Off-site construction is often suggested as being able to bring about several benefits to the construction process such as improving productivity perfor- mance and improving the quality of built facilities in a cost-effective man- ner; studies and reports from the United States, Australia and the United Kingdom indicate off-site construction gains; however, evaluations of off- site construction may be somewhat too grounded in anecdotal evidence rather than rigorous data. There is currently a lack of research that objec- tively measures the benefits of off-site construction. Instead, most research focuses on subjective studies of experiences with off-site construction. A number of factors assess prefabricated benefits:
Time
The most significant benefit of off-site construction is argued to be time-savings. By transferring a significant proportion of the construc- tion work to an off-site facility, time spent on-site is reduced. The more predictable conditions of the factory and the economies of scale generated may ensure that construction deadlines are met more effec- tively than in a traditional on-site environment. In studies, a signifi- cant majority of respondents regularly choose time/speed as the main reason for preferring off-site construction. Time benefits are regularly reported by almost half of any surveyed group of practitioners as the main reasons for using off-site construction. Reductions in on-site assembly time are perhaps one of the main benefits of off-site methods over traditional methods.
Quality improvement
Another benefit, cited by many stakeholders, is quality improvement enabling tighter control than an on-site environment. A perception exists among clients that elements made off-site, in a factory, are more consistent and had gone through a greater degree of quality control and testing than elements made on-site. Less time spent on snagging (remedial works) was also mentioned as a benefit. Previous studies find that quality is the second most significant factor (after time) reported by clients in choosing off-site construction: indeed, a sig- nificant number of study participants (almost one-third of clients and designers responding to request for information) cite quality improve- ment as their first choice, whereas 15% of contractors do the same.
The potential for improvement over time is key and significant given industry’s move towards continuous improvement globally (via Bechtel and other dominant players). There remain opportunities to apply operational management (total quality management) tools/ techniques towards the measurement of current and subsequent improvement of future efficiency in the civil engineering industry.
Relieving skills shortages
A third major factor behind stakeholders favouring off-site construc- tion addresses skill shortages. Off-site construction enables construc- tion processes to be ‘outsourced’ to another environment, requiring less labour to be invested into traditional on-site processes, addressing skill shortages. Indeed, almost two-thirds of house-building firms (in the UK) cite this as a driving force. Compensating for craftsmen skill shortages, remains within the top six reasons for general contractors using off-site construction. Australia, like many other countries, cur- rently recognises skill shortage by active recruitment and apprentice schemes; the extent to which this is more viable in the urban centres and in factory-based environments, rather in rural on-site locations, may be an added factor.
Cost
Of all perceived benefits of off-site construction, cost was the most controversial; some sources citing it as a major advantage but some listing it as a major disadvantage. Improved cost certainty of off- site construction may well be perceived to lessen the likelihood of cost blowouts; however, other studies find that key stakehold- ers did not rate cost as a benefit at all. One study finds that more than 90% of respondents believe higher initial off-site construc- tion costs were an inhibitor to wider use and a significant limi- tation to off-site construction, with another study showing 50% of clients/designers and 40% of contractors and builders listing cost as a main barrier to off-site production uptake (inherently perhaps as a result of the huge knock-on transportation costs that can accrue). These results somewhat fly in the face of other studies that argue that almost half of all clients and designers questioned regularly cite reduced initial cost as an advantage of off-site con- struction; indeed, with 40% of respondents citing reduced whole life cost as an advantage to be gained from off-site prefabrication and modularisation.
Productivity
A broad view indicates that greater productivity can be viewed as the overriding benefit of off-site construction, with the reduced time, higher quality and lower cost of projects ultimately meaning that the process is more productive per unit of input than on-site construction.
Indeed, the future work proposed by this study has, as one of its aims, a structured means and method to identify and measure the variables of productivity objectively.
Disadvantages in off-site construction
There are significant perceived disadvantages to off-site construc- tion among key stakeholders. A (UK) survey of house-building firms finds that only one-third of respondents were satisfied with the per- formance of off-site methods within their own organisations and only half of those who had tried prefabrication were satisfied with the performance of off-site construction generally (as compared with respondent satisfaction levels related to more traditional on-site in
situ construction with a happiness level of more than two-thirds).
On balance, off-site construction is still perceived negatively and is seen as being less effective than on-site construction. The biggest disadvantages for stakeholders were
• The poor build quality of prefabricated components • Incorrect designs
• Delayed delivery time
• The volatile nature of the supply chain • An inability to make changes on-site • Related long lead (lag) times
• ‘Designers’ favour customisation rather than standardisation • Albeit that perhaps the current Western Australian client
need (for component supply/installation of uniform solutions), expressed by mining and resources industry clients, favours standard isation and does not seek architecturally significant solutions.
Regulatory guidance was also a major barrier preventing the full exploitation of off-site construction. There is a perceived lack of guid- ance codes and standards particularly related to off-shore supply chains. Generally, civil engineering and the construction industry are traditionally risk-averse and there is insufficient knowledge of objec- tive benefits of off-site construction beyond perception.
There is somewhat of a lack of an Australian focus in much of the current available literature; insights developed overseas require contextualisation for Australia (and Western Australia). Although investment in off-site con- struction is currently nominal in Western Australia, resources and mining industry clients are in fact increasingly seeking prefabricated solutions.
Extending the theme that case studies help to better assess the relevancy of off-site construction, Section 4.6 explores design specification choices related to precast in lieu of in situ concrete.
4.6 PREFABRICATION AND DESIGN