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Structural insulated panels (or structural insulating panels), SIPs, are a composite building material. They consist of a sandwich of two layers of structural board with an insulating layer of foam in between. The board is usually Oriented Strand Board (OSB) and the foam either polystyrene foam or polyurethane foam.

SIPs allow the application of an internal and external structural skin and thermal insulation to a building in one stage, offering efficiency benefits. They are commonly used in conjunction with modern timber framed buildings.

History

Although foam-core panels gained attention in the 1970s, the idea of using stress skinned panels for construction began in the 1930s. Research and testing of the technology was done primarily by Forest Products Laboratory (FPL) in Madison, Wisconsin as part of U.S. Forest Service's attempts to conserve forest resources. In 1937, a small stressed-skin house was constructed and garnered enough attention to bring in First Lady Eleanor Roosevelt to dedicate the house. In a testament to the durability of such panel structures, it has endured the severe Wisconsin climate and is currently being used by University of Wisconsin as a day care center. With the success of the stress skinned panels, it was suggested stronger skins could take all of the structural load and eliminate the frame altogether.

Thus in 1947, structural insulated panel development began with corrugated paperboard cores were tested with various skin materials of plywood, tempered hardboard and treated paperboard. The building was deconstructed in 1978 and most of the panels retained their original strength with the exception of paperboard which is unsuited to outdoor exposure. Panels consisting of polystyrene core and paper overlaid with plywood skins were used in a building in 1967 and the panels have performed well to the present day.

Then in the early 1980s "Hoot" Haddock, a former construction manager for the Alaska pipeline, began research on a cement skinned panel system called ThermaSAVE to withstand the harsh Alaskan climate.

Materials

SIPS are most commonly made of OSB panels sandwiched around a foam core made of either expanded polystyrene(EPS) or rigid polyurethane foam, but other materials are used. Some SIPS will use fiber-cement or plywood for the panels and agricultural fiber, such as wheat straw, can be used for the core.

Fiber-cement faced SIPS have several benefits that can outweigh the higher cost compared to an OSB faced panel. They last longer and require less maintenance, will not rot, burn, or corrode, typically does not require drywall, are vermin resistant and do not support black mold growth.

In areas where termites are a concern, termiticide can be included in the foam during manufacture.

The foam used, although slow to ignite, once lit emits a dark smoke that contains toxic gases, and as such gypsum board is required to provide a fire barrier. EPS does not off gas and is dimensionally stable, as well as its manufacture does not produce any o-zone harming chemicals.

Benefits and drawbacks

The use of SIPS brings many benefits and some drawbacks when compared to a conventional stick framed building. A well built home using SIPS will have a tighter building envelope and the walls will have a higher insulative value, which leads to fewer drafts and a decrease in operating costs for maintaining a comfortable interior environment for the occupants. Also, due to the standardized and all-in-one nature of SIPS construction time can be reduced over building a stick frame home as well as requiring fewer trades for system integration. The panels can be used as floor, wall, and roof, with the use of the panels as floors being of particular benefit when used above an uninsulated space below.

An OSB skinned system outperforms conventional stick framed construction structurally and maintain the versatility of the stick framed house when incorporating custom designs. Also, since SIPS work as framing, insulation, and exterior sheathing, and can come precut from the factory for the specific job, the exterior building envelope can be built quite quickly.

Dimensions and characteristics

Dimensionally SIPS tend to come in sizes from 4 feet to 24 feet in width. Much of the time manufacturers produce the 4 feet sections to ease in transportation and handling but the use of the longest panel possible will create the most efficient SIPS building. At between three and four pounds per square foot, longer panels can become difficult to work with out the use of a crane to position them, and this is a consideration that must be taken into account due to cost and site limitations. Also of note is that when needed for special circumstances longer spans can often be requested, such as for a long roof span. Typical height for panels is eight or nine feet. Wall panels tend to come in thicknesses between 4.5 and 6.5 inches, but can be made up to a foot thick for roofs.

EPS is the most common of the foams used and has an R value between 3.6 to 3.8 per inch. Which would give the 3.5 inches of foam in a 4.5 inch thick panel an R value of 12.6. This at face value appears to be comparable to an R-13 batt of fiberglass, but due to the fact that in a standard stick frame house there is significantly more wall containing low R value wood that acts as a cold bridge, the thermal performance of the R-12.6 SIPS wall will be considerably better.

See also

• ThermaSAVE

External links

• Structural Insulated Panel Association – Industry association for manufacturers of SIPs
• PATH Tech Inventory: Structural Insulated Panels
• PATH Tech Inventory: Fiber-cement Faced Structural Insulated Panels

• Building engineering
• Construction
• Composite materials