A study of key design decisions at the scheme design stage of building projects in Hong Kong Sar with a view to buildability enhancement

Every building project will go through a series of stages in its design development. An important stage is the Scheme (or Schematic) Design Stage. The RIBA in the UK defines the purpose of this stage as "to complete the brief and decide on particular proposals, including planning arrangement, appearance, constructional method, outline specification and cost and to obtain all approvals". An elaboration by the AIA in the US shows that the tasks in the Schematic Design Stage consist of the preparation of drawings and other documents illustrating the scale and relationships of the project components for approval by the owner. This is a significant step to meeting the objectives of the project. After approval by owners, design development will proceed to produce detail design drawings. Hence, the Scheme Design Stage is critical for buildability improvement to achieve higher productivity at the construction stage, since changes after this stage would be difficult without incurring additional time and cost. Therefore, an investigation was carried out to identify the key design decisions which are frequently made at the Scheme Design Stage, on which buildability assessment can be focused. A buildable design would improve sustainability of building development in that savings can be made in the use of increasingly scarce construction resources. Through a questionnaire survey both in the public (including housing and non-housing) and the private sector, a set of 35 design decisions have been identified as being frequently made by the design team, out of over 90 design decisions made at all stages of design development. Further analysis using the Mann-Whitney non-parametric test also reveals interesting comparisons between the public housing, public non-housing and private sectors. These findings have been validated in a series of subsequent interviews with design team members in the sectors concerned. The results of this study pave the way for a buildability assessment model for use at the Scheme Design Stage of building projects in Hong Kong SAR, where productivity needs improvement to mitigate the impact of high land cost on property development.