a long history and uniqueness and is called the "thatching craft" by local craftsmen (Chen and Mengchao 2020).The process of this "thatching craft" has been studied in depth by Xinyu Liu and others, including the four stages of sheet backing, roof cover, slope, and ridge press.Starting from the guard board, seaweed and straw are overlapped, the former in the outer layer and the latter in the inner layer, then they are covered layer by layer, pressing the top of the seaweed with mud, and finally, thatching is conducted up to a height of more than 1-3 m (Liu 2019).The thatching layer must be high and steep to remove water and prevent rainwater from seeping into the roof (Huang 2014).However, in recent years, the "thatching craft", as a highly valuable building skill, is facing extinction because it must be inherited through the traditional method of master and apprentice and because of the decreasing number of seaweed houses (Gao, Wang, and Yongjian 2017).

The ecological strategies of a seaweed house
Seaweed houses are original ecological buildings that not only have the advantage of being mildew-proof, moth-proof, fireproof, windproof, and damp proof, but are also warm in winter and cool in summer, comfortable to live in, and can last for a hundred years (Hongyan and Dai 2017).In addition, experiments have shown that seaweed houses have very good durability and generally only need to be renovated once every 40-50 years (Zhang and Wang 2017).This is because the ecological strategies that are used for seaweed houses are well adapted to the local climate.The existing literature on the relevant ecological strategies can be summarized as consisting of the following five aspects.

1). Material properties
When it comes to the material characteristics of seaweed houses, scholars recognize that seaweed's excellent ecological performance as a building material.Among them, Yang Jun and other scholars showed that the Zostera marina as thatching material for seaweed houses has excellent ecological properties.First, it was found that Zosteric acid is one of the antibacterial substances in Zostera marina and can fight bacteria and reduce the attachment of barnacles (Newby et al. 2006), which makes the roof effective for insect prevention and corrosion resistance.Second, Zostera marina fiber does well in tenacity and increases the wholeness of the roof so that it is adapted to the strong wind in the Jiaodong Peninsula.Third, the unique organism cellular structure of seaweed which has more abundant air spaces than wheat straw, means that seaweed rooves have more insulation space.Additionally, the method of thatching the roof optimizes the material combination; the layer of seaweed layer with rich colloids forms a firmer outside layer, while the straw layer serves as a loose air space inside, like a big thermal barrier (Yang 2012).Fourth, the Zostera marina has obvious flame retardant characteristics.Furthermore, the Zostera marina is a naturally degradable material, which becomes soil nutrients without polluting or damaging the environment.According to the residents of seaweed houses, the sound insulation effect is better than a general brick and tile house, stating that "living in the quiet seaweed house, even when it rains heavily, you cannot hear the sound.You can sleep well at night without a jingling drum sound on the roof (Quantao and Han 2012)." The granite stone walls with a thickness of more than 40 cm have good thermal stability.In summer, the roof blocks the thermal radiation, preventing a rapid indoor temperature rise.At night, the sea and land winds in the coastal area take away the heat that is stored in the roof and stone walls.In winter, the thick material absorbs the sun's rays and keeps the indoor temperature stable (Chen 2002).Also, seaweed houses use natural building materials and are free from any pollution, which greatly benefits to the residents' health (Xiaolin 2008).Notably, Liu Zhigang and other scholars found that residents of seaweed houses have a longer life span and include many centenarians.

2). Reasonable site selection and orientation
Jiaodong Peninsula is a mountainous and hilly area.Seaweed house villages are built on sunny slopes, facing the sea and with gentle terrain (Figures 12-13).The purpose of this site selection is to use the mountain in the north to block the cold wind and play a role in keeping the house warm in winter and cool in summer while receiving sunshine from the south (Chen and Mou 2014).They are usually oriented about 15° south by east.They are well adapted to the local sun azimuth, thus making full use of the sunlight while still reducing summer sun exposure and improving indoor thermal comfort (Liu and Chenchen 2015).
3).Reasonable roof slope It is common for the slope of seaweed house roofs to be over 50° and some have thatching of up to 2 m or more (Zhang and Zhou 1996).The soaring roof slope can effectively lead the cold wind in winter to the upper air (Figure 14), reduce the wind speed in certain areas, greatly improve the drainage efficiency, and reduce snow cover (Yan and Aimin 2012).Thus, it is well adapted to the winter's cold and snowy weather in the Jiaodong Peninsula.

