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-Madison 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 dismantled 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 can be used. Some SIPs use fiber-cement or plywood for the panels, and agricultural fiber, such as wheat straw, 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 do 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 offgas, is dimensionally stable, and its manufacture produces no ozone-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.
The EPS insulation is a closed cell insulation as compared to fibreglass insulation which is an open cell insulation. Both insulations R-values are tested in a laboratory under steady state conditions where there is no air infiltration. When a SIP is installed as a wall, foundation, floor or roof system, the EPS is installed in a steady state environment, where as fiberglass insulations are installed in a non-steady state environment because these wall, foundation, floor and roof systems have to be vented to remove moisture. Many research studies show that the R-values of fibreglass insulation decrease as the temperature differential of indoor and outdoor temperatures increase resulting in higher energy costs to the homeowner. (TAKEN FROM WIKEPEDIA)
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