Perspectives
In contrast to DESIGNhabitat 2, 100% of the conditioned area in the DESIGNhabitat 2.1 house was constructed in the factory; although some interior finishing was required achieve the vaulted ceiling in the main living area. The site-constructed elements included the front porch, and the section of roof required to join the two modules at the attic level. Other differences in the two designs included an additional bath in the 2.1 house, factory-installed cabinets (they were student-built in the 2.0 house), and a more complex module setting procedure for the DESIGNhabitat 2.1 house (in the 2.1 design, the crane was required to lift the hinged roofs).
As expected, the DESIGNhabitat 2.1 house cost more than DESIGNhabitat 2.0 ($75 / SF vs. $68 SF) primarily because the second house relies on a “for profit” production process to build more of the home. In order to more closely understand how the differences in the “blend” on modular and site-built elements impacted the project cost, we can isolate the elements of the cost history for each home that were not influenced by the choice of approach (such as site work, foundations, electrical, plumbing, HVAC, etc.).
In this analysis, the combination of the modular component costs and the cost of site-constructed elements for the DESIGNhabitat 2.0 amount to approximately $48/SF. The same combination of elements on the DESIGNhabitat 2.1 house cost $58/SF. This helps frame the “premium” associated with increasing the area of factory-built SF from 65% to 100% at $10/SF. From another angle, we increased the factory-produced area by 35%, at an increase in cost of about 21%. While this analysis does not account for all the differences between the two designs (such as the extra bath, kitchen elements, complexity of site-built elements, etc.), it does give some perspective on the cost consequence of shifting from a blend of factory and site-built elements to an emphasis on maximizing the factory-produced area.
The other element of the “hypothesis” of DESIGNhabitat 2.1 was that the shift to more factory-produced area would be off-set by a reduction in the on-site volunteer hours required to complete the house. Unfortunately, the delay in delivery of the modules threw the on-site construction phase outside of the planned window, and the team lost the ability to structure the volunteer work effort in a manner comparable to the approach utilized on the DESIGNhabitat 2.0 house.
