A structural insulated panel (SIP) is a panel of thick, rigid, foam insulation sandwiched between two structural skins of plywood boards. SIPs can be used for walls, floors, and roofs in both residential and commercial buildings. The SIP panel looks like a rectangular sandwich, with the two layers on the outside and the filling in between (see image below).
This structural sandwich is typically made with an inner core of expanded polystyrene (EPS) insulation between two structural skins of oriented strand board (OSB), which is made up of small scraps of wood glued together into a panel. The OSB uses less wood than standard plywood, and the EPS is inflated without ozone-depleting chemicals, making this a greener product than the typical wall of wood framing and plywood.
SIPs are available in a variety of alternative insulation cores and skin materials. They are manufactured under strict factory-controlled conditions. Because they’re premade, the panels arrive at the construction site strong, precisely cut, and very dimensionally stable. That means they won’t shrink or warp from water or temperature the way that traditional wood does.
The sandwich of a SIP is equivalent to the wood framing, sheathing, and wall insulation of a traditional home, all in one simple panel. Because each panel is a preformed structural wall, the finished building is much stronger than a traditional wood-frame house and can be put together much faster. Building with SIPs can speed up your construction time, reduce waste, and decrease the amount of labor.
The History of Structural Insulated Panels
The first foam-core panels appeared in the 1930s, when they were called “stressed skin panels.” They were the product of research by the U.S. Forest Service. The panels were created to reduce the use of wood resources. First Lady Eleanor Roosevelt dedicated a small stressed-skin house in 1937, bringing attention to this new technology.
Although standardized SIPs have been around since the 1950s, they didn’t catch on in the construction industry until the 1980s. Production and tract-home builders have recently fallen in love with the technology, and the use of SIPs has grown steadily.
Early SIPs were made up of plywood skins glued to both sides of Styrofoam insulation. Today’s SIPs are made with either 7/16-inch or 5/8-inch oriented strand board (OSB) skins factory glued to expanded polystyrene (EPS) insulation cores.
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