Architectural Institute of Japan
Translated Paper
Technological developments of Japanese prefabricated housing in an early stage Shuichi Matsumura,1 Tomoyuki Gondo,1
Kouichi Sato,2 Yoshiro Morita3 and Toru Eguchi4
1 Department of Architecture, Graduate School of Engineering, The University of Tokyo, Tokyo, Japan; 2Department of Architecture, Kanazawa Institute of Technology, Nonoichi, Ishikawa, Japan; 3Department of Architecture, Faculty of Engineering, Tokyo Polytechnic University, Atsugi, Kanagawa, Japan; 4 Department of Architecture and Urban Culture, Graduate School of Urban Innovation, Yokohama National University, Yokohama, Kanagawa, Japan
Correspondence Shuichi Matsumura, Department of Architecture, Graduate School of Engineering, The University of Tokyo, Tokyo, Japan. Email:
[email protected] Funding information Japan Society for the Promotion of Science, Grant/Award Number: 22656128 The Japanese version of this paper was published in Volume 78, Number 693, pages 2307-2313, https://doi.org/ 10.3130/aija.78.2307 of the Journal of Architecture and Planning (Transactions of AIJ). The authors have obtained permission for the secondary publication of the English version in another journal from the Editor of the Journal of Architecture and Planning (Transactions of AIJ). This paper is based on the translation of the Japanese version, with some slight modifications.
Abstract Major prefabricated housing manufacturers started their business in the 1960s and became world-class large housing companies. This study clarifies the early stages of development in 9 major prefabricated housing manufacturers based on interviews with their in-house engineers and architectural designers as well as through the analysis of related documents. Early prefabricated houses were developed intensively by a small number of engineers. Various architectural styles and specialists, including foreign architecture, famous architects and academics, affected some aspects of these developments. Furthermore, each of the early prefabricated houses had many unique building system characteristics. Some of these characteristics were modified in the early stages of development, while others still remain today. Keywords building system, interview, pioneer days, prefabricated house, R&D
Received May 2, 2018; Accepted August 11, 2018 doi: 10.1002/2475-8876.12064
1. Introduction
company histories, the drawings of early developments, and the existing housing examples.
1.1 Background and purpose
Japanese prefabricated housing manufacturers are unlike any others in the world; they were founded a half century ago, and now supply over ten thousand houses a year. They developed unique building systems between the end of 1950s and early 1960s despite the fact that there was no existing precedent for this type of housing in the Japanese housing market; their building systems have continued to grow until this day. Each company’s history does not adequately describe the early developments of building systems because the company’s history was not always focused on these developments, although some company histories may partially deal with them. Furthermore, investigating the details of the early developments through interviews with engineers who were in charge of them will become even more difficult in the future. In this circumstance, this study aims to clarify how Japanese prefabricated housing manufacturers developed their housing products in the early stages of the housing business and what the benefits of their approaches were. To verify these points, we extensively interview the engineers in charge of the early developments and examine their
1.2 Survey targets
The survey targets of this study are 9 major prefabricated housing manufacturers in Japan. Table 1 shows their names and early housing products. In this study, we refer to the period of developing and selling these housing products as the early stage of the housing business for each manufacturer. 1.3 Methods
This study uses the document research and interview methods. The former extracts evidence of the early developments of the 9 major prefabricated housing manufacturers from each company’s history, the company’s brochures of early housing products and the issues of a housing industry magazine published in the 1970s. The latter is carried out with engineers in charge of the early developments, [Note 1] except for the engineers of two manufacturers, Eidai Company and S x L. 2. Preceding studies and context of this study
Fundamentally, the company histories and founder’s biographies of major prefabricated housing manufacturers refer to
This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. © 2018 The Authors. Japan Architectural Review published by John Wiley & Sons Australia, Ltd on behalf of Architectural Institute of Japan. Jpn Archit Rev | 2018
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Table 1. Nine major prefabricated housing manufacturers investigated in this study Structure
Company name (former name)
Early product (sale starting year)
Steel frame construction
Daiwa House Industry Company
Steel frame construction
Sekisui House (Sekisui Chemical Company)
Timber panel construction Steel frame construction
Eidai Company PanaHome Corporation (National House industrial Company split off from Matsushita Electric Works Company) Misawa Homes Company (Misawa Wood Company) S x L (Kobori Jyuken Company) Asahi Chemical Industry Company Sekisui Chemical Company Toyota Home Company (Toyota Motor Company)
Midget House (1959) Daiwa House Type-A (1962) Sekisui House Model A (1960) Sekisui House Model B (1961) Eidai House Type-One (1960) Matsushita Type-One (1961)
Timber panel construction Timber panel construction Steel frame construction Steel frame construction Steel frame construction
the developments in the early stages of their operations in the housing business. However, these histories and biographies do not focus on the building systems and the personal ideas and experiences of the engineers in charge of their early developments, [Note 2] who played an important role in developing the early building systems through working as part of a small team in a short timeframe. Nevertheless, there are 3 important preceding studies related to this study. A representative study of building systems developed by Japanese prefabricated housing manufacturers from the 1960s to 1970s is included in the AIJ (Architectural Institute of Japan)’s book.1 This book explains the progress of prefabricated houses in Japan and illustrates details of representative building systems. On the other hand, Togo’s2 and Matsumura’s3 studies examine the emergence of the prefabricated housing industry in Japan and the technical differences in the early building systems through a review of changes in Japanese prefabricated houses. 3. Features of early development 3.1 Background of development 3.1.1 Specialized field of umbrella companies
The 9 companies had their own various backgrounds in the development of prefabricated housing systems. The variety of backgrounds of the 9 companies that started the development of prefabricated houses can be seen particularly in (i) the specialized field of their umbrella companies and (ii) in the companies’ usage of the umbrella companies’ technique [Note 3]. Misawa Homes Company, Eidai Company, SxL and Daiwa House Industry Company are the companies whose umbrella companies were related to the architectural field: the predecessor of the Misawa Homes Company was a timber distribution company; the Eidai Company specialized in the manufacturing of wooden building materials; SxL’s predecessor was engaged in the design and construction of wooden houses; and the Daiwa House Industry Company was engaged in supplying temporary buildings constructed of steel pipes. They started to develop prefabricated houses in response to the growing demand for housing at that time. Among these four companies, Misawa, Eidai and SxL adopted wooden paneled building construction systems. The remaining 5 companies were from large industries or a non-architectural field, such as the chemical, electrical products, and automobile [Note 4] industries.
