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Market share

Standardisation and prefabrication are not new concepts. Both techniques have been used increasingly in construction as a means of improving quality and increasing efficiency. Despite this trend, however, there are still many projects that fail to benefit because neither the client nor the design team considers the techniques at an early stage.

The first uses of prefabricated bathroom or individual toilet modules or pods in the UK are probably in the Lloyds building in the City of London and the Broadgate Office Development near Liverpool Street Station. Using techniques developed in the States to manufacture completely fitted-out and serviced building blocks ready to plug into the main frame, the specialist sector of prefabricated toilet and bathroom pods has gradually evolved.

Preassembly or prefabrication is not appropriate across the whole of the industry, or for all elements of a particular development or project. The nature and scope of the work will dictate whether prefabrication is useful. Prefabrication requires more time and effort to be applied at the beginning of a project but can ensure higher quality standards are delivered with reduced on-site construction time.

The main benefits from prefabrication are:

• enhanced quality
• lower on-site assembly and installation costs
• increased installation efficiency and speed
• improved predictability 鈥� clash detection and buildability
• increased social and environmental benefits (safe and healthier working environment through less site work)
• ease of maintenance and replacement, as systems are pre-engineered, which allows for ease of replacement.

There are no published statistics as to the extent of the prefabricated market. However, a survey of large new-build commercial office projects (more than 100,000 ft2) that Gardiner & Theobald has been involved with over the past five years reported that 20-30% of such schemes are using prefabricated toilet modules.

The use of bathroom and toilet pods has been the success story for prefabrication in the UK industry, where high volume repetition in hotels and student accommodation has seen economic advances. This is now gathering momentum as off-site manufacture is being championed as the solution for the procurement of all large volume construction outputs in the education, health and housing sectors of the UK industry.

The project team should systematically examine the opportunities for introducing prefabrication into a project in the very early stages (inception, concept design and scheme design). Once scheme designs have been completed, there is limited value added in investigating options for prefabrication, it is more likely to cause disruption to designs already agreed upon and could ultimately delay the project.

According to PrOSPa, a Loughborough University programme funded by the DTI to promote off-site production, the uptake of prefabrication technologies has been disappointing, and is restricted to a small part of the industry (such as toilet fit-out service modules and hotel bathroom suites), and is far below the levels required to optimise the benefits to the sector and to the built environment as a whole.

However, the industry can expect growth in off-site technology, with more contractors entering the market and clients and developers increasingly opting for prefabricated components as a way to ensure cost-effective purchasing and quality assured materials.

As recently detailed in 黑洞社区 Offsite Directory 2005, in the 1990s it was private sector businesses such as fast food chain McDonald鈥檚 and airport operator BAA that embraced and chaperoned offsite techniques. Now, their lead is being followed by the public sector, such as NHS trusts and housing associations, with the London 2012 Olympics likely to mark the next phase of the evolution of prefabrication.

Procurement

Because of the volume of production work involved, any off-site fabrication involves booking slots of time within the manufacturing facility. This means that lead times tend to be significant as large volume production ties up resources. Lead times of 20 weeks for a toilet pod are not uncommon, with an average of eight to 12 weeks normally required before off-site manufacture can commence, as shown in the chart.

Once a prefabrication decision has been made it is advisable to involve the specialist contractor early in the process and make an initial formal appointment detailing the requirement for preconstruction advice and technical input during the design development.

Achieving an agreed design freeze is paramount to the successful delivery programme.

The prefabrication of volumetric toilet pods involves the manufacture and assembly of the complete unit, which is fully fitted out before it is placed in final position. As such, it brings together the full spectrum of internal fitting out trades such as drylining, joinery, electrical, mechanical, ceiling fixing and high quality finishing trades including tiling and stone masonry. It is not uncommon to have 12 separate trades working off site under the specialist fit-out contractor鈥檚 control 鈥� hence the need to choose a competent, experienced specialist with appropriate management and quality control procedures in place.

The procurement programme required for the prefabrication assembly is therefore detailed and complex and mirrors the operations that would traditionally be planned as on-site activities. The specialist effectively becomes a E E main contractor for the off-site manufacture.

Once production commences the key to efficient fabrication is manufacturing standardisation and repetition. Where off-site manufacture has fallen down in the past is through the high incidence of one-off component use, with at least half being used only once and the remaining repeatedly used only between two and six times on average.