4). Reasonable housing scale
The main house of a seaweed house follows a rectangular plane.It has a large width, about 9-12 m, which is beneficial to increase heat gain in winter.It also has a small depth, about 3.6-4 m, which reduces the heat gain in the east-west interface in summer and indoor heat loss in winter.Moreover, the shape coefficient of the main house in this layout is about 0.6, which can effectively reduce the heat dissipation area and improve the indoor thermal environment (Liu 2015), reflecting the insulation culture in the Jiaodong Peninsula.

5). Reasonable layout of the yard
The courtyard of the seaweed house is usually small in size, with a length of about 9-12 m from north to south and a width of only 4-8 m from east to west.The courtyard's width is only 1/3 of the width of the main house, therefore playing an effective role in adjusting the microclimate.In winter, the   narrow courtyard helps to protect from the coastal winter wind (Tong et al. 2020).In summer, there are usually several deciduous trees in the courtyard (Hao 2018a), which form a "cool courtyard" blocking the direct sunlight with leaves, which not only effectively reduces the wind speed but also improves the environment and adjusts the microclimate in the courtyard area (Figure 15).

The thermal environment of a seaweed house
Yan Wu, Xiang Liu, and other scholars have tested and verified the thermal environment of a seaweed house.In January and August, Xiang Liu measured the temperature and humidity for a month and evaluated the thermal environment using the PMV (predicted mean vote) -PPD (predicted percentage of dissatisfied) value.He concluded that the indoor thermal comfort was average in winter and good in summer.After comparing the temperature of seaweed houses with that of brick-tile houses on cold days and hot days, Yan Wu concluded that the heat insulation performance was better than that of brick-tile houses (Yan 2012).

Conservation and development of the seaweed house
Over hundreds of years, the seaweed house formed its unique cultural value and thus should be preserved and developed.Research on seaweed house protection and development can be roughly divided into three aspects: village protection and development, house renewal and protection, and development and utilization.

Protection and development of seaweed house villages
Regarding the preservation states of different seaweed houses villages, scholars agree on the overall classification and protection strategy, which two main representative researchers describe.Jiandong Gao graded and scored 63 seaweed house villages in Rongcheng city based on four evaluation indexes: (1) architectural evaluation, (2) site selection and pattern, (3) intangible cultural heritage and humanistic value, and (4) current situation and development resources.It was proposed that a first-level protected village with a high total score in value evaluation should protect all the buildings, roads, public spaces, and landscapes within the village scope and a second-level village with a medium total score in value evaluation should plan to protect the buildings, roads, and important public nodes in key areas.Then, a third-level village with a low total score in value evaluation should protect the concentrated seaweed houses, traditional streets, and lanes with characteristics and important public nodes (Gao et al. 2017).Jinjian Ma integrated the protection and utilization value of the 63 seaweed house villages using four aspects: (1) site selection and layout, (2) construction, (3) cultural characteristics, and (4) development potential.It was also recognized that the protection mode of traditional seaweed houses villages can be divided into three types, overall protection, area protection, and street protection.Then, the suggestion of joint planning to form groups and the differentiated development of seaweed house villages was suggested (Jinjian, Gao, and Xiaotian 2019).
In addition, regional development strategies should be adopted for sustainable development and targeted development strategies should be chosen according to the actual situation of each village.Shengge Wang et al. graded and rated seaweed houses in six traditional villages in Lidao Town, Rongcheng City.They found that the population size and economic income were the two main factors influencing village vitality, while resident retention and tertiary industry development were critical to development (Wang et al. 2017).Jian Zhang believed that sustainable development should proceed from four dimensions, the economy, society, ecology, and culture and he summarized the "TEAM model" for village development as "Tourism Destination + Ecology + APP + Maker" (Zhang 2017).Xuebiao Geng proposed the "ECAD model" for village development as "ecology + culture + art + design" and summarized four effective measures for the restoration and protection of landscape ecology, inheritance, landscape culture, the interpretation and reconstruction of landscape art, and the authenticity and innovation of landscape design (Geng 2019).Dong Ma and Dongxue Guo used the Yandunjiao seaweed house village in Rongcheng city as an example to propose that the cultural characteristics of traditional seaweed villages should be fully utilized to develop the tourism industry, which would result in a win-win situation for village protection and tourism development (Dong, Xuechang, and Guo 2017a).