Misawa Home Free Size (1962) Kobori New Home (1968) D Series (1970) Sekisui Heim M1 (1970) Office & Shop (1975) Type-JA (1977)
3.1.2 Usage of the umbrella company’s technique
Among the 5 companies, Sekisui House and Asahi Chemical Industry Company tried to divert new materials developed in a non-architectural field into housing construction. Sekisui Chemical Company started to develop prefabricated houses with the aim of developing new applications of plastic material products, and Asahi Chemical Industry Company developed prefabricated houses in the process of trying to find usage for “Silikalitsit,” an ALC (Autoclaved Lightweight Concrete) panel introduced from the Soviet Union [Note 5]. As mentioned below, these two companies abandoned their efforts to apply the new materials, such as plastic and Silikalitsit, to structural uses and finally attached them as much as possible to steel structures. Meanwhile, Toyota Motor Company and Matsushita Electric Works Company began the development of prefabricated houses in order to seek new fields in which to apply their existing products and technologies. According to the documents of Toyota Home Company, Toyota was very serious about finding applications for their automobile technologies, and the application development was conducted jointly with their associated enterprises, such as Aisin Seiki and Nippondenso, who contributed their own expertise (Figure 1). Additionally, in the case of the National House Industrial Company, their intention of applying their existing products can be recognized in the testimony stating that “The aim is to develop and commoditize ideal houses with great habitability by utilizing equipment and building material products comprehensively,” while also stating “We shouldn’t apply plastic materials too much nor persist in our past products” and “Human habits and preferences must not be ignored.”8 3.2 Influence from other cases and persons
Prefabricated houses in the early days were developed with few reference structures. Under this situation, prefabricated housing development was influenced by precedent cases published in documents, by architects and by research conducted outside the company. 3.2.1 Idea from documents and other works
Sekisui House Model A was a typical case in which the idea for the home was obtained from documents. The development of Sekisui House was started based on inspiration from an article about an all-plastic house from the Monsanto Company [Note 6]. Additionally, a person in charge of the Jpn Archit Rev | 2018 | 2
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Figure 1. The development plan of Toyota Home in the early days. (The document “The Agenda of Toyota Home” from Toyota Home (in the interview on December 21, 2011) shows that the companies that joined the development of prefabricated houses by Toyota Motor Company were Nippondenso, Aishin Seiki, Kanto Auto Works, Toyota Forms, Toyota Boshoku, and Toyota Motor Sales. Figure 1 shows that the pilot house was divided into several parts and that each company developed their own parts, such as the kitchen developed by Nippondenso and the Japanese room and closet MAC (Movable Assembled Component) developed by Toyota Forms. The word MAC means closet of functions, an original word used by the Toyota Home Company.)
