《Technological developments of Japanese prefabricated housing in an early stage》
The Japanese version of this paper was published in Volume 78, Number 693, pages 2307‐2313 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.
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.
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 company histories, the drawings of early developments, and the existing housing examples.
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.
|Structure||Company name (former name)||Early product (sale starting year)|
|Daiwa House Industry Company
Midget House (1959)
Daiwa House Type‐A
(Sekisui Chemical Company)
Sekisui House Model A
Sekisui House Model B
|Timber panel construction||Eidai Company||Eidai House Type‐One (1960)|
|Steel frame construction||PanaHome Corporation
(National House industrial Company split off from Matsushita Electric Works Company)
|Matsushita Type‐One (1961)|
|Timber panel construction||Misawa Homes Company (Misawa Wood Company)
|Misawa Home Free Size (1962)|
|Timber panel construction||S x L (Kobori Jyuken Company)||Kobori New Home (1968)|
|Steel frame construction||Asahi Chemical Industry Company
|D Series (1970)|
|Steel frame construction||Sekisui Chemical Company
|Sekisui Heim M1 (1970)|
|Steel frame construction||Toyota Home Company (Toyota Motor Company)
Office & Shop (1975)
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, except for the engineers of two manufacturers, Eidai Company and SxL.
本研究采用文献研究法和访谈法。前者从每家公司的历史、该公司早期住房产品的小册子以及上世纪70年代出版的一本住房行业杂志中，提取了9家主要预制房屋制造商早期发展的证据。后者是与负责早期开发的工程师一起进行的，除了Eidai公司和S x L两家制造商的工程师。
2 Preceding studies and context of this study
Fundamentally, the company histories and founder’s biographies of major prefabricated housing manufacturers refer to 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, 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’s and Matsumura’s 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 .
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 4 industries.
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 .
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.”
与此同时，丰田汽车公司和松下电器公司开始开发预制房屋，以寻找新的领域来应用他们现有的产品和技术。根据文档的丰田公司,丰田非常认真寻找应用程序的汽车技术,以及应用程序开发其与关联企业之间进行联合,如Aisin Seiki Nippondenso,贡献自己的专业知识(图1)。此外,在全国工业企业,打算运用他们现有产品可以被识别的证词陈述的目的是开发和商品化的理想房子的适居性综合利用设备和建筑材料产品,同时也说我们不应该使用塑料材料太多,也不坚持我们过去的产品和人类的习惯和偏好不能被忽略。
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.)
丰田Home前期的开发计划。(2011年12月21日接受采访的《丰田之家议程》文件显示，参与丰田汽车公司预制房屋开发的公司有日本电装株式会社、爱新精工株式会社、关东汽车厂株式会社、丰田表格株式会社、丰田博正库株式会社、丰田汽车销售株式会社等。)图1显示了试验住宅被划分为几个部分，每个公司都开发了自己的部件，例如由Nippondenso开发的厨房和由Toyota Forms开发的日式房间和壁橱MAC(可移动组装组件)。MAC这个词的意思是“功能壁橱”(closet of functions)，这是丰田家居公司(Toyota Home Company)最初使用的一个词。)
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. Additionally, a person in charge of the 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. Moreover, the engineer of Daiwa House adopted the double‐door system in their housing based on an image of European buildings in films. In the case of Matsushita, the Type‐One model followed the design of Japanese traditional modular systems to coordinate the size between components , which provided the possibility of reusing tatami and doors in other buildings.
Sekisui住宅模型A是一个典型的案例，住宅的想法来自于文件。Sekisui住宅的开发灵感来自孟山都公司的一篇关于全塑料住宅的文章。此外，一个负责模型A开发的人记得，当决定将结构材料从塑料改为钢时，他使用了占领军住房(Quonset hut)的框架作为参考。此外，大和房建的工程师在他们的住宅中采用了基于电影中欧洲建筑形象的双门系统。在Matsushita的案例中，Type One模型遵循了日本传统模块化系统的设计，以协调组件之间的大小，这提供了在其他建筑中重复使用榻榻米和门的可能性。
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. 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.
一些工程师受到西方国家预制建筑的影响。例如，国家住宅工业公司受到了Trocken Montagebau建筑构件的系统和概念的影响，Trocken Montagebau是Walter Gropius于20世纪20年代在德国提出的一种结构。Sekisui住宅的灵感来自于20世纪50年代和60年代早期英国小学的预制钢结构建筑系统。丰田家居关注美国移动家居的高工厂生产率，Eidai公司借鉴了美国木结构建筑体系的合理性。
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).
在某些情况下，公司外部的建筑师会提供关于开发的建议。其中比较典型的有:当时20多岁的年轻建筑师Katsuhiko Ohno被要求提出开发本身的基本概念(Sekisui Chemical Company); Kazuo Shinohara，曾被要求就单位的多样性提供建议(丰田家庭公司);池部清和广濑健二(国家住宅工业公司);还有前朝日化学工业公司(Kenji Hirose)的成员yukio Furuya。
Additionally, as research institutes, Nihon University (Toshio Sato Laboratory) conducted structural experiments for Misawa Homes Company , 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.
