The distinguishing characteristic of the design–build, or design–construct, method is that the owner executes a single contract with an organisation that becomes responsible for both the design and the construction of the project. This approach closely resembles the ‘master builder’ whose tradition goes back to Biblical times (Tenah, 2001). If you needed a project built, you needed only to contact a single expert, a master builder, whose expertise, experience and contacts would assure a successfully completed project. In their Construction 21: Reinventing Construction report, the Ministry of Manpower and Ministry of National Development of Singapore (1999) note that one of the primary reasons for low productivity in the construction industry is the lack of integration of activities across the project life cycle. Indeed the traditional design–tender–build approach described above, with its organisational separation of design and construction, has great potential for such lack of integration. Construction 21: Reinventing Construction urges that the design–build method, and others, be implemented as a means of improving productivity.
The Design–Build Institute of America (1994) lists potential benefits from the design–build method as follows.
Singular responsibility. There is a single point of responsibility for quality, cost and schedule adherence, avoiding ‘buck passing’ and ‘finger pointing’.
Quality. The greater responsibility implicit in this method provides motivation for highquality and proper performance.
Cost savings. The single entity with whom the owner contracts can work together as a team to evaluate alternative methods and materials efficiently and accurately.
Time savings. Design and construction can be overlapped, and bidding time after design is eliminated, thus offering the possibility of substantially reduced project duration.
Potential for reduced administrative burden. After the contract is agreed upon, the owner will have relatively little investment in coordinating and arbitrating between designer and contractor, since they are a single entity.
Early knowledge of firm costs. The single design–construction entity is responsible for both design and cost estimates at an early stage, thus allowing early establishment of financing and reduced exposure to cost escalation.
Risk management. Cost, schedule and quality can be clearly defined and appropriately balanced. The design–build organisation will manage many of the risks that the owner might otherwise be responsible for.
Balanced award criteria. The owner can give credit in the award process for such considerations as design quality, functional efficiency and team experience, as well as lowest first cost.
To be fair, one should also recognise some disadvantages of the design–build method. These include the following.
Importance of the project brief. Without a clear statement defining the owner’s needs, the design–build organisation cannot understand the required scope prior to contracting with the owner.
Difficulty of establishing a price for the work. It is difficult to establish a price for the work until the design is complete, which it is not when the design–build organisation is selected.
Costly tendering. Owners must expect to pay for the efforts by design–build organisations to assemble their tenders. These efforts often include preliminary design work, necessary to determine prices.
Short tender periods. Design professionals often are subjected to inordinate pressure to complete their tenders, including any necessary preliminary design, in a few weeks.
Potential low quality. Oversight of the on-site construction activities is left to the owner.
Because both designer and contractor are one organisation, the designer cannot fairly represent the owner on site.
Less control over subcontractor and consultant selection. The owner is farther away, contractually, from the process of engaging subcontractors and subconsultants, whereas in the traditional design–tender–build process often the owner has the role of approving nominated subs.
Generally less control by the owner over both project definition and execution than design– tender–build projects.
A study of design–build projects in Hong Kong found that the proportion of public sector contracts of the design–build type increased from 0.9% to 9.9% between 1992 and 1999. The report lists single-point responsibility, sole liability, better project management, better time control and better cost control as potential advantages of this method. It also notes that limitations include design and quality management, restricted variations, heavy client burden and lack of experienced design–build firms (Chan et al., 2001).
In Figure 2.2, we show a simplified relationship chart for a design–build project. Note that the owner has a contractual relationship with a single organisation that is responsible for both design and construction. This organisation, in turn, engages subconsultants and subcontractors to assist with design and construction.
The Singapore Construction 21: Reinventing Construction report (Ministry of Manpower and Ministry of National Development of Singapore, 1999) cites an example of time savings with the design–build method, as follows:
Millenia Tower (42 floors) and Centennial Tower (37 floors) were both constructed by Dragages Et Travaux Publics (Singapore) Pte Ltd. Both buildings were built 2 years apart, and have a floor area of about 2,000 m2 each. Millenia Tower was initially designed by the owner’s team but modified by the contractor, whereas Centennial Tower was a D&B project (by the private sector). Millenia Tower was built in 32 months with 6 days per floor for the structure, whereas Centennial was built in only 23 months with 4 days per floor for the structure, 30% faster.