Mass customization (MC) refers to the ability to provide (i) personalized goods and services with (ii) efficiencies similar to mass produced or standard products. These two seemingly conflicting goals are closely connected to (i) value (concerned with fulfilling clients’ requirements) and (ii) flow (concerned with minimizing waste in processes). Although MC has been mainly implemented in the manufacturing sector, a number of research initiatives have examined its application in construction. We present here the Customization ‘House’ (a praise to the Toyota Production System ‘House’): a roadmap for those seeking to provide bespoke and thus value-added units in repetitive projects (houses in an allotment, offices or apartments in a building, etc.) without compromising flow.

Scope of Customization: the foundations

The foundation of any customization strategy is to clearly define what can and what cannot be customized. This can be done by outlining the available options for each customizable attribute (for example, three flooring options for the living room, two layout options for the apartment interior, etc.) using design drawings and specifications lists and images. The combinations among these attributes and the resulting number of product variants should also be elicited. In the example above mentioned, there will be six product variants if all layout options can be combined with all flooring options. In some instances (when customization is not limited to a few attributes), it is more reasonable to outline the elements that cannot be customized (for example, external walls, windows, shafts, structural elements, etc.). This also requires design drawings to clearly highlight the elements that cannot be altered and where they sit in the project design. Although apparently simple (and perhaps obvious!), failing to outline the scope of customization in detail leads to structural problems in the House’s pillars, slab and roof.

Information and Production Flows: the pillars

The Information Flow starts once the company sends documents (design drawings and/or a menu with options for clients to choose from) and ends after clients’ decision regarding the desired customization is processed and readily available for production (usually in the form of design drawings used by crews on site). This provides the starting point for the Production Flow, which ends when a bespoke unit is completed. It is important to outline the steps involved in the Information Flow and their durations (including eventual loops) and its total lead time. The Production Flow should be used for mapping the key construction stages using the long-term plan for completing the units and for detecting when information regarding the desired customized is first needed. This is called the Decoupling Point (DP) and is the first moment in time in which construction can be disrupted due to customization. Such disruptions can arise from two sources: (i) variability in receiving client input (namely, when a client’s decision will be available) and (ii) variability (or variety) of the product/unit. Further details on how to map the Information Flow and its connection with production as well as practical examples can be found in Kemmer et al. (2010) and da Rocha et al. (2016).

Product Design: the slab

Building the foundations and the pillars create a solid basis for minimizing disruptions in flow. This is achieved by increasing the awareness of the customization boundaries and re-organizing processes (Information and Production Flows) to suit the defined scope of customization. The slab provides the next stage in this journey, but differently from previous house parts, entails a radical change in the design of the product and the production system. The first step is to identify all product parts that do not change across product variants and group them as a stand-alone platform. For example, if two layout options for an apartment entails either an extra bedroom or an enlarged living room (by eliminating this bedroom and incorporating its area into the living room), other spaces in the units such as kitchen, laundry, bathroom, other bedrooms, etc. can be designed as a platform that can be independently and fully constructed regardless the two options to be added to it.

The second step is to design each option as a module, namely, as a part that can be seamlessly attached to the platform. This requires the enclosure walls, doors, service systems, and other components of the platform interfacing potential modules to accommodate any of the modules. The last step is to reflect such design rationale in the production system to enable a portion of the production flow to be completely shielded from customization disruptions. This is achieved by maximizing the platform size and constructing such elements first, thus postponing the DP and the modules production (an approach known as Delayed Product Differentiation – DPD). Simulation results for a real-world project show that an increase from 0 to 30% of the production time shielded from customization disruptions can be achieved by adopting DPD (da Rocha and Kemmer 2013). Practical and detailed examples of platforms and modules for both off-site and traditionally built projects can be found in Gravina da Rocha et al. (2019), da Rocha and Kemmer (2018), and Rocha and Koskela (2020).

References

Gravina da Rocha, C., El Ghoz, H. B. C., and Jr Guadanhim, S. (2019). “A model for implementing product modularity in buildings design.” Engineering, Construction and Architectural Management, 27(3), 680–699.

Kemmer, S. L., Rocha, C. G., Meneses, L. O., Pacheco, A. V. L., and Formoso, C. T. (2010). “Application of Lean Principles to Manage a Customisation Process.” 18th Annual Conference of the International Group for Lean Construction, K. Walsh and T. Alves, eds., Haifa, Israel, 306–315.

da Rocha, C. G., and Kemmer, S. (2018). “Integrating product and process design in construction.” Construction Management and Economics, 36(9), 535–543.

da Rocha, C. G., and Kemmer, S. L. (2013). “Method to Implement Delayed Product Differentiation in Construction of High-Rise Apartment Building Projects.” Journal of Construction Engineering and Management, 139(10), 05013001.

da Rocha, C. G., Kemmer, S. L., and Meneses, L. (2016). “Managing Customization Strategies to Reduce Workflow Variations in House Building Projects.” Journal of Construction Engineering and Management, 142(8), 05016005.

Rocha, C. G. da, and Koskela, L. (2020). “Why Is Product Modularity Underdeveloped in Construction?” Proc. 28th Annual Conference of the International Group for Lean Construction (IGLC), Berkeley, California, USA, 697–708.