此外,研究所,日本大学(Toshio佐藤实验室)进行了结构试验三泽住宅公司日大阪大学(Kenzo Washio实验室)和京都大学(清Kaneta实验室)引导国家家工业公司在结构测试和分析,和明治大学(Yoshikazu Kanou实验室)建议朝日化学工业公司结构实验。此外，还收到私人组织的支助。大和房型A的工程师表示，他从富士钢铁公司得到了很多建议通过他们绘制的钢结构办公室和工厂建筑的轻型规范钢结构。
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 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.
在预制房屋发展的早期阶段，公司之间的关系也很密切。在钢结构房屋方面，大和房业公司的员工在东芝住宅行业的预制房屋开发和久保田住宅(后来改名为三洋住宅)的开发中发挥了主导作用。这种关系表现在前一个公司的母公司负责销售大和小卖部，后一个公司采用的结构体系与大和小卖部非常相似。Sekisui House从Sekisui Chemical Company中独立出来，在开发Sekisui Heim M1时，接受了公司员工的培训。Sekisui House建议Asahi Chemical Industry Company(与Sekisui House有相同的企业渊源)从代理销售系统转向直销系统。
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 in the1970’s. Additionally, in 1978, the company had a wide influence on the industry when most 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 houses and prefabricated housing companies, such as SxL, 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.
一些工程师表示，与今天的情况相比，早期的开发组织很小，开发时间持续时间很短。例如，大和小房子是由一个负责的工程师在一个月内开发的。Sekisui House Model A的开发团队由两名几乎是新招募的人员组成，根据当时的业务日志，他们执行了广泛的功能，包括气候细节的研究、结构分析、与施工人员的会议、数量调查和工艺规划。
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.
Daiwa House Industry Company
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
塑料屋工程始于1959年9月。开发团队由两名工程师组成，包括一名新招募的工程师。试验室建于1960年1月。Sekisui住宅A型于1960年3月建成，4月开始销售。Sekisui House Model B的开发始于1960年7月左右，第一座建筑于1961年6月完工，工程师作为实验的一部分住在里面。B型的销售从七月开始
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
Matsushita Type One是由一个4人团队开发的，该团队由一位以建筑师为职业的工程师领导。发展计划在1959年11月展示，第一座测试大楼在1960年3月完成。试验建筑每年建造5次，这位工程师的兄弟的一家铸铁厂经常为其提供帮助。三个内部部门参与了该项目的竞争
Misawa Homes Company
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
Asahi Chemical Industry Company
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 panel was 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
Toyota Home Company
The department for new business was established in the planning office around October 1967. Four engineers started to study housing in 1969. A half‐scale 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
Sekisui Chemical Company
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
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).
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, 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 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.)
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. 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).
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 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) 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; 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 .
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.
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.
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.
积水 M1型号(1970)采用800毫米模块(2400毫米×5600毫米)。积水 M3模型(1975)将其内部尺寸改为用于8个榻榻米房间的900毫米模块。
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.
大和房型A模型采用了1260毫米的模块，因为该模块中常见的是4 shaku×8 shaku (1 shaku = 30.3 cm)的通用分布式建筑材料，在更宽的跨度中减少钢材的用量可以降低成本;3个模块，代表3780毫米，等于12个shaku(两个ken)，这与榻榻米房间的尺寸一致，在日本住宅中很常见。大和房舍B型(1967年)改型为940毫米模块，以适应小型场地。这个940毫米模块等于两个910毫米面板长度的一半加上一个60毫米宽度的连接器。表3总结了在目标预制房屋中看到的模块及其使用原因。
|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)
|Sekisui House Model B||
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)
|Sekisui Heim M1||
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)
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. An engineer of Sekisui House who was involved in the development mentions the reason they could respond individually using irregular 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. 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. In the development of the rigid frame 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. 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.
Spring lock washer. (Diagrams were extracted from the noninflammable assembling house qualification documents (1962) for Matsushita Type‐one, by the Housing Loan Corporation.)
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.
Left: Eidai House Type‐One Study Hut N33), Right: Gas bath hut. (Extracted from “Creating the housing culture6 (1990),” p. 38.)
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”. It seems that those products, which had limited use, could support the operations of the early unstable prefabricated housing manufacturers.
积水为没有内浴室的公共住房单元开发了一种燃气浴室小屋，并由大阪燃气公司销售(1961年4月，图6，右)。它可以在5小时内建成，总造价为6万日元。标准的建筑面积是900毫米乘1800毫米，并可以增加一个更衣室。Sekisui House每个月收到300到500个gas bath hut订单，这是为了弥补Sekisui House型号A.6的销售疲软.Eidai房子类型一,研究小屋是顺利的,开发的负责人说,在财政年度结束时,可以看到它从工厂运输研究小屋的发售。这些产品的用途有限，但似乎可以支持早期不稳定的预制房屋制造商的运营。
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.
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.
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.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.
The authors express special thanks to the funding source by JSPS KAKENHI grant number 22656128 and all interviewees and those who supported this research.
The authors have no conflict of interest to declare.