Structural Insulated Panels (SIP)
The Structural Insulated Panel (SIP) wall system consists of factory-made wall sections, which arrive on the building site pre-assembled and ready for installation. Although variations exist, SIPs are usually constructed from two sheets of oriented strand board (OSB) or plywood adhered to a rigid foam core of insulation. The OSB panels are typically 1/2-inch thick, while the rigid insulation board thickness typically varies from 4-8 inches, depending on the climate and performance requirements. A weather barrier is applied to the exterior before the siding is applied. Gypsum board is typically installed over the interior surface of the OSB. SIPs are capable of supporting typical loads for bearing walls, floors and roofs. They can provide both the primary structure and the envelope or they can be used with other structural systems such as post-and-beam construction to provide exterior envelope and insulation. Structural-insulated panels range in size from 4 by 8 feet to 24 by 8 feet, and are available in a variety of thickness and R-values. Typical R-value for a panel of six-inch depth is 22 compared to 19 for a typical 2x6 stud wall construction.

The advantages of this system include reduced time for assembly, improved envelope tightness, and good energy performance. SIP systems reduce energy load in two primary ways. First, the panels provide continuous insulation resulting in an envelope with few thermal bridges where heat loss occurs. Second, the panels create an envelope with fewer seams; the building shell's tightness decreases infiltration. The air leakage of a SIP-constructed home is one-third of typical new construction. These properties also increase thermal comfort of the home by eliminating cold spots and drafts. IAQ issues associated with SIP panels are minimal. Disadvantages include lack of trade familiarity with the system, higher cost compared to standard frame construction, and difficulty repairing errors in construction (such as repairs to the building envelope in the case of incorrectly located doors or fenestration openings). SIPs also have high-embodied energy from the manufacturing process. For cost and environmental implications see the Cost and Life Cycle Analyses below.

Wall System Sources
Cheple, Marilou and Pat Huelman, "Construction Technologies," House One Research Report, Minneapolis, MN: University of Minnesota, 2003.

Lstiburek, Joseph. Builder's Guide to Cold Climates, Newtown, CT: Taunton Press, 2000.

PATH Technologies, "Advanced Framing Technologies: Optimum Value Engineering (OVE)" Toolbase Services, www.pathnet.org.

Weber, William, "SIP or Stick?," Architecture Minnesota, May/June 2003