Some owners disagree with the statement that offsite construction is faster than traditional construction. The delays maybe explained by trying to integrate what is a manufacturing process into a linear construction culture. Additional time is required for pre construction, ordering of long lead items, design coordination prior to fabrication, interfacing offsite components with the site and additional transportation time. The other area for consideration is how the business process impact the project especially as it relates to design freezes, when the final cost is fully understood and time to appropriately contract the work. The biggest variable when comparing offsite options is the factory throughput, each supplier is different.
So where can schedule savings be found? Schedule savings are applicable to different approaches like roof trusses, MEP racks, Structured Insulated Panels (SIP), mass timber floors, and bathroom pods as it is with volumetric and modular solutions. The decrease in speed is attributed to the assembly of materials by labour in a different location than the building site, removing the dependency on the previous trade. The work can be installed at site faster due to the prefabrication work opposed to at the site, reducing the compound inefficiency of stacking trades in the same space. Shahzad, Mbachu and Domingo (2015) studied several traditional and offsite projects in New Zealand and concluded the time was reduced by 34% through construction offsite.
Construction is the only industry I can think of where a temporary organization (the project) is created with a new set of people to solve a problem on a different site and in some cases a new municipality. Even in situations of high repeatability there is a new context, stakeholder or supplier that introduces risk. This new entity is disbanded at the end of the project and the everyone moves to the next project. Is it any wonder that schedules slip when some element of the project is the first time every time? Repeatability should drive schedule reductions even further.
Even with the longer preconstruction requirement the overall construction schedule should still be faster with offsite approaches than conventional construction. A collaborative approach will facilitate the outcome.
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