Japanese prefabrication housing construction

As stated by CIRIA Special Publication 139, Japanese house building market is substantially larger than that of the UK and new build housing output in Japan has varied between 4.5 to 8 times larger than in the UK.

Japanese traditional timber housing was constructed using post-and-beam timber frame methods. Modernism then had started in Meiji Period (1868-1912) which gave flexibility to internal layouts and allowed occupants to perceive internal dimension and horizontal spaces from any position within their houses in a more fluid manner than in Western Style dwellings.

For its timber-frame dwellings, Japanese has used a method of 'Precut' which consists of timber structural ridig frames, with members cut to size and finished with complex connections in factories that based on traditional jointing methods.

The principal assumption of an off-site construction/mass production is that reduction in the variety of components used in a system will allow economies in the production of components. The unit cost is reduced by mass production, on assembly lines, where fixed costs (e.g. investment in factory plant) are spread over an increasing number of identical components. Variable costs (e.g. cost of material) are roughly constant per unit, although there may also be benefits because of large volume purchase (CIRIA, 1996).

Modular construction aims to achieve a predictable and efficient construction with excellent quality as promised. It is hoped to give a lower whole life cost, better working environment in the factory, and to achieve a minimum on-site time.

Nevertheless, downside might occur when an off-site construction is in need of larger capacity transport vehicle than in-situ constructed project. Cost also can be appear to be higher than anticipated due to craneage limitation.

So, how sustainable a modular construction can be?