Structural Insulated Panels (SIPs)

Structural Insulated Panels (SIPs)


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Structural Insulated Panels (SIPs) have become a widely used alternative construction material for homes and other buildings.

While many types of Composite Panel building systems have been developed, the acronym SIPs now usually refers to panels made from a thick layer of foam (polystyrene or polyurethane) sandwiched between two layers of Oriented Strand Board (OSB), plywood or fiber-cement.

As an alternative to the foam core, SIPs are available with a core of agriculture fibers (such as wheat straw) that provides similar thermal and structural performance. The result is an engineered panel that provides structural framing, insulation, and exterior sheathing in a solid, one-piece component.

Some panel manufacturers use continuous lamination machines which automate forming and cutting according to dimensions downloaded from digital floor plans. Arriving precut to the job site, the panels can be rapidly assembled by workers without extensive training. SIPs construction allows builders to quickly construct an exterior building envelope that is strong, airtight, and energy efficient.

The basic design concept for SIPs is elegant in its simplicity, and offers several advantages for constructing walls and roofs. Bonding the foam core to the stiff outer skins creates a web-and-flange structural strength (along the same principal as an I-beam) across the length and breadth of the panel. With the capacity to handle axial, bending, racking, and shear loads, properly designed and assembled SIPs not only replace conventional framing, but will withstand high wind, and seismic forces.

Insulation capacity is another advantage of SIPs. There is general agreement that SIPs provide better overall air tightness and practical thermal performance than conventionally framed walls. Panel systems offer a dense, uniform and continuous air barrier with few thermal bridges, and no opportunity for internal convection.

Commonly, manufactured wall panels are 4 to 24 feet wide and 8 or 9 ft. high, made in standard thicknesses of 4 ½ " to 6 ½". The foam core is typically held back from the edge to allow the panel to accept 2x4 top and bottom plates. Thicknesses of up to twelve inches are available for roof panels where greater R-value is needed. The core material of thicker panels usually corresponds to standard lumber dimensions, so that board stock may be used for splines and plates. Panel lengths can vary to accommodate higher ceilings or roof spans up to 24 ft.

Many manufacturers maintain a standard panel width of 4 ft. for ease of transportation and handling, but wider panels are sometimes designed to accommodate door and window openings. Alternatively, rough openings for doors may be created by placing header sections between full-length wall panels. Window opening can be made in a similar fashion with the addition of a base panel. Dimensional lumber usually frames out rough openings. For wider openings, headers with greater load bearing capacity may be needed. Insulated Headers using sandwiched foam have been specially designed to work in conjunction with SIPs.

Some manufacturers now offer special variations in SIPs products, such as a high-end panel made with an injected polyurethane core, and vertical joint connectors featuring eccentric cam locks that draw the panels tightly together and assure proper alignment. Manufacturers can also produce curved walls or other customized architectural features.

Benefits/Costs
Several benefits have made SIPs a viable and popular alternative to conventional construction methods. The ease and speed of assembly makes it possible for houses to be placed under roof within days rather than weeks. While basic carpentry skills are required, assemblers need not have the skill levels of conventional framing crews, which can further reduce costs to builders. SIPs structures are highly resistant to wind damage, and suitable for areas with stringent windshear or seismic codes. The thermal performance of SIPs may significantly reduce costs for heating and air conditioning, one of the major expenses of home ownership.

Use of SIPs panels can help conserve scarce timber resources, since they provide good structural performance using significantly less dimensional lumber. The lumber used for manufacturing OSB comes from fast growing trees that can be planted and harvested in just a few years.

Reduced energy use from the efficiency of SIPs insulation also translates to the conservation of resources, and manufacturers state that the foam products used for the core materials are environmentally benign.

Costs can be significantly higher for customized layouts. The installation of electrical wiring and plumbing lines may require special tools and techniques. Because SIPs panel structures are more airtight, special attention should be paid to mechanical ventilation design to avoid potential backdrafts. Extra care should also be taken to see that gas appliances are properly vented.

Source: NAHB Research