Set and Finish

Executive Summary:
Researchers investigated the two on-site phases of modular construction:
• Module set - the placement of modular home sections on a permanent foundation
• Finish - all remaining activities required to complete the home

The Set Process: Researchers observed six modular home sets. Three-person research teams spent one to three days per set and monitored and documented all set activities including start and stop times, manpower use, problems encountered and best practices. They recorded key activities by video. All six crews completed setting the modules and releasing the crane on the first day. Only one roof was completed on the set day and none of the crews completed the siding tasks on the set day.

A number of improvement opportunities were identified.

• Designs could be improved to eliminate or combine components and to eliminate potential construction interferences. This would involve combining modules, eliminating or redesigning perimeter framing around module insets, and allowing knee walls to extend when the roof is lifted. The improvements would likely reduce cycle time, site labor, enhance quality and improve energy efficiency.

• Modular manufacturing could be improved by enhancing quality and increasing content. Roof quality often slows the set process, in some cases requiring major roof rebuild. Some work could be moved back to the factory such as shingling and siding. This would add labor costs in the factory but reduce set costs on site. The question for modular manufactures is whether they can capture part of the site savings. Other activities might best be moved from the factory to the site (i.e., cleaning)

• Site logistics can be improved. There were numerous instances of cranes being repositioned and transporters being stuck on site. The crane operator should verify crane positioning and module staging before set day. Where possible, two module staging positions should be provided. A bulldozer on site to move modules would be useful.

• Fit could be improved, impacting visual appearance and energy efficiency. Factors affecting fit include: accuracy of foundations, accuracy of the set, precision of the modules, gasket placement, gasket attachment to the modules, gasket crushing, poorly fitting gable end panels and misplaced insulation. To fully seal the marriage gap between modules, both the gasket and foam needed to be used.

The Finish Process: Researchers worked with one of New England’s largest modular builders in an effort to improve their on-site modular finish process. Using findings from a kaizen rapid improvement event held in 2001, the builder has been successful in improving both the operation and the quality of their homes:

• Labor productivity improved by 59% - through a combination of improvements in the factory and better construction site supervision
• Cycle time reduced by 22% - through tighter scheduling
• Envelope tightened to 5 ACH50 – through the combined use of gaskets and foam around the marriage line

Current batch production flow.

Proposed lean single home production flow.

Although these achievements are commendable, they leave one of the greatest lean opportunities untapped – a shift from conventional, multi-home, batch scheduling toward single-home flow. As a result the construction cycle was only reduced 22% from 90 to 72 days, far from the ideal. To move closer to the lean ideal, a follow-up exercise was held with the builder, the modular manufacturer and key subcontractors. After discussing the concept of single-home flow and the tighter scheduling it requires, subs indicated a willingness to schedule each home earlier and then follow the schedule. As part of this exercise, a more definitive single-home finishing schedule was developed. The schedule showed that the cycle could be further reduced, from an average of 72 days to less than 30 days.

Technical Reports & Papers:
Mullens, M. and M. Kelley, “Lean Homebuilding Using Modular Technology,” Housing and Society, 31(1)41-54, 2004.

Mullens, M. and M. Kelley, “Lean Homebuilding Using Modular Technology,” NAHB International Builders Show: Conference Proceedings, Las Vegas, January, 2003. [download paper]

Mullens, M. “Results from Studies of the Module Set Process,” presentation given to the Quality Modular Building Task Force, Annapolis, October 2000. [download paper]

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