Comparison of construction cost of residential buildings in Sri Lanka: offsite vs onsite

Abstract

Offsite construction (OSC) entails the planning, designing, manufacturing, transportation, and assembly of prefabricated building components at the construction site. As recommended in previous studies, the offsite construction technique can be considered a high-quality and cost-effective construction method that consumes less time and labour while delivering higher productivity. Consequently, it is recognized as a sustainable solution compared to existing onsite structures in countries like Sri Lanka, given the restriction on the availability of resources and high constructional cost. However, this technique is underutilized in the Sri Lankan construction industry, creating a significant void that must be addressed with sufficient cost data and broader access to knowledge regarding the positive impacts of the technique. This research seeks to evaluate current OSC practices together with a comparison of the cost of two similar-natured onsite and offsite residential projects to determine the economic feasibility of OSC in Sri Lanka. The required cost data were extracted through semi-structured interviews with the professionals who engaged in building projects and document reviews. The comparative analysis indicated that beams, columns, masonry walls, and wall finishes (plastering) are contributing to 100% cost-saving in offsite projects compared to onsite projects due to the offsite concrete wall. Further, concrete walls, stairs and ramps, roofs, and floor slab shows 25%, 16%, 12%, and 8% cost saving for the off-site project compared to an onsite project, respectively. Hence, the adoption of off-site elements would enable construction clients and investors to achieve substantial savings in the construction cost of buildings.