The Home Building Industry's Technical Information Resource

Back to Standard View
Search TechnologiesAbout Technology Inventory
Browse by Building System

Symbol Legend
Adobe Acrobat Reader required for PDF documents

PDF documents require the free Adobe Reader.

All PDF documents open in a new browser window. Close the browser window to return to the site.

Structural Insulated Panels (SIPs)

Panels made from a thick layer of foam (polystyrene or polyurethane) sandwiched between two layers of Oriented Strand Board (OSB), plywood or fiber-cement.

View the ToolBase TechSpecs- Structural Insulated Panels PDF file for an overview of this technology.

Structural insulated panel

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 (see separate PATH Technology Inventory article), 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 floorplans. Arriving precut to the jobsite, 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 (separate PATH Technology Inventory article) 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.

Energy Efficiency

SIPs genarally contain higher R values than a similarly sized wall, improving thermal performance. By being very airtight, they also allow little infiltration, adding to the thermal performance.

Kind of difficult

There are several dozen manufacturers, shipping SIP products throughout the United States.

As previously mentioned, 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.

When SIPs panels are used for roof construction, standard roof sheathing ventilation practices cannot be used. Some shingle manufacturers will not warrant products placed on sheathing without air circulation beneath. To address this concern, some roof panels have been constructed with channels in the core material, running underneath the upper sheathing layer. There has been at least one report of SIP roof panel failure due to moisture deterioration in the extremely damp and rainy climate of Juneau, Alaska. However, the Structural Insulated Panel Association (SIPA) asserts that standard SIPs panels will not deteriorate if properly installed.

Some manufacturers offer prefabricated SIPs home packages at costs approaching those for conventionally framed structures. However, the cost of producing and engineering panel layouts may drive up costs for custom designs. While some panel modifications onsite are possible, they are usually more difficult and costly than for conventional framing.

Not Applicable

Currently there is no specific prescriptive language in building codes addressing SIPS. However, prescriptive guidelines and code provisions are being developed by SIPA. The majority of manufacturers provide technical design and support services to ensure code acceptance. An ICC-ES report on the panel should be obtained and furnished at plan review. Information on ICC-ES reports can be obtained through the links below.

Carl Franklin Homes: The Vista at Kensington Park, Dallas, Texas

SIPs construction relies on careful planning and design prior to delivery and site assembly. Several companies offer pre-designed house packages with wall and roof panels of standardized dimensions to help control costs. For custom designs, a completely customized panel layout must be produced. Some panel manufacturers uses computer controlled equipment that transfers panel cutting instructions directly from digital CAD (computer aided design) drawings.

Panels are shipped to the jobsite for assembly when the foundation and deck are in place. Ideally, panels are offloaded and stacked in the exact reverse order needed, so that no sorting or shuffling is required. After the bottom plate is attached to the perimeter, placement of the wall panels begins. Panels weigh approximately three pounds per square foot, so 4’ panels are light enough to be carried and set by hand. Exterior walls for most houses can be erected in less than a day. Nails and adhesive foam are used to fasten the panels to top and bottom plates, and to make vertical connections. Gutter spikes or long screws are often used for SIP corner connections. Walls must be properly braced and plumbed, and interior walls are typically constructed with conventional framing. Beams that carry roof loads may require stud supports incorporated into wall panels, to carry point loads downward. Heavier roof panels are usually set in place with a crane.

To take full advantage of SIPs insulating capacity, care must be taken to seal all joints properly, but the relatively small number of connections makes this easier to accomplish. Spray polyurethane foam is often used to fill any voids or gaps, but some manufacturers specify gaskets or other caulking materials. SIPA, the Structural Insulated Panel Association, provides "best practice" connection diagrams for typical joints and details.

Some trades may find their work made simpler by SIPs construction. For instance, drywall and siding installers need not worry about locating studs. Others, such as electricians, may need to make special accommodations. Most panels include a formed chase in the core for electric wiring, but insets for boxes and additional channels must be mechanically routed, then resealed with aerosol foam. Generally, best practices for plumbing design route pipes through interior walls, but if placement of pipes in near exterior walls is necessary, significant routing and foaming may be required.

Not Applicable

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.

Disclaimer: The information on the system, product or material presented herein is provided for informational purposes only. The technical descriptions, details, requirements, and limitations expressed do not constitute an endorsement, approval, or acceptance of the subject matter by the NAHB Research Center. There are no warranties, either expressed or implied, regarding the accuracy or completeness of this information. Full reproduction, without modification, is permissible.