Model A development remembered that he used the frame of the Occupation Army housing (Quonset hut) as a reference when the decision was made to change the structural material from plastic to steel [Note 7]. Moreover, the engineer of Daiwa House adopted the double-door system in their housing based on an image of European buildings in films [Note 8]. In the case of Matsushita, the Type-One model followed the design of Japanese traditional modular systems to coordinate the size between components [Note 9], which provided the possibility of reusing tatami and doors in other buildings. 3.2.2 Influence from the prefabricated architecture in western countries
Some engineers were influenced by prefabricated buildings in western countries. For example, National House Industrial Company was affected by the system and concept of the building components of “Trocken Montagebau,” a structure Walter Gropius proposed in the 1920’s in Germany [Note 10]. Sekisui House was inspired by the prefabricated steel construction system for elementary schools in the 1950’s and early 1960’s in England. Toyota Home paid attention to the high factory production rate of mobile homes in America, and Eidai Company learned from the rationality of the wooden frame construction system in America. 3.2.3 Architects and researchers in Japan
There were some cases in which architects outside the company provided advice about developments. Some of the typical ones included the following: Katsuhiko Ohno, a young architect in his twenties at that time, who was requested to propose the basic concept of the development itself (Sekisui Chemical Company); Kazuo Shinohara, who was asked to advise on the variety of units (Toyota Home Company); Kiyoshi Ikebe and Kenji Hirose (National House industrial Company); and Yukio Furuya, a former member of the firm of Kenji Hirose (Asahi Chemical Industry Company). Jpn Archit Rev | 2018 | 3
Additionally, as research institutes, Nihon University (Toshio Sato Laboratory) conducted structural experiments for Misawa Homes Company [Note 11], Osaka University (Kenzo Washio Laboratory) and Kyoto University (Kiyoshi Kaneta Laboratory) guided National House Industrial Company in structural testing and analysis, and Meiji University (Yoshikazu Kanou Laboratory) advised Asahi Chemical Industry Company on structural experiments. In addition, support from private organizations was also received. The engineer of Daiwa House Type-A reflected that he had received much advice from Fuji Iron & Steel through their drawings of office and factory buildings of light gauge steel structures [Note 12]. 3.3 Relationship between organizations
A close relationship between companies was also seen in the early stages of the development of prefabricated houses. In the case of steel structure houses, the staffs of Daiwa House Industry Company took a leading role in the development of prefabricated houses in the Toshiba Housing Industry [Note 13] and in the development of Kubota House (later renamed Sanyo Homes). This relationship was manifested in the situation in which the umbrella company of the former company was in charge of selling the Daiwa Midget House and in which the structure system that the latter company adopted was quite similar to that of Daiwa House. Sekisui House, which became independent from Sekisui Chemical Company, accepted staffs of the company for employee trainings in developing Sekisui Heim M1. Sekisui House advised Asahi Chemical Industry Company, which has the same corporate origin as Sekisui House, to shift from an agency selling system to a direct selling system.12 In the case of wooden structural houses, as the original companies in the industry, Eidai Company and Misawa Homes Company had influences on the others. The influence of Eidai Company was significant, particularly to local builders, because the company established a franchise system covering 1200 builders [Note 14] in the1970’s. Additionally, in 1978, the company had a wide influence on the industry when most
MATSUMURA et al. Table 2. Development organization in early days Present name of the company Daiwa House Industry Company
Sekisui House
PanaHome Corporation
Misawa Homes Company
Asahi Chemical Industry Company
Toyota Home Company
Summary of development organization
Midget House was developed in 1 month by one engineer in charge. He was the only staff member in the laboratory established in 1959. The engineer with 2 construction staff members started the development of Daiwa HouseType-A, and a few new recruits joined in April 1961 The Plastic House project started in September 1959. The development team was composed of two engineers, including one new recruit. The test house was built in January 1960. Sekisui House Model A was completed in March 1960, and the sales began in April. The development of Sekisui House Model B started around July 1960, and the first building was completed in June 1961 in which the engineer lived as part of an experiment. The sale of the Model B began in July The Matsushita Type-One was developed by a 4-member team that was led by an engineer with a career as an architect. The development plan was shown in November 1959, and the first test building was completed in March 1960. The test buildings were constructed 5 times a year, for which an iron foundry of the engineer’s brother often helped. Three in-house divisions were competed for the project The idea occurred to the founder when he was in the hospital. The test panel was made in January 1961. The first test building was constructed in Shin-Etsu factory, and the second in the founder’s home area in Shibuya, Tokyo. The performance test of the building was conducted in Nihon University in July 1961, and the collapse test was conducted in March 1962. Sales started after the approval under Article 38 of the Building Standards Act was granted in 1962 The study group for Silikalitsit housing was organized by the Silikalitsit division and engineering department in 1966. Type D of the steel frame construction system with a non-bearing ALC panelwas developed by 2 engineers in almost one year. One of them studied RC structures in the university and was placed in charge of the structure construction system, and the other engineer was placed in charge of the interior and equipment The department for new business was established in the planning office around October 1967. Four engineers started to study housing in 1969. A halfscale structural model was made in May 1968, and a full scale one in April 1969. A 2-story test building designed for a dwelling experiment was made in 1971. A test building designed for a structural experiment was constructed in 1973
of its engineering staff moved to Mitsui Home and other companies after the company filed bankruptcy. Misawa Home helped a certain number of housing organizations to mature, including some leading-edge suppliers of conventional wooden
wileyonlinelibrary.com/journal/jar3 Table 2 (Continued) Present name of the company Sekisui Chemical Company
Summary of development organization
The development team was formed by 6 to 7 staff members with no architectural background. Katsuhiko Ohno, a graduate student in the University of Tokyo at that time, joined the team as an architect. The company decided to move in on the housing market in October 1968. The first test building was constructed in January 1970 and the second one was constructed for a dwelling experiment in May, which was demonstrated at the first Tokyo International Good Living Show in October 1970
houses and prefabricated housing companies, such as SxL, [Note 15] which used to be one of its agents. 3.4 Organization and duration of development
Some engineers stated that the development organization was small and the duration of the development time was short in the early days compared to the situation today. For example, the Daiwa Midget House was developed in 1 month by the one engineer in charge. The development team of Sekisui House Model A was composed of two almost new recruits and, according to the business diary at that time, they performed a wide range of functions, including the study of weathering details, structural analysis, meetings with constructors, a quantity survey and process planning. The development process of the National House Industrial Company was unique, as the company allowed 3 teams to compete for the project. The company made no less than 5 test products a year for Matsushita Type-One. Table 2 shows the development organization of each company in the early days. Eidai Company and SxL are omitted in the table because the interview with them was not available. 4. Characteristics of products 4.1 Structural system
The major theme of early prefabricated house development was the structural system and the building system of some products were totally revised in the early stages of the development. Daiwa house tried to develop the building system of the Midget house (1959), which is less than 10 sqm and was designed as an additional children’s room; the Super Midget house (1960) design just included the addition of a kitchen and a toilet. However, the Daiwa House Type-A adopted different building systems than the Midget house. For example, the length of the span of the roof panel was limited because the panels were on ridge beams and girders and if the ridge direction is extended, columns would have to be placed inside the rooms. Therefore, the Daiwa house adopted a king post and then attached a panel truss arrangement to form a roof truss (Figure 2, left). Regarding the exterior wall structure, panels of the Midget house were put into two light gauge channel steel back-to-back columns between which the Daiwa House Type-A connectors (C-shape, almost square) are inserted (Figure 2, right). Jpn Archit Rev | 2018 | 4
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Figure 2. Daiwa House Type-A (left: roof truss, right: column connector). (The picture on the left is extracted from the booklet of the Daiwa House Type-A model; the figure on the right is extracted from “Drawing and Specification for factory-prefabricated house by Housing Loan Corporation” for the Daiwa House Type-A model.)
