Structural Insulated Panels

Avalon Building Systems, Inc. was the designer and builder of the very first "modular SIPS" home in the United States. This "hybrid" home was built in Douglas, MA in 2008. R40 polyurethane core structural insulated panels were used that were produced by The Murus Company, Inc. of Mansfield, PA and the modular home was manufactured by Penn Lyon Homes, Inc. of Selinsgrove, PA. The home was built to easily exceed "Energy Star Standards" and was also certified to be built to meet LEEDS platinum standards for new residential construction. LEED is an internationally recognized certification system that measures how well a building performs across all the metrics that matter most: energy savings, water efficiency, CO2 emissions reduction, improved indoor air quality, and stewardship of resources and sensitivity to their impacts. LEED certification is based on a point system in which a building can obtain a Certified, Silver, Gold or Platinum level certification.

Structural Insulated Panels

Structural Insulated Panels (SIPs) are prefabricated insulated structural elements for use in building walls, ceilings, floors, and roofs. They provide superior and uniform insulation compared to more traditional construction methods (stud or "stick frame"), offering energy savings of 12%–14%. When installed properly, SIPs also provide a more airtight dwelling, which makes a house more comfortable and quieter.

SIPs not only have high R-values but also high strength-to-weight ratios. An SIP typically consists of 4- to 8-inch thick foam board insulation sandwiched between two oriented strand boards (OSB) or other structural facing materials. Manufacturers usually can customize the exterior and interior sheathing materials according to customer requirements. The facing is glued to the foam core. The panel is then either pressed or placed in a vacuum to bond the sheathing and core together.

SIPs can be produced in various sizes or dimensions. Some manufacturers can make panels as large as 96×288 inches, which require a crane to erect.

The quality of SIP manufacturing is very important to ensure a long life and performance. The panels must be glued, pressed, and cured properly to ensure that they don't delaminate. The panels also must have smooth surfaces and edges to prevent gaps from occurring when they're connected at the job site. Before purchasing SIPs, ask manufacturers about their quality control and testing procedures. Read and compare warranties carefully.

Types of SIPs

The most common types of SIPs use insulation made from expanded polystyrene or polyisocyanurate, a polyurethane derivative. You can also find SIPs with a compressed, insulating straw core.

Some manufacturers are examining ways of using cementitious and rigid fibrous insulating materials.

Expanded Polystyrene Insulated Panels

The majority of SIPs are manufactured with expanded polystyrene (EPS) foam board or beadboard insulation. This type of SIP has a nominal R-value of about 4 per inch (2.5 cm) to 5 per inch of thickness.

They are available in almost any size; however, common wall panels are 48×96 inches and weigh 110 pounds (50 kilograms [kg]).

Polyisocyanurate and Polyurethane Insulated Panels

Some manufacturers choose to use polyisocyanurate or polyurethane as the insulating material. Foam board or liquid foam can be used to manufacture an SIP. Liquid foam can be injected between two wood skins under considerable pressure. When hardened, the foam produces a strong bond between the foam and the skins.

Polyurethane and polyisocyanurate SIPs have a nominal R-value of around R-6 to R-7 per inch (2.5 cm) of thickness. Liquid foams contain a blowing agent, some of which escapes over time, reducing the initial R-value of the SIP from about R-9 to R-7.

Wall panels made of polyisocyanurate or polyurethane are typically 3.5 (89 mm) thick. Ceiling panels are up to 7.5 inches (190 mm) thick. These panels, although more expensive, are more fire and water vapor-diffusion resistant than EPS. They also insulate 30%–40% better per given thickness.

Compressed Straw Core Insulated Panels

Straw SIPs are more environmentally friendly than the other types because they're made from renewable, recycled waste agricultural straw. However, straw SIPs offer less insulation per inch of thickness, and they are considerably heavier.

SIP Installation

SIPs are made in a factory and shipped to job sites or to manufacturing facilities. Builders or manufacturers then connect them together to construct a house. The speed of construction when using SIPs is much faster than other types of residential construction, especially if the builder is familiar with them. Shells can be erected quickly, saving labor time and money, without compromising quality. These savings can help compensate for the fact that SIPs usually cost more than other construction systems, but through the "modular" manufacturing process many efficiencies are recognized and the cost premium is greatly minimized with a relatively quick payback period.

Many SIP manufacturers also offer "panelized housing kits." The builder needs only to assemble the pre-cut pieces. Additional openings for doors and windows can be cut with standard tools at the construction site.

When installed according to manufacturers' recommendations, SIPs meet all building codes and pass the American Society for Testing and Materials (ASTM) standards of safety. In buildings constructed of SIPs, fire investigators have found that the panels held up well. For example, in one case where the structure exceeded 1,000°F (538°C) in the ceiling areas and 200°F (93°C) near the floors, most wall panels and much of the ceiling remained intact. An examination of the wall panels revealed that the foam core had neither melted nor delaminated from the skins. In similar cases, a lack of oxygen seemingly caused the fire to extinguish itself. The air supply in a structural insulated panel home can be quickly consumed in a fire.