The protection and inheritance of seaweed houses
There are generally three consensuses in conservation research on seaweed houses.The first is to follow the principle of "restoring the old" (Liu and Chang 2022), carrying out antique restoration while maintaining the overall architectural style with the traditional techniques and materials of seaweed houses.The second is that per the principle of integrity, the protection of seaweed houses should coexist with the folk customs of villages.The folk customs should be inherited while protecting the seaweed houses (Liu and Chen 2015;Zhao 2017), and the protection of the village landscape should also be emphasized (Xu et al. 2014).The third is establishing an ecological museum, which has active protection and inheritance functions, to effectively protect seaweed houses (Lv 2020).
In terms of inheritance, first, in recent years, there have been studies and practices conducted on the artificial cultivation of seaweed in the Rongcheng area, which will provide seaweed resources for the inheritance of seaweed houses.Second, a protection mechanism for thatchers of the seaweed houses should be established under the guidance of the government, to protect the inheritance of "thatching craft" (Zhang and Gao 2017).Third, a "new type of seaweed house" model should be explored.Changlin Shao proposed that new technology should be used to build seaweed houses based on inheritance and materials, and the functional layout should be changed to meet modern people's lifestyle and habits (Shao 2017).

The development and utilization of seaweed houses
Development is for better protection.We can promote far-reaching development by utilizing the full value of seaweed houses and realizing the benign cycle of protection, development, and utilization (Sui and Xiao 2022).At present, there are typical development and utilization methods.First, the houses are used for locals to live in.Therefore, seaweed houses need to be improved according to the needs of the local people.Wang Peng and other scholars obtained demand data from residents to improve seaweed houses through interviews with seaweed house residents.They summarized the main needs of seaweed house locals using grounded theory, which is reflected in three aspects: improving seaweed quality to prolong the roof repair cycle, improving living space quality, and developing seaweed house tourism (Wang et al. 2021).Second, combined with local tourism industry planning (Runhua, Cao, and Huo 2009), seaweed houses could be transformed into family-owned bed-and-breakfasts, restaurants, tourism and cultural centers, or other public housing.Third, a typical well-preserved seaweed house could be transformed into an ecological museum or a village history museum (Pan 2021).Scholars have generally agreed upon this method.More than half of the scholars from the literature on the utilization of seaweed houses have proposed the construction of a seaweed house folk museum.Among them, Caiyun Liu analyzed the Dongchudao Seaweed House Ecological Museum and found that the Ecological Museum could be used as an important strategy for the regeneration design of seaweed houses by using actual cases (Liu and Fang 2021).

Conclusion
The following conclusions can be drawn by summarizing the relevant literature on the 101 seaweed houses that were studied in this paper.
(1) All scholars recognized the sustainable ecological value of seaweed houses and summarized the main values of seaweed houses into aesthetic value, ecological value, regional cultural value, and sustainable development value.Among all the discussions in the literature on the problems faced by the development of seaweed houses, the reduction in seaweed materials, the change in residents' demand, and the inheritance of seaweed house building skills are recognized as three problems.Therefore, these three aspects are urgent problems that need to be solved for the sustainable development of seaweed houses.
(2) The site, plane layout, and structure of seaweed houses conform to the characteristics of typical folk houses in the cold areas of northern China.Additionally, the "thatching skill" as the unique building skill of seaweed houses, has both ecological and cultural value.(3) Ecological strategies such as the material characteristics of seaweed and granite, roof slope, volume factor, and layout of the seaweed house courtyard are key influencing factors for the warmth of the seaweed house in winter and its coolness in summer.(4) The development of regional culture is the focus of the protection of seaweed houses, the protection of the seaweed house environment is the basis for the development of seaweed houses, and the protection of seaweed houses by classification is an important strategy for the development of seaweed house villages.Additionally, cultural excavation, economic development, and ecological optimization are key to the sustainable development of seaweed houses.

