London mayor urged to get behind off-site housing manufacture

So-called off-site manufactured (OSM) housing has failed to take off due to the lack of mass market demand and the lack of a single design standard, according to a new report by the London Assembly's Planning Committee (65-page / 1MB PDF). It has urged mayor Sadiq Khan to develop and adopt a London-specific OSM design code, and to provide "clear and strong leadership" to encourage adoption of this type of housing.

The much-maligned 'prefabricated' housing of the post-war period contributed significantly to housing need at the time, with over 425,000 homes, many of which were substantially manufactured in factories, built in 1968, according to report author Nicky Gavron. The precision-manufactured, high quality factory-built models of today are "unrecognisable" from the prefabs of the past, she said.

"Meeting London's housebuilding target is a huge task, and traditional construction techniques will only take us so far," she said. "OSM is an innovative, forward-looking and exciting way to close the gap. These buildings are high quality and outstanding in terms of performance. Their construction is more environmentally-friendly than traditional construction methods and they are a far cry from their prefabricated predecessors."

"The lack of a single design standard or mass market demand has held back the sector's growth. This is a once in a generation opportunity to work collaboratively with investors, developers and policymakers at a time where experts, central and local government are all calling for the same thing to happen. The mayor is ideally placed to respond to the report's recommendations and call to action," she said.

The term OSM is used to refer to housebuilding based on individual components that are manufactured in a factory, transported to the site and then mostly, or entirely, assembled on location. Constructing the components in a factory allows for quality control and, once delivered, the components can usually be assembled at the site in a matter of days or weeks, according to the report.

OSM homes currently on the market can meet the needs of families with children, older people and single households, and the business model is particularly suitable for delivering new rental accommodation cheaply and quickly, according to the report. Their shallow foundations, lightweight construction and high acoustic and thermal insulation standards also make them ideal for constrained sites, and transporting materials to the site can be done with far fewer vehicles, so reducing the impact of congestion.

To deliver these benefits, the report recommended that the mayor take the lead on developing a London-specific design code for OSM, "building on emerging government construction strategy thinking in the UK and also what is currently being developed in Australia". The code, which should be developed in conjunction with designers, manufacturers and housing providers, should act as a mayoral 'kite mark' and be backed by suitable warranty providers to promote its use, according to the report.

The report also recommended that the mayor look into using some of the 5,700 acres of London land owned by Transport for London (TfL) to support the delivery of OSM housing. Much of this land, on which TfL is already planning to deliver 10,000 homes, consists of small and constrained sites, making OSM an ideal housing solution. The mayor should also focus specific funding on the OSM sector and set up an OSM-led procurement framework, according to the report.

Gavron acknowledged that there was an "understandable degree of nervousness" around the use of OSM, as it required different funding and delivery models and a different way of doing business. However, the mayor was in an "ideal place" to lead a change in attitudes, she said in the report.

London needs 50,000 new homes a year to meet its growing needs, Khan said last year in his mayoral manifesto.