One of the most important differences between the on-site subtrade or contractor and the off-site manufacturer is the need for consistent purchase orders with similar characteristics; A constant portfolio (often referred to as a pipeline) is required to cover important investments in everything from marketing to tooling, all essential for high quality and quantity fabrication.
On-site contractors benefit from logistics that are defined and managed according to a single project. Specifically in a conventional design-bid-build process contractors estimate and then purchase all specified elements to build a building and their risk is limited to these purchases. Risk is also mitigated by the fact that any cost overruns that are incurred because of omissions or unforeseen conditions will, in the end, be assumed by the client.
Along with all the same functional, technical and economic criteria of an onsite project, off-site fabricators need to amortize costs over repeated productions. This creates conditions that constantly challenge the economics of high-value-added prefabrication. The bipolar objective of responding to a client’s one-off prototype criteria while managing large overhead costs of manufacturing is completely foreign to onsite builders and thus defines the lack of competitiveness of offsite versus onsite at least when it comes to delivery of one-off projects.
Offsite manufacturing can only be economically feasible if project pipelines permit advanced planning and resource management to justify just-in-time flows that balance sales with bulk purchases. When comparing the bidders' supply chain between two competing companies, one onsite and one offsite, the overhead required to sustain the prefabricator’s advantages, compared with the jobsite contractor who assumes lower overhead linked to project specific tools and materials, is difficult to overcome. Further, materials for the onsite contractor are paid for as claims progress on site.
Unstable demand that does not sufficiently replicate certain elements will never be a viable avenue for off-site construction, if the objective is to reduce costs. The crux of the problem is that ingrained architectural singularity occludes the potential for large-scale project pipelines - this simple but hard to crack polarity has spelled the end for many promising prefab experiments.
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| Similar characteristics in manufacturing of modular volumetric |
