Benchmarking SIPs for Habitat for Humanity
Executive Summary:
The objective of this study was to compare the construction processes of two homebuilding systems, structural insulated panels (SIPs) and conventional 2x4 stick-built. SIPs are made with insulative foam sandwiched between oriented strandboard (OSB). Energy studies have demonstrated that SIPs can produce more airtight and energy efficient homes. SIP suppliers also promise significant construction advantages, however, little scientific data is available to substantiate claims. The study focuses on the construction of two similar single-family homes, one SIP and one stick-built, built by Habitat for Humanity during Fall 1997. The study documents two key measures of construction performance, cycle time and labor man-hours. The study addresses only those activities on the construction site and focuses on the framing process (rather than finishing), since the primary impact of the building system occurs during framing.The SIP home, built in Sedro-Woolley, Washington, was a 1,293 square-foot, four-bedroom home. The floor, walls and roof were constructed using SIPs. Panels were delivered to the construction site with many factory value-added features including pre-cut panels (length, width, gables, windows/doors openings), pre-framed window/door openings, and pre-installed splines in the wall panels. The 2x4 stick-built home, built outside Plains, Georgia, was a 1,064 square-foot, four-bedroom home. While the majority of the home was stick built on site, some sub-assemblies, including roof trusses and window frames, were completed in the Habitat “factory” in Americus. Floor framing was not required due to slab-on-grade construction.
After being normalized by the square footage in each home (to account for design differences), the data indicate that the SIP home saved 65% of the site labor when compared to the stick-built home. Cycle time savings are of similar magnitude. Volunteers were interviewed after framing the SIP house to gauge their perception of SIP construction. The results suggest that both construction professionals and other volunteers believed that SIPs reduced construction effort significantly, averaging about one-half the effort of conventional stick-built construction.
Technical Reports & Papers:
Mullens, M. and M. Arif, Final Report: Results of a Construction Process Analysis of Structural Insulated Panels versus Stick-Building, Report to U.S. DOE, Department of Industrial Engineering and Management Systems, University of Central Florida, Orlando, FL, December 1998. [download this report]Mullens, M. and M. Arif, “Structural Insulated Panels: Impact on the Residential Construction Process”, The Journal of Construction Engineering and Management, 132(7) 786-794, July 2006.
