Understanding performance limits in off-site structural frame construction

Off-site construction is promoted as a means of improving productivity in the construction industry. Its standardised production processes create a favourable environment for applying lean principles. However, evidence suggests it does not always result in faster construction. We investigate the reasons by analysing the superstructure work package of a 14-storey residential building in London, using installation data for 2,070 precast columns, twin-wall cores, and lattice slab components. Construction speed, measured as the production rate (m² of floor area per day), showed a significant linear relationship with installation variability. Variability arose from factories producing similar components in batches for multiple projects, delays in issuing designs to factories, and out-of-sequence deliveries to sites with limited storage capacity. Handovers between off-site and on-site activities also exhibited greater variability than purely on-site handovers. The findings suggest that, if variability were minimised, construction speed would follow an inverse U-shaped trend, with initial improvements due to workers’ learning effects, followed by subsequent reductions associated with longer transportation distances for pre-manufactured components at higher levels. This study quantifies the variability-performance relationship in off-site construction and identifies the interface variability gradient between off-site and on-site handovers.