Structural Insulated Panels

Where insulated concrete form construction creates a concrete wall surrounded by insulating foam, structural insulated panels (SIPs) sandwich a layer of polystyrene or polyurethane foam between two layers of structural board. The board is usually oriented strand board (an engineered wood product like plywood), but can also be plywood, sheet metal, drywall, finished lumber or cement board. Whatever the outer covering, the result is a rigid, load-bearing, well-insulated building module that can be trucked to a jobsite on a flatbed trailer like an oversized mattress. SIPs combine the structure framing, insulation, vapor and air barrier and sheathing into one unit than can be used for roofs, walls or floors.

Section of structural insulated panels

The foam core and exterior facings are typically glued together, precut in a factory and delivered to the site ready for assembly. Units come in standard thicknesses ranging from 4 inches to 6 inches, in lengths from 4 feet to up to 28 feet, and can be up to 9 feet tall. Some manufacturers also make custom sizes, although these cost more.

Some companies will custom cut and create SIPs for your project from your plans, delivering a ready-to-assemble project that can even have electrical boxes and conduit preinstalled. Windows and doors can be prebuilt into the panels at the factory or cut at the jobsite.

Panels at the construction site are glued together with slender plywood-like splines, and two-by lumber is used as a top and bottom plate. No studs are used in the walls - the panels themselves provide the building's structural support. As a result, the panels greatly reduce the amount of lumber needed to build a house. In addition, construction is faster and less labor intensive. Usually there is less construction waste using the panels, which are created in a factory under carefully controlled, exacting conditions. Unlike studs, SIPs don't warp over time, making for straight, even, well-insulated walls.

Installing structural insulated panels

A SIP roof automatically creates an unvented, conditioned attic, which can be used for living space or HVAC equipment. Factyory-made foam sandwich panels.

SIPs share the same structural properties as an I-beam or I-column. The rigid insulation core of the SIP acts as a web, while the outer sheathing operates as the flanges.

SIPS provide a strong building system, one that stands up well to storms. When glued and fastened together, the panels form a shell of virtually solid insulation, without the breaks and voids caused by building with studs. Since these breaks are normally where energy leaks occur, homes build this way are extremely energy efficient and quiet. The continuous wood surface on both sides of the wall makes for a sound nailing base for every type of exterior and interior finish.

There are a number of companies that manufacture SIPs. The Structural Insulated Panel Association lists companies and provides more information.