The Sekisui House Model A adopted a 3-hinge steel frame arrangement in which the strength of the column-beam joint was seen as a disadvantage. Thus, the Sekisui House Model B adopted a different structural design system: the steel-frame and the roof panels are positioned on the frame in an arrangement similar to a platform construction. The development of Sekisui House Model B had begun in July 1960, just 3 months after the Model A release, and the basic specifications were finalized in January 1961. Model B is still the prototype of their current system, which has been modified through continuous improvement. Asahi Chemical Industry Company originally did not study the use of a steel framework but rather focused on the ALC bearing wall as a structure in which the wet bearing wall system connected the walls with cast-in-place reinforced concrete bond beams on the roof sides. They constructed and commoditized experimental houses in the Itabashi-ward in Tokyo in 1967 (Figure 3). However, they experienced some problems with that system in the construction phase [Note 16], so they started to develop another system consisting of steel frames with ALC walls, which is the prototype of their current system, and they constructed the first D Series model house in the Kamata housing exhibition parks in Tokyo in 1968. The steel material was also revised. Asahi Chemical Industry Company initially welded lip channel steel back-to-back H-shaped beams. However, there were some problems, such as the interference of the ALC walls with the margin of the lip channel steel welding. Therefore, the company decided to use lightweight, H-shaped steel [Note 17]. In the drawings of 1972, the two kinds of beams that were used in parallel for a period of time can be seen. The lightweight, H-shaped steel was used for the second floor beams to support large loads and the steps between floors, and lip channel steel was used for the roof floor beams that supported less loads (Figure 4). The structural systems of the 9 companies are roughly divided into steel framework and timber panel construction. Every company was conscious of the differences in the building systems of the other companies. Furthermore, some of the original structural systems that were developed earlier are still maintained today. Three steel framework companies (Daiwa House Industry Company, Sekisui House, National House industrial Company) Jpn Archit Rev | 2018 | 5
developed their original system by taking the other companies’ structural system into account: the Sekisui House system is a steel framework arrangement with interior and exterior wall panels attached on site; in Daiwa House Industry’s design system, the interior and exterior wall panels are finished in their factory and constructed on site [Note 18]; and the National House Industrial company’s system design consists of a lightweight steel rigid frame. In these 3 companies, those differences in the framework structure are maintained in their current main products. Moreover, as Daiwa House Industry installed exterior walls on site, some other companies temporarily used a similar type of construction in some of their housing products. In timber panel construction, although the company recognized that its functionality was not good, the Misawa Homes Company continued to use the double-sided panel since the double-sided panel can prevent warpage after construction and to differentiate this company from other companies, such as the Eidai Company, which had adopted single sided panels. The features of these structural systems have been maintained until recently because each company continued development with the awareness of its differentiation from other companies and because their production facilities and sales methods had been adapted to the products that were developed early (* 21). 4.2 Module 4.2.1 Module
Since the components of prefabricated houses are produced at factories, their modular design was important in their development, from the viewpoint of both planning and construction [Note 19]. Many modules of the early prefabricated houses were different from the standard dimension of 910 mm of the Kanto module (conventional on the east side of Japan), such as the 800 mm (Sekisui Heim M1) module, the 960 mm (Matsushita Type-One) module, and the 1260 mm (Daiwa House Type-A) module. Subsequently, the modules’ dimensions were changed to approximately 910 mm because of problems such as building materials and narrow sites [Note 20].
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Figure 3. The ALC bearing wall experimental house (left) and its construction (right). (These pictures of the ALC structural wall houses are from the documents from the Asahi Chemical Industry Company. The picture on the right is the construction site for a customer, not for a prototype.)
Figure 4. D Series model section detail (1972, left: second floor beam, right: roof floor beam). (Extracted from the drawings from the Asahi Chemical Industry Company.)
