Mass Customization Using Modular Homebuilding

Executive Summary:
This research conceptualizes and assesses the viability of a new approach for the mass customization of housing. The approach seeks to enhance pre-fabricated modular building systems by incorporating the open building concepts of shell/infill layering and disentangling. Concepts are explored in the context of a mid-rise, multi-family urban housing project, the housing type expected to become dominant in the U.S. as baby boomers retire. The research includes the schematic design of the larger system, the identification/design of selected components, and the assessment of needed changes to existing processes including factory manufacturing, on-site construction and ongoing remodeling.

Research results suggest the new methodology is an efficient homebuilding approach that better meets the challenges and opportunities of the future by providing tailored living environments that can more gracefully accommodate changing activities, needs, and technologies. More specifically, results indicate that the approach is feasible, although changes in materials and construction processes are necessary. Innovative materials and components provide the structure necessary to apply open building concepts. Primary building components recommended include open-web ceiling joists and factory-built integrated interior infill (I3) components used to construct interior walls. The I3 components include movable framed interior walls, commercial open-office walls and cabinet walls. The latter two elements are part of highly engineered, vendor-supplied wall systems. Innovative utility solutions complement the new building components, disentangling utilities from structural systems and other utilities. Utility solutions include a high velocity forced air distribution system that uses 4” mini-ducts, centralized wiring runs in the ceiling of each module, a surface-mounted baseboard wiring system, wireless controls for ceiling fixtures, flexible PEX freshwater plumbing lines, and wireless communications (telephone/cable/data).

Although these innovative components cost more than their conventional counterparts, they are likely to reduce factory manufacturing and on-site construction effort. The primary reason for incorporating open building concepts in modular homebuilding is to simplify remodeling. Remodeling efforts will be greatly simplified with the new system:

• The continuous finished floor permits walls to be relocated without affecting flooring.
• The I3 wall design coupled with disentangled utility strategies (e.g., surface-mounted baseboard wiring system for wall outlets and wireless communications)  permit walls to be easily added, removed, or relocated. Only minor repairs for the floor, ceiling, and wall interfaces may be required.
• The combination of open-web ceiling joists and the miniducts used by the high velocity HVAC system effectively eliminate soffits in the unit.
• The combination of open-web ceiling joists, wireless ceiling fixture controls, centralized wiring paths, and spare circuits greatly reduce the effort and minimize damage when adding or relocating ceiling fixtures.

This research has several limitations. First, it focuses on specialized modular homebuilding technologies that are suitable for mid-rise applications - steel framing and concrete floor decks. This technology is not used in mainstream modular homebuilding in the U.S. A second shortcoming is the lack of quantitative data that allows costs to be better understood when considering design alternatives and tradeoffs. A final shortcoming is the focus on existing components that can address open building needs. Future research should address these shortcomings. The same open building concepts and design solutions should be explored to assess how they can apply to more conventional wood frame modular homebuilding technologies used for single family and low-rise multi-family applications. Costs should be more thoroughly examined and estimated, permitting tradeoffs between first cost and remodeling flexibility. Finally, new and more innovative designs should be considered for all components that can facilitate the integration of open building concepts into modular homebuilding. Prime examples include I3 wall, surface-mounted wiring, HVAC, and structural components.

This research yielded several additional products. An important element of this study was an analysis of the current modular production process to assess its efficiency and identify opportunities for introducing lean production concepts into the operation. Recommendations were presented to factory management and a follow-up kaizen rapid improvement event was organized and executed

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Technical Reports and Papers:
 Mullens, M. “An Industrialized Solution for U.S. Urban Housing,” Proceedings of the U.S – India Symposium on Urban Housing and Supporting Infrastructure, National Science Foundation, U.S.A and Ministry of Science and Technology, India, Oct. 20-22, 2005, New Delhi, Construction Management Program, Michigan State University, MI. [download paper ]

Mullens, M., Hoekstra, R., and Nahmens, I. An Integrated Interior Infill System for Mass Customized Housing, Report to the National Science Foundation, Washington, D.C., September, 2005. [download paper]

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