Research prospects
The following research areas are suggested for the study of the ecologically sustainable development of seaweed dwellings and communities, taking into account current developments: (1) It is necessary to increase the number of studies on the measurement of the thermal environment and building energy consumption and then conduct quantitative research with computer simulation technology to explore the ecological, green, and appropriate technical principles for the ecological strategy, which can be used as a reference for modern building energy conservation technology.(2) The construction of seaweed houses should be optimized from the perspective of sustainable development architecture, expanding their cultural and ecological value to give this rare ecological folk house have new vitality in its development.
(3) We should broaden the scope of research that is conducted on the sustainable development of seaweed house villages and learn from the development strategies of similar villages with global protection development.For example, the combination of the tourism landscape and agricultural development that was adopted by the "He Zhang Zao" residential village in Baicawa Township, Japan (Wang 2016).This will establish the foundation for natural environment protection and obtain inspiration from foreign experiences.

List of abbreviations
PMV predicted mean vote PPD predicted percentage of dissatisfied Zm Zostera marina Za Zosteric acid JP Jiaodong Peninsula Tc Thatching craft

Disclosure statement
No potential conflict of interest was reported by the authors.

Funding
The

Figure 1 .
Figure 1.(a) Seaweed houses in Japan.(b) Seaweed houses in Laesø Island, Denmark.(c) Seaweed houses in the Jiaodong Peninsula in China.(d) Seaweed houses in a village in China.

Figure 2 .
Figure 2. The current distribution of seaweed houses in China.

Figure 3 .
Figure 3. Number of published papers on seaweed house.