The Sekisui Heim M1 model (1970) adopted the 800 mm module (2400 mm by 5600 mm). The Sekisui Heim M3 model (1975) changed its internal dimension to the 900 mm module used for 8 Tatami rooms [Note 21]. The Matsushita Type-One 960 mm module was influenced by the Kansai module (conventional on the west side of Japan), as mentioned above. Furthermore, the National House Industrial Company changed its module from 960 mm to 900 mm in their “R2N - 900” module type (1972), based on requests from their sales division to respond to the housing needs for narrow sites in Tokyo. The Daiwa House Type-A model adapted the 1260 mm module because general distributed building materials of 4-shaku by 8-shaku (1 shaku = 30.3 cm) are common in that module, and reducing the amount of steel in the wider spans reduces the costs; 3 modules, which represents 3780 mm, equals 12-shaku (two-Ken), which is consistent with the dimensions of Tatami rooms and was common to Japanese houses. The Daiwa House Type-B (1967) model changed to the 940 mm module to fit the small size of sites. This 940 mm module is equal to half the length of two 910 mm panels plus
one 60 mm width connector. Table 3 summarizes the modules seen in the target prefabricated houses and the reasons for their usage. 4.2.2 Modular coordination
The system of modular coordination in those prefabricated houses differs for each company, as pointed out by Togo.2 Regarding the 3 leading companies’ adoption of lightweight steel frame systems, while the National House Industrial Company uses a double grid adapted from the Kansai module, the Daiwa House Type-A uses an axial grid and its reference line is based on the center of the structural members. In the Daiwa House Type-A model, no irregular panels are required even at both external and internal corners since the width of the connector between panels is the same as the thickness of the panel. Sekisui House uses an axial gird and the reference line is located inside the structural members, which means that irregular panels are not required at either the inner or the outer walls, except for the internal corner [Note 22]. An engineer of Sekisui House who was involved in the development mentions the reason they could respond individually using irregular Jpn Archit Rev | 2018 | 6
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components even at the internal corner was the simplicity of the planning of their products in the early stages. 4.3 Joint of components
The joints of the components were also an important issue in the development. There were many changes in the relatively early stages of development because of the workability and strength of the joints. Regarding workability, Sekisui House originally manually punched a bolt hole and changed to press processing due to large position error [Note 23]. Daiwa House Type-A used a steel cover plate at the panel joint because of waterproofing and an error adjustment that was due to constructing their factory finished panels at sites, as mentioned above. The attachment of their panel joints was changed for design reasons to a wet sealing method in 1975 and changed to a method using dry gaskets in 1981. Regarding the strength of the joints, the Sekisui Heim M1 model adopted a rigid frame structure and used bolt joints until their second prototype was developed (May 1970). However, with the introduction of the third prototype, the structure was changed to weld joints because of the weakness of the framework joints [Note 24]. In the development of the rigid frame Table 3. Distinctive module type and reasons Product name
Module (reasons)
Daiwa House Type-A
1260 mm (to fit the panel of 4-shaku by 8-shaku and to reduce the amount of steel frame to an amount suitable for Japanese houses, as three modules equal 12-shaku) 1000 mm (shift to the meter module from the Japanese Shaku module) 960 mm (face control system, which is common in the Kansai module. Module was changed to 900 mm according to sales division’s request in 1972) 800 mm (width of the unit is 2400 mm due to the Road Traffic Law; from M3, the internal dimension changed to 900 mm.) 610 mm (fits the dimension of Hebel panel)
Sekisui House Model B Matsushita Type-One Sekisui Heim M1 D Series
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of the National House Industrial Company, spring lock washers were used to prevent the joint bolts becoming loose (Figure 5). An automobile factory was the source of a clue to the engineer [Note 25]. When the Misawa Homes Company acquired approval by the Housing Loan Corporation in 1966 (the regulation started in 1964), the strength of the adhesive on site construction was not approved. Therefore, in order to obtain the strength by using only nails, they increased the width of the frame members from 18 mm to 30 mm. 4.4 Design and use
Early prefabricated houses sometimes reflected designs that directly expressed the newness of materials and the new principles of construction methods. Typical examples were the Sekisui House Model A, which used aluminum sheets on the exterior walls as well as transparent PVC corrugated boards on the sleeve walls, and the Sekisui Heim M1 model, which emphasized the shape of a modular box. Concerning use, in the early days of development, there were several products designed for uses other than use as a general detached house. Typical examples were the Midget House of the Daiwa House Industry Company, the Eidai House Type-One Study Hut (May 1960, Figure 6, left) of Eidai Company, which was developed as a children’s room for expansion in the garden, and the Kobori Compos Honey of the Kobori Jyuken Company, which was developed as a holiday cottage [Note 26]. Sekisui House developed a gas bath hut for public housing units without an inner bath, and it was marketed by Osaka Gas Company (April 1961, Figure 6, right). It could be built in 5 hours with a total construction cost of 60 000 yen. The standard floor area was 900 mm by 1800 mm, and a dressing space could be added. Sekisui House received 300 to 500 gas bath hut orders of per month, which were supposed to compensate for the sluggish sales of the Sekisui House Model A.6 The sales of the Eidai House Type-One Study Hut were going well, and the person in charge of its development said, “At the end of the fiscal year, it could be seen that trucks carrying the study huts from the factory went on sale” [Note 27]. It seems that those products, which had limited use, could support the operations of the early unstable prefabricated housing manufacturers [Note 28].
