The pro prefab MEDIC

roponents of off-site prefabrication have no doubts about its ability to improve the performance of the construction industry. They claim it increases the quality and reduces uncertainty and overall costs of a project.

It is also claimed to reduce and simplify maintenance and to extend lifespans while reducing life cycle costs.

However, little data has been available to support these claims in a form that is acceptable to designers and specifiers industry-wide. The Modular Engineering Design Integrated Construction (MEDIC) project aims to redress this omission.

MEDIC was started "to assist in design decisions to take advantage of the off-site manufacture of building services distribution". The main tasks of the project are to collect and disseminate information on prefabrication design and installation methods, on-site erection times and resources and those of traditional build equivalents. Once processed, these details will be published on the MEDIC web site.

A number of companies other than the main participants [see box] have already made practical contributions to the project, and last November a seminar on work undertaken so far was held with the aim of attracting more collaborators.

The meeting unveiled the results of the first trial studies, carried out on the Stansted Airport terminal extension, and the information available on the MEDIC web site was explained to seminar delegates.

Central to the prefabrication debate were details of the work undertaken by a Nottingham University team to identify factors that designers, contractors and clients consider decisive in opting for off-site assembly of building services modules.

Prefabricate advantages "Reduction in on-site operatives, higher productivity, and an increase in site and factory efficiency," were cited as advantages of off-site prefabrication by Gary Connolly, operations manager at Crown House Engineering's Wolverhampton facility.

At the November seminar Connolly presented the case for plantroom manufacture. "These advantages arise from a commitment to innovation, which is an integral part of the approach to off-site prefabrication," he stated.

"Off-site prefabrication is a way towards building successful relationships and focusing on procurement and customer requirements," he added. The method enables pre-testing to be carried out prior to delivery, thus reducing the risk of things going wrong and so improving the handover to customer. Yet another benefit is that maintenance can be built into the design.

Collectively, the benefits quoted by Connolly can lead to reduced life cycle costs and project time, faster installation, and improved quality – among the most common factors affecting the decision to use off-site prefabrication according to the Nottingham University MEDIC research team headed by Dr Mick Mawdesley.

For its study the team reviewed existing reports, carried out structured interviews with professional groups outside the MEDIC steering group, alongside detailed discussions with steering group members. It identified 22 factors, of which money, cost, time, safety, quality, service to the client, building life expectancy, and uncertainty were the most common. Very little agreement was found, however, amongst the different groups in a construction project – clients, designers, contractors and consultants.

Clients rate money and cost as the most important factors, with quality and building efficiency as second and third most important. Consultants place time most important, before money and productivity.

Reduction in installation time is considered by contractors as the most important factor, with money second and time in third place. Designers placed time highest, followed by quality and reduction in installation time.

Of course time means money, and to the contractor they are virtually interchangeable in their effect. For clients, quality and building efficiency can have an effect on costs; hence their placing of these factors as the most important.

The views of suppliers were sought but so few responses were received that they were omitted from the final analysis.

"Information is now needed on if and how architects, procurement routes and cost and value constrain manufacture and vice versa," stated Mawdesley.

In seminar workshops, delegates stated that more publicity is required on the benefits of prefabrication. They also showed strong feelings for a real need for partnering, and importantly, they emphasised the need for there to be mutual trust between the different parties to a construction project.

Trial run for MEDIC The Stansted studies took place in September 2000. These covered the installation of four modules; two of pipework and fittings and two of electrical cabling and ductwork and were completed by BSRIA (the Building Services Research and Information Association).

On average, each module took 2·5 hours to install after delivery on-site. "If the pipework on a mechanical module had been installed conventionally, at BSRIA best practice rates, it would have taken two operatives 24 hours," stated the Association's Glenn Hawkins. The installation of the cable management systems and luminaires would have taken two operatives 11·5 hours.

In other words, the prefabricated modules were installed 9·6 and 4·6 times quicker than if conventional best practice had been followed.

Room for improvement was found however, in the methods used to connect the modules to the structural steelwork. Certain design aspects of module components and fixing devices could also have been improved says BSRIA. And, with the electrical modules, a large amount of on-site cable installation was still required – ways of overcoming this need to be identified.

With the mechanical services modules, pipework was excellent, Hawkins reported. He praised the jointing processes using mechanical couplings, press fittings and flanges as "simple and effective". It was recommended that a sufficient length of uninsulated pipe should be left at each end of the module to receive the coupling, but this was an issue on only one length of pipework.

While overall installation of the modules was fast, the project was delayed by three days due to inadequate pre-planning for the scaffolding erected to support the modules during installation – this was still being erected when module installation was due to start, and once up it could not be used until calculations confirming its load-bearing capacity had been received.

BSRIA stresses the need for a single point of responsibility to determine how modules are handled on-site, and the requirement for a thorough evaluation of the load-bearing capacities of both permanent and temporary structures.

The Association was critical too of the storage of structural and scaffolding materials at the base of the scaffold platform. Hawkins and his team say this presented a safety hazard to personnel guiding modules from ground level while they were being hoisted into position by crane. It also interfered with the installation of the modules.

Materials storage, recommends BSRIA, should, like all site activities, be strictly coordinated.