Figure 4 .
Figure 4. Research content of published papers on seaweed house.
Monograph 2007A detailed record of the architectural style and building customs of the seaweed houses, a comprehensive review of the traditional marine culture of Jiaodong, and an analysis of the historical causes of the seaweed houses.The destruction of the ecological environment has affected the loss of folk crafts(Wenfu 2007) Newspaper article2007The point that seaweed was on the verge of extinction due to ecological pollution and unplanned and uncontrolled offshore farming was discussed, which indirectly leads to the decrease of seaweed houses.The characteristic folk house in Jiaodong, China--Seaweed House (Yang and Zhu 2008) Journal Paper 2008 The historical development, folk culture, architectural features and conservation status of the Seaweed House are discussed, along with an appeal to strengthen the protection of the Seaweed House.Study on Weihai Seaweed House Residence (Tianyi 2008) Dissertation 2008 The affected factors in the production of the Seaweed House were introduced in detail, and the construction of an ecological museum for the conservation and utilization of the Seaweed House was proposed.Field Investigation of Rongcheng Seaweed House and Research on Its Formal Beauty (Xiaolin 2008) Dissertation 2008 The beauty of the art form of the seaweed house was discussed in terms of its overall shape, architectural color, village layout, street layout, and construction techniques, and the architectural culture contained in the seaweed houses was also analyzed.The bun of the sea -the memory of seaweed house in Jiaodong (Cong 2009) Monograph 2009 The architectural forms, restoration techniques and local folk culture of seaweed houses were vividly described Exploiting traditional Jiaodong seaweed houses as tourism resources (Runhua, Cao, and Huo 2009) Journal Paper 2009 The idea of developing traditional Seaweed House as a tourism resource was proposed, and the possibility of developing family hotels, tourist resorts, and eco-dwelling Seaweed House Museum was discussed.Study on the construction of seaweed house in Jiaodong Peninsula (Yang 2010) Dissertation 2010 The evolutionary process, geocultural factors of formation and development of seaweed houses were discussed in detail, and the plan layout, structure, and construction techniques of seaweed houses were analyzed from examples.A unity of Ecology and Modality, A Construction Study of Space Pattern about seaweed house ( Research on spatial renewal strategy of coastal traditional villages in Jiaodong Peninsula (Chen 2020) Dissertation 2020 Through the case study, the specific problems and renewal design strategies of the traditional village of seaweed houses in the process of renewal and transformation are presented.Study on the Planning and Design of the Protection and Renewal of Jiaodong Haicaofang Village (Xu 2020) Journal Paper 2020 Seaweed house village renewal design and conservation strategies were proposed, including restoration of the old and integration of modern living habits.Research on the Protection and Development of Traditional Villages from the Perspective of Folk Culture--A Case of Seaweed Cottage in Rongcheng, Shandong (Yang 2020) Journal Paper 2020 Taking Xiaoxi Village in Rongcheng, Shandong Province as an example, a strategy to protect and develop the seaweed house villages by combining different folk cultures with residential houses, tourism and festivals respectively was proposed.Research on The Protection and Innovation of The Construction Technique of Yandunjiao Sea straw House in Jiaodong area (Zhang 2020) Dissertation 2020 The history, culture and construction techniques of seaweed houses were discussed in detail, and strategies for the preservation and innovation of seaweed house construction techniques were proposed in terms of spatial planning and construction materials.Aesthetics Creation of Seagrass Dwellings in the Jiaodong Peninsula ancient craftsmanship of seaweed houses were analyzed, including the construction of the overall environment, the construction of a single building, and the technology and craft of "Shan Seaweed".Research on Digital Protection and Inheritance of the Traditional Architectural Techniques of Seaweed House in Jiaodong (Wang 2020) Dissertation 2020 The idea of using database construction and digital museum to preserve the traditional architectural techniques of seaweed houses was proposed.Construction Technology of Seaweed House in Dongchudao Village, Weihai (Chen and Mengchao 2020) Journal Paper 2020 The specific process of building a seaweed house was analyzed in detail.Ecological Characteristics, Protection and Renewal of Seaweed Houses as Special Residences in Jiaodong Peninsula (Tong et al. 2020) Journal Paper 2020 The article reviews the research progress of the protection and renewal of seaweed houses, and the protection of seaweed house villages, and proposes the strategy of protecting and renewing the sea cottage villages and houses.Some Reflection on the Construction of Seaweed House Traditional Village Ecomuseum in Weihai (Lv 2020) Journal Paper 2020 The idea of building an ecological museum of traditional seaweed houses to preserve and develop seaweed houses was proposed.Era exploring value of sea straw house in Rongcheng, Shandong (Sui and Xiao 2022) Journal Paper 2021 The ecological value, aesthetic value, cultural value and living value of seaweed houses were discussed.Study on the protection and tourism development model of seaweed house village in Jiaodong area (Pan 2021) Journal Paper 2021 The necessity of seaweed houses village conservation and tourism development was elaborated, and the idea of developing rural eco-cultural tourism model by giving full play to the cultural characteristics of seaweed houses was proposed.Historical research on Jiaodong sea thatched houses and their construction techniques of reflecting on the previous "Neolithic theory" of the origin of seaweed houses, the view that the seaweed houses can be proved since the beginning of the Yuan and Ming dynasties was proposed.Research on the Influencing Factors of Villagers' Living Demand in Seaweed Cottage Based on Grounded Theory --A Case of Rongcheng (Wang et al. 2021) Journal Paper 2021 Using programmed rooting theory, a model of influencing factors of seaweed house residents' needs was constructed to provide a reference for the construction and maintenance of seaweed houses in the Jiaodong.Research on regenerative design of Jiaodong dwellings-East Cubroussonica Island Folk Museum as an example (Liu and Fang 2021) Journal Paper 2021

Figure 6 .
Figure 6.The fish-shaped and wave-shaped carvings on the screen walls of a seaweed house.

Figure 8 .
Figure 8.The layout of a seaweed house.

Figure 9 .
Figure 9.The roof styles of a seaweed house.

Figure 10 .
Figure 10.The structure of the roof of a seaweed house.

Figure 11 .
Figure 11.The construction process sequence of building a seaweed house (Wang and Lei 2018). .