Figure 5. Spring lock washer. (Diagrams were extracted from the noninflammable assembling house qualification documents (1962) for Matsushita Type-one, by the Housing Loan Corporation.) Jpn Archit Rev | 2018 | 7
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Figure 6.
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Left: Eidai House Type-One Study Hut N33), Right: Gas bath hut. (Extracted from “Creating the housing culture6 (1990),” p. 38.)
4.5 Sales systems
Currently, the sales systems of prefabricated houses are roughly divided into two types, namely, direct sales and agent sales. Following the interviews, two types of sales systems could be seen from the beginning of the housing business of each company. On the other hand, there were several companies that have completely changed their sales system. As a typical example, although the Daiwa House Industry Company used the agent sales method in 1957, it changed from the sales system to a direct sales method by setting up 40 direct sales offices during the period of 1973-1974 and had 120 direct sales offices in 1975 because many sales agents canceled their contract with Daiwa House due to the oil shock in 1973.5 One of the other examples is the Asahi Chemical Industry Company, which started its business using agent sales but changed to the direct sales method because the sales exceeded their construction capacity. Another example is Toyota Home Company, which initially asked Toyota Motor’s car dealers to be their sales agents but changed to the direct sales method to better manage the expansion of their sales volume. In the case of Asahi Chemical Industry Company, its commission pay system used for agent sales pushed the salesmen into a hard sales competition resulting in too rapid an increase in contracts. As its result, construction delays occurred in 70 construction sites in October 1972, and the company finally decided to stop sales activities for a while [Note 29]. Moreover, there were special advertising methods employed before the nationwide spread of the housing exhibition parks. For example, the Daiwa House Industry Company as well as the PanaHome Corporation exhibited and sold their housing products in department stores in the early stages of development. Misawa Homes Company exhibited their houses at Nihon University, which collaborated with the company in the development phase.z 5. Conclusion
This study has conducted interviews with engineers that developed the building systems of 9 major prefabricated housing manufacturers during the early stage of the prefabricated housing business and examined each company’s history and their drawings associated with their early development. In conclusion, the following has been clarified. First, this study has concretely identified the approaches 9 major prefabricated housing manufacturers applied to develop their housing products, the architectural sources that influenced their early developments, the team members that participated
in the development and the timeframe associated with the development. Each manufacturer’s approach for the development of prefabricated houses was different from that of the other manufacturers because the approach depended on each manufacturer’s business field and the available technology. Although the prefabricated housing manufacturers started their early developments of housing products to make effective use of their new materials and the company’s skills, some of them eventually transitioned out of these first manufacturing objectives. Basically, each of the 9 major prefabricated housing manufacturers developed their early housing products by use of a small team in a short-term timeframe, while obtaining cooperation or advice from architects, researchers of universities and other prefabricated housing manufacturers. At the same time, some housing developments strongly depended on the personal experience and knowledge of engineers in charge of the project. Second, the prefabricated housing manufacturers immediately changed a remarkable exterior design of their early housing products, the so-called Prefab style, into the ordinary one.3 This was related to the modification of their building systems; the unique structural components that was used in systems, such as the Sekisui House Model A or the Midget house, was changed into a post and beam construction system of light gauge steel, and the unique module size, such as 800 or 1260 mm, was changed to one of approximately 900 mm, similar to the Japanese conventional module size. In addition, some of the manufactures changed their sales organization from an agency system to a direct sales system in the early stage of housing business. Although these important changes of structural system, planning module size and sales system occurred immediately, some of the steel building systems established by 3 pioneer companies in their early business stage became not only a key point of differentiation from the competitive housing products but also a basis of their sales and production systems and remain so to this day. Acknowledgements The authors express special thanks to the funding source by JSPS KAKENHI grant number 22656128 and all interviewees and those who supported this research.
