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.

With the labour cost contribution of 30%-50% to the total construction cost of a typical building, construction is recognized as a labour-intensive industry. The extant literature evidenced that there exists labour scarcity in many construction trades, which has caused several negative effects. Hence, the assessment of labour requirements prior to the commencement of the building construction would help to mitigate the effects due to labour shortages at the organization and project level. This research aimed to assess the labour requirements for the cost significant trades of two-storey houses in Sri Lanka. The study involved a survey of thirty-eight (38) two-storey houses to collect the required data. The required data were extracted from the Bill of Quantities (BoQs) of those 38 buildings and assessed based on the norms available in the building schedule of rates (BSRs) practised by the key construction companies. The analysis identified that the finishes, in situ concrete works, doors and windows, services, masonry works, and roof works are the significant trades, respectively in the descending order of their contribution to the total cost. However, in the descending order of their labour requirements, finishing works, masonry works, concrete works, reinforcement, formwork and roofing work are more labour-based activities, require 0.274 skilled labour days and 0.228 unskilled labour days, on average for the construction of per unit (sq.ft) of gross floor area (GFA) of a two-storey house in Sri Lanka. Further, in the case of two-storey houses, cost significant trades contribute to around 19% of its total cost. This would enable estimating the labour cost for a proposed project and thereby implement appropriate strategies to manage the labour shortages in projects and the construction industry as a whole.