SIP  - Structural insulated panels

SIPs consist of a sandwich of two layers of structural board with an insulating layer of foam in between. The board is usually Oriented Strand Board (OSB) and the foam either polystyrene foam or polyurethane foam.

SIPs allow the application of an internal and external structural skin and thermal insulation to a building in one stage, offering efficiency benefits. They are commonly used in conjunction with modern timber framed buildings

SIPs are most commonly made of OSB panels sandwiched around a foam core made of either expanded polystyrene (EPS) or rigid polyurethane foam, but other materials can be used. Some SIPs use fiber-cement or plywood for the panels, and agricultural fiber, such as wheat straw, for the core.

Fiber-cement faced SIPs have several benefits that can outweigh the higher cost compared to an OSB-faced panel. They last longer and require less maintenance, will not rot, burn, or corrode, typically do not require drywall, are vermin-resistant and do not support black mold growth.

In areas where termites are a concern, termiticide can be included in the foam during manufacture.

The foam used, although slow to ignite, once lit emits a dark smoke that contains toxic gases, and as such gypsum board is required to provide a fire barrier. EPS does not offgas, is dimensionally stable, and its manufacture produces no ozone-harming chemicals.

The use of SIPs brings many benefits and some drawbacks when compared to a conventional stick framed building. A well built home using SIPs will have a tighter building envelope and the walls will have a higher insulative value, which leads to fewer drafts and a decrease in operating costs for maintaining a comfortable interior environment for the occupants. Also, due to the standardized and all-in-one nature of SIPs construction time can be reduced over building a stick frame home as well as requiring fewer trades for system integration. The panels can be used as floor, wall, and roof, with the use of the panels as floors being of particular benefit when used above an uninsulated space below.

An OSB skinned system outperforms conventional stick framed construction structurally and maintain the versatility of the stick framed house when incorporating custom designs. Also, since SIPs work as framing, insulation, and exterior sheathing, and can come precut from the factory for the specific job, the exterior building envelope can be built quite quickly.

The EPS insulation is a closed cell insulation as compared to fibreglass insulation which is an open cell insulation. Both insulations R-values are tested in a laboratory under steady state conditions where there is no air infiltration. When a SIP is installed as a wall, foundation, floor or roof system, the EPS is installed in a steady state environment, where as fiberglass insulations are installed in a non-steady state environment because these wall, foundation, floor and roof systems have to be vented to remove moisture. Many research studies show that the R-values of fibreglass insulation decrease as the temperature differential of indoor and outdoor temperatures increase resulting in higher energy costs to the homeowner.

Dimensionally SIPS tend to come in sizes from 4 feet to 24 feet in width. Much of the time manufacturers produce the 4 feet sections to ease in transportation and handling but the use of the longest panel possible will create the most efficient SIPS building. At between three and four pounds per square foot, longer panels can become difficult to work with without the use of a crane to position them, and this is a consideration that must be taken into account due to cost and site limitations. Also of note is that when needed for special circumstances longer spans can often be requested, such as for a long roof span. Typical height for panels is eight or nine feet. Wall panels tend to come in thicknesses between 4.5 and 6.5 inches, but can be made up to a foot thick for roofs.

EPS is the most common of the foams used and has an R value between 3.6 to 3.8 per inch, which would give the 3.5 inches of foam in a 4.5 inch thick panel an R value of 12.6. This at face value appears to be comparable to an R-13 batt of fiberglass, but due to the fact that in a standard stick frame house there is significantly more wall containing low R value wood that acts as a cold bridge, the thermal performance of the R-12.6 SIPS wall will be considerably better