Disclosure The authors have no conflict of interest to declare. Jpn Archit Rev | 2018 | 8
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Notes Note 1) The interviewees are as follows; Yoshiharu Yoshimura, Takeshi Togo, Yoshiaki Iwasaki, Munemitsu Kimura, and Teruaki Ouchi (Daiwa House Industry Company), Yukichi Fukui and Tokusaburo Ishimoto (Sekisui House), Ichiro Abe (Eidai Company), Akio Kobayashi (PanaHome Company), Yoshiya Kato and Tomohiko Nomizo (Misawa Homes Company), Hajime Saito, Kazunori Fujimoto, and Atsushi Hasegawa (S x L), Katsuhiko Sato and Hiroshi Sakuma (Asahi Chemical Industry Company), Shohei Kaneko (Sekisui Chemical Company), Yoshikazu Kawai and Osamu Ito (Toyota Home Company). The names of the companies referred to are the names of the companies at their time of description. Note 2) There are a few examples of interviews with the engineers who developed prefabricated houses; in rare cases, we can read the interviews with the engineers in the archives of The Sekisui Heim M1,4 and several company histories of prefabricated housing manufacturers5–13 include some examples of developments or the detail of the building systems. Note 3) Panasonic Electric Works Company could be regarded as a building material supplier because they sold manufactured materials. However, their main business was manufacturing electrical products. The wooden panels by the Misawa Wood Company can be regarded as new materials; however, the innovation is the building system itself assembling wooden panels. Note 4) The responses to the questionnaire on housing assembly14 (1961) show that several companies sold assembled houses, such as steel companies (Kawatetsu Corporation, Fuji Iron and Steel), trading companies (Mitsui and Company, Mitsubishi Corporation) and a real estate company (Hankyu Real Estate). Note 5) Asahi Chemical Industry Company imported Silikaltsiit (autoclaved lightweight concrete) from the Soviet Union, and the Silikaltsiit research group was established by Norio Yoshida in June 1966. This research group became the housing division of the company. However, because of the low productivity of Silikaltsiit, the company imported HEBEL from the Hebel Gasbeton Company in West Germany in 1966). Note 6) Kazuo Suda, who was the board member of Sekisui Chemical Company (the vice director of the building material department), informed company President Ueno of the “all plastic experimental house (Monsanto Co.)” featured in the magazine of “Modern Plastics (the June and July 1957 number).” Thus, Sekisui Chemical Company started the development of prefabricated houses (“Creating the housing culture6 (1990),” pp. 12-14). Note 7) From the interview with Ishimoto, it was revealed that the building system of the Sekisui House Model A is similar to that of the Quonset Hut with respect to not only their vault structures but also to the overhang of the vault surface at the edge of the vault. Note 8) From the interview with Yoshimura. Note 9) The modular coordination of the traditional “Kyoma” tatami system is a double grid system that measures 3 shaku 1 sun 5 bu (1 shaku = 30.3 cm, 1 sun = 3.03 cm, 1 bu = 3 mm) by 6 shaku 3 sun (=960 mm 9 1920 mm). The Matsushita Type-One model adopted this system from their fifth test version because residents and building contractors were used to this system (Kobayashi15 (2001), p. 65). Note 10) Kobayashi, who developed the Matsushita Type-One model, attended the OLV meeting at the Shigebumi Suzuki laboratory of Osaka City University (“LV” is the name of the meeting at the architectural planning laboratory in the University of Tokyo, and the “O” was added to represent Osaka) and read architectural books, such as the “Scope of Total Architecture (Gropius),” at the OLV meeting (Kobayashi15 (2001), p. 7). Note 11) The experiment by Toshio Sato laboratory was reported in Saito16 (1963). Note 12) From the interview with Iwasaki. Note 13) Toshiba House Industry Company no longer exists. This company, which once manufactured the structural parts of the houses of the Asahi Chemical Industry Company and the Toyota Home Company, sold its factory to the Asahi Chemical Industry Company. Jpn Archit Rev | 2018 | 9
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Note 14) In 1964, the Housing Loan Corporation set up a review committee of factory-prefabricated houses, and it approved 6 types of wooden prefabricated houses from 5 companies: Eidai House Type-B, Eidai House Type BK (Eidai Company), Daiken Home (Daiken Lumber Industry Company), Panekyo Sweet Home (Japan Housing & Components Manufacturers Co-operative), Mitsui House Type-UK (Mitsui Lumber Industry), and Rakuda House (Rakuda Industry). Misawa Homes Company was approved in 1966. Therefore, the total sales of units of these five companies were 1850 units, and 924 units of them were sold by Eidai Company (The oral history of Hideo Sugiyama17 (2006), pp. 50-61). Note 15) Kobori Jyuken Company, affiliated with the Misawa Homes Company since 1964, started to develop prefabricated houses in the same year.11 Note 16) Quoted from “30 years history of the Housing Department of Asahi Chemical Industry Company (2003, p. 8).” From the interview with Sato, remembering the construction site of the Silikaltsiit wall structure, he said “it seemed far from mass-production, because the site was dirty. We should have made form works only for 30 cm by 30 cm beam, and set steel bars and cast concrete. It cost a lot of labor.” Note 17) Lightweight H section Steel is thin H section steel made by thermatool welding (continuous electric resistance welding). Thus, it does not have the characteristics of lip channel steel. Note 18) Iwasaki, who developed the Daiwa House Type-A, said “The building system to assemble the outer and inner walls to the structural panels have some disadvantages, such as big clearances are necessary because of on-site construction, or this clearance makes it difficult to apply dry sealing system. However, they selected this building system because of the cost or to differentiate from other companies.” The Daiwa House Industry Company started to use gasket material for waterproofing beginning in 1981. Otherwise, Daiwa assembles outer walls on site in situations requiring a heavy wall, such as in the case of “Liberte,” which used an ALC outer wall panel. Note 19) Ishimioto said “every production system was intended to adjust to the B-system. Thus, other systems cannot beat the B-system. For example, we developed the K system, but it changed to the BK system and was absorbed to the B-system.” The K system (developed on March 1971) was developed for an upscale two-story single family house, and it was Sekisui House’s first single family house type to use a bath unit (“Creating the housing culture6 (1990),” pp. 105-106, 328329). Note 20) In “20 years history of Housing Loan Company18 (pp. 304305),” it was also pointed out that “At 1962 (the start of factory-prefabricated house registration by Housing Loan Corporation), there were many kind of modules, such as 900, 910, 940, 960, 1000, 1200, and 1260 mm, depending on the companies. Gradually, many companies started to use modules close to 3 shaku (1 shaku = 30.3 cm). The reason for this change seems that the restriction from the view point of materials and small modules have advantages to make small rooms, from their sales experiences they want to increase the number of rooms in small land lots.” Note 21) The basic module of the Sekisui Heim M1 was 800 mm; the unit of the M1 was 2400 mm by 5600 mm (outer size), according to the Road Traffic Law. Beginning with the M3 module, the unit size became 2464 mm by 3840, and the basic module became 900 mm (face control). Therefore, beginning with the M3, the roofs were constructed on site.13 Note 22) Sekisui House called their grid axis the “N grid.” N grids are located on the inner surface of the outer wall (Sekisui House also counts the number of panels using “N”). Likewise, the Midget House by Daiwa House Industry Company also used the same grid system (grids are on the inner surface of the outer wall). Note 23) Ishimoto said, “Sekisui House started pressing holes after they built their own factory around 1965, so it seems close to the painting facilities.” Their first factory in Shiga prefecture started in June 1961, and the painting facility has operated since the beginning of the factory. Thus, the process of pressing holes seems to have started before 1965.