Clearly there is an optimum point where cost and delivery programme are balanced, dependent upon the particular project details. However, a minimum manufacturing time off-site is always required to deliver the product with sufficient quality and buildability.

Overall total efficiencies to installation programme are delivered by the reduced site installation times. Again this is difficult to quantify and is dependant upon the project specifics, but savings of 10-20% of on-site programme are achievable on overall delivery. This can equate to major cost savings for the project when translated to commensurate site preliminaries and organisation costs.

 

Typical costs

The production of volumetric toilet pods will normally add about 10% to the cost of traditional on-site bespoke production. The premium covers the following additional costs:

• initial design and feasibility studies
• mock-ups
• fabrication of modular enclosures
• additional cranage and logistics for positioning modules

This cost premium needs to be balanced against the savings of on-site activities through the reduced site programme.

Typical rates that can be expected for toilet modules are dependant on the quality of material and finish specified and volume repetition. (See graph below for illustration of typical rates.)

Key issues to be considered in the costing include where the costs and responsibility for design will fall, and the extent of site works required. The development of the design for the fit-out elements, up to a detailed working drawing level, has to be paid for through the specialist contractor. It is easy to forget in any off-site solution that management, temporary works and logistics are still required for the site element of works once the completed pod has been purchased.

Surveyors should also make sufficient budget provision to reflect the cost of an off-site mock-up and samples, with allowance for some design development to these at the manufacturing works. It is usual practice for the off-site mock-up to become the agreed benchmark for the quality and workmanship standards, with the mock-up being retained off site and not incorporated into the site works. This allows the team to refer back to the benchmark or test out any changes at the off-site facility without disrupting site works. All costs associated with its production are therefore normally sacrificial but ultimately drive the value-added benefits of prefabrication.

The successful procurement string will have a team fully integrated with the client design, specialist and the main contractor all acting together. The programme should be very disciplined in reaching sign-off and approval prior to manufacture, as any late changes will be extremely costly. Rather like design-and- build procurement, unpicking or revisiting off-site manufactured products will involve the reallocation of resources of each party, leading to high overhead costs. Surveyors should be aware that even a relatively small change to detailing could have major cost implications and can represent poor value to the finished product once a design has been fixed.

The fabrication of highly serviced areas in off-site factory conditions obviously requires a production facility with a level of sophistication and capacity to deal with the intensity of work required. The overheads and running costs for such a production facility will have to be ultimately fed back into the selling price of the finished works, which, together with design, can appear disproportionately high.

 

Future developments

The government is continuing to push the merits of off-site construction, and the National Audit Office鈥檚 report on cost and programme of modular construction has kept the topic firmly on the agenda. Although the NAO report may not directly recommend the expended use of prefabrication bathroom pods and the like, its implications on the efficient use of prefabrication will highlight an important issue for those hoping to improve productivity.

Given the intense use of labour in off-site production, there is strong competition from specialist manufactures in low-wage economies such as Eastern Europe. Similarly to what has happened in the furniture market, the UK prefabricated fit-out market is under pressure from high-quality manufacturers who can undercut supply costs because of cheap labour. As quality is driven up through repetition with cost being similarly driven down, the larger the order the greater the commercial advantage that can be realised from an efficient low-cost supplier.

The emphasis on whole-life costing for prefabrication is becoming more of an issue in the choice of procurement route. The off-site construction in factory conditions should lead to inherently better quality with fewer defects and therefore lower lifetime costing. Detailing of areas such as thermal performance and air leakage are considered in much greater depth and installed to better standards as a bespoke solution off site, rather than what could typically be called a 鈥渞epair鈥� on site.

Pre-engineered solutions should also generate much better environmental performance through the reduction of waste as materials go through the factory assembly process with efficient scheduling, cutting lists, careful handling and storage during production.

The reduction of site installation time is also considered a sustainable benefit because of the reduction of site logistics, transportation (of both workers and materials) and environmental noise pollution of physical installation.

Does this mean every new building will have a standard service module for WCs and bathrooms in future? Probably not, due to the desire for discernable bespoke products, but the incidence of prefabrication offsite will continue to increase and improve construction efficiency.