Construction Constructability analysis

In our discussion of planning and feasibility studies, we mentioned the use of constructability analyses and studies as a means of making the construction process more efficient. It is important that this attitude be present throughout the planning and design phase. The presence of a construction expert, perhaps by virtue of the early engagement of a construction manager, can greatly assist this process. Constructability has been defined as ‘the extent to which a design of a facility provides for ease of construction yet meets the overall requirements of the facility’ (Wideman, 2001). Continuous constructability studies throughout the planning and design phase can help to anticipate potential problems involving material compatibility, access issues, sequencing problems, dewatering, weather or delivery issues, unnecessary complexity, new or proprietary installation methods and long-term performance. A study by the US Federal Transit Administration (2001) of a bus maintenance facility, rail station and parking area project revealed the following actual problems that could have been identified by an early constructability analysis.

 The site geometry of the bus maintenance facility was conveyed inaccurately on the contract drawings, impacting quantities of sitework and utilities.
 Sprinkler design was not adequately presented to comply with local codes.
 Electrical requirements for owner-supplied equipment were not conveyed on the drawings.
 Lack of coordination between plumbing and architectural drawings resulted in numerous inconsistencies.
 Fire protection and fire alarm systems did not meet with local codes.
 Conflicts between light pole foundations and large diameter pipes comprising the underground detention basins under the parking lots necessitated redesign.

A term closely related to constructability analysis is value engineering, value analysis or value management. One definition (Fisk, 2003) is ‘a systematic evaluation of a project design to obtain the most value for every dollar [or other denomination!] of cost’. Some construction contract documents provide incentives for the contractor to suggest ‘value engineering changes’ to the design after the construction contract has been signed, with arrangements for sharing of any cost savings. The practice of value engineering has crept backwards in the project life cycle and is now a regular part of the planning and design phase, even before the engagement of the contractor. The Public Buildings Service of the US General Services Administration generally contracts with an independent consultant to conduct two value engineering studies, the first at the completion of schematic design and the second at the end of design development (General Services Administration Architecture and Construction, 2000).

The Society of American Value Engineers defines a five-phase process for such studies incorporating information, creative, judgment, evaluation and development phases. Under this approach, a study of a US$ 75 million water pipeline project in California, USA resulted in a US$ 5.5 million saving; the saving was reported to be over 68 times the cost of the study. Among the most significant design modifications were the realignment of a roadway to minimise utility relocation and the use of rip rap in lieu of added depth at stream crossings (Johnson et al., 1998). The distinction between constructability analysis and value engineering, if any, is that while both practices focus on quality and costs, constructability includes more emphasis on safety and scheduling; also, constructability tends to involve collaboration of designers and constructors from the outset of the project life cycle (Dorsey, 1997).