Figure 12 .
Figure 12.Seaweed house villages built on sunny slopes, facing the sea, and with gentle terrain.

Figure 13 .
Figure 13. the mountain in the north is used to block the cold wind in winter and for cooling in summer.

Figure 14 .
Figure 14.The soaring roof slope leads the cold wind in winter to the upper air.

Table 1 .
Publications that were included in the literature review.
Origins Research on Thatch Technology of Seaweed Roof Houses in Dongzhe Island Village (Huang 2014) Journal Paper 2014 The "thatching craft" of seaweed houses and its' historical origins was discussed in detail.Discussion on the Strategy of Jiaodong Seaweed Houses Heritage Protection (Chen and Mu 2014) Journal Paper 2014 Ideas for the conservation and development of seaweed houses were proposed: continued the architectural form; expanded the use function; improved the quality of spatial environment and regenerated seaweed materials.(Continued)

Table 1 .
(Shao 2015a)The advantages of natural and cultural landscape resources for the tourism development of the seaweed house villages were discussed, while the view that the priority of landscape protection must be adhered to in tourism development was put forward.Architectural Properties and Applications on Seaweed Dwellings of Orient Shandong Province(Shao 2015a) Research on the ecological strategy of traditional settlement streets and lanes based on microclimate environment--Taking Jiaodong seaweed house settlement streets and lanes as an example (Liu and Chenchen 2015) Journal Paper 2015 The ecological strategies of the street space of the seaweed village were mainly reflected in the reasonable building orientation, street height and width ratio and street alignment through field study and computer simulation analysis.Study on Microclimate of Seaweed Houses in Jiaodong--A case of Dongchudao Village (Liu 2015) Dissertation 2015 The evaluation results of the overall comfort of the microclimate of the seaweed house village of Dongchudao were obtained.The ideas of energy-saving renovation of seaweed houses were proposed in terms of both envelope structure renovation and functional layout optimization.Inheritance and Protection of Seaweed Houses in the Weihai Area--Taking Rongcheng City as an Example (Liu and Chen 2015)
A study on the relationship between the city of Weihai coastal defense station in the Ming Dynasty and the military defense of seaweed house villages under its influence (Mei and Wang 2017) Conference Paper 2017 It was proposed that the influence of military defense ideology on the village of seaweed houses was reflected in the site selection, planning layout, architectural form and architectural decoration of the village.(Continued)

Table 2 .
Construction materials of seaweed houses., pinewood, yellow mud, shellfish grass, and sorghum straw.Late Qing DynastyCompared to the previous period, green brick, white mud, wine bar fences (local vines), and paper were added.The Republic of China Era Cyan gray brick, pine, lime, cement, and glass were added to the previous period.The present Metal components, red bricks, reed foil, and wood were added to the previous period.

on contributors Ms. Yi Liu is
study has been supported partly by the China National Key R&D Program Research on the energy efficiency and health performance improvement of building operations based on lifecycle carbon emissions reduction (Grant No. 2018YFE0106100) , Shandong Province Key R&D Program on Development of the Healthy and Low carbon Residential House with Smart Home Environment Management System (Grant No. 2019GSF110003) a doctoral student in the School of Environmental and Municipal Engineering at Qingdao University of Technology, China.Her major field of study is green building and municipal engineering.Dr.Weijun Gao is a tenured professor at the University of Kitakyushu, Japan and Academia Professor, Qingdao University of Technology, China.He has been a visiting professor at many universities including China and USA, such as Xi'an Jiaotong University, Zhejiang University, and Lawrence Berkeley National Laboratory, USA.Professor Gao's research interests include: the science, engineering, management, and dissemination of city environment planning, distributed energy system, building material recycle, health and environmental impacts of energy generation and use, geographic information system, climate change, especially in urban area, and energy forecasting.

Dr. Xingtian Wang is
the honorary dean of the School of Architecture and Urban Planning at Qingdao University of Technology and has served as a researcher at Waseda University in Japan, as well as the chief architect and director at a renowned design firm in Japan.He is also the principal architect at Shanghai Xingtian Architecture and Engineering Design Firm.