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Note 24) Quoted from reference 13. Therefore, the columns of the Sekisui Heim M1 module were directly welded to the beams, and beginning with the Sekisui Heim M3 module, both the columns and the beams were welded to the “joint pieces.” Note 25) A connection without nuts is one of the characteristics of the joints of steel members of the Matsushita Type-One. Therefore, each steel member, such as the columns or beams, has threaded screw holes. This joint system method was required to prevent loosening. Kobayashi said he arrived at the idea of using spring washers based on their use in car manufacturing systems. Likewise, the Daiwa House Industry Company used the “tap bolt,” which does not require a screw thread as a self-tapping screw does. Note 26) The National House Industrial Company also developed one unit study rooms (=10 m2) in addition to 3 unit small houses in their first pilot development program on March 1960). In the 1960s, many small prefabricated houses were developed; The “Assembling house questionnaire14” shows 63 types (14 companies) of prefabricated houses and 34 types (7 companies) are less than 10 tsubo (1 tsubo = 3.3 m2) in dimension. Note 27) From the interview with Abe. Note 28) Extracted from the Eidai Company,7 p. 99. Note 29) The company history of the Asahi Chemical Industry Company12 reveals that a delay in construction of 70 houses happened on October 1972 and stopped sales activity. In addition, in the discussion of the company history, it was revealed that the lack of the knowledge of the sales persons was the problem in the sales agent system. References 1 Architectural Institute of Japan. Prefabricated house in Japan, data book detached house. Shokokusha, 1983. 2 Togo T. Transition of the Industrialized Prefab-Housing in Japan, its Industry and Engineering. Report on industrial-technology history and systemization, Vol. 15, Center of the History of Japanese Industrial Technology, pp. 231-315, 2010. 3 Matsumura S. Industrialized House from now (Kogyoka jutaku kou Korekarano Prefab Jutaku). Gakugei Shuppan Sha, 1987. 4 The archives of The Sekisui Heim M1. Available at http://www.sekisuiheim m1.com, reference on 5th April, 2013.
wileyonlinelibrary.com/journal/jar3 5 Daiwa House Industry Company. The 30 years history of Daiwa House Industry Company, Chiseisha, 1985. 6 Editorial Committee of the Company History of Sekisui House. Creating the housing culture, 30 years of Sekisui house, Sekisui House, 1990. 7 Eidai Company. Yakushin (rapid progress in Japanese) 25 years of Eidai Company, Meibundo Printing Industry, 1971. 8 The Editorial Committee of the Company History of National House Industrial Company. 10 years of National House Industrial Company, 1973. 9 National House Industrial Company. New Living Culture ISM, 1993. 10 Market Research and Planning Division of Misawa Homes Institute for Research and Development. 40 years of technological development of Misawa Home (wooden materials), 2007. 11 The Editorial Committee of S x L, S x L Company History 1951 – 2001, S x L, 2001. 12 Asahi Chemical Industry Company and Asahi Kasei Homes Company. 30 years history of Housing department of Asahi Chemical Industry Company, 2003. 13 The Editorial Committee of 20 year history in Housing Division of Sekisui Chemical Company, The World of Sekisui-Heim. 20th Anniversary, Sekisui Chemical Company, 1990. 14 Shiroya Y; The Editorial Board. Assembling house questionnaire, Jutaku, Japan Housing Association, No.1871, 1961. 15 Kobayashi A. The Approach to the Housing Industry, National House Industrial Company, 2001. 16 Saito K, Sato T. Experimental Research on Assembling Houses by the wooden bar and panel structure, Proceeding of the architectural research meetings of Kanto Chapter of Architectural Institute of Japan, 33(1), pp.1-4, 1963. 17 The Editorial Committee of Memorial Publishing of Prof. Hideo Sugiyama. The oral history of Hideo Sugiyama, 2006. 18 The Editorial Committee of 20 years history of the Housing Loan Corporation.20 years history of Housing Loan Corporation, the Housing Loan Coorporation, 1970.
How to cite this article: Matsumura S, Gondo T, Sato K, Morita Y, Eguchi T. Technological developments of Japanese prefabricated housing in an early stage. Jpn Archit Rev. 2018;00:1–10. https://doi.org/10.1002/2475-8876.12064
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