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How Structural Insulated Panels Work

Making the Magic Happen: Inside a Structural Insulated Panel
Architectural blueprints can be digitally created to provide instructions for manufacturers to cut prefab SIPs.
Architectural blueprints can be digitally created to provide instructions for manufacturers to cut prefab SIPs.
Vasko Miokovic/iStockphoto

­Ready to crack a panel open and see what makes it tick? The core of an SIP panel is usually created out of foam (sort of like the creamy goodness inside an Oreo cookie) and is most frequently made of expanded polystyrene (EPS) foam board [source: U.S. Department of Energy]. Other common materials are polyurethane and polyisocyanurate, which tend to be mo­re expensive but offer greater insulation, provide a better moisture barrier and are more resistant to fire. The core can alternatively be comprised of other elements like compressed straw, which is more environmentally friendly and renewable but also heavier and less insulating.

If you've stopped to consider a home's electrical system, you might be scratching your head right about now. If the walls are solid panels, are the wires strung up around the house like Christmas lights? Not quite. During manufacturing, narrow channels typically known as chases or wirechases are either formed directly into the foam or tunneled out later. Wires can be strung through these conduits and along other inlaid niches.

As we read on the last page, oriented strand board made from fast-growing trees is commonly used as a structural skin, although plywood, fiberglass and cementboard are among the other options. Something else to note: During construction, siding and roofing aren't the only components that'll be flushing out the look of your SIPs. Gypsum board and other fire-rated materials are usually applied on the inside to help slow a blaze in the event of a house fire.

In the production process, the two sections of sheathing and the foam core are sandwiched together and cut to the proper size specifications. These can be standard dimensions or kits customized for a particular job. Manufacturers might cut window and door openings, or leave that to the construction crew. The panels are sometimes labeled for easy assembly -- sort of a paint-by-number setup -- and then they're ready to be shipped to the site.

Although there are industry standards, SIPs are highly customizable in shape, density, size, thickness and appearance. They can be used for residential homes as well as light commercial buildings. On the next page, we'll find out how SIP projects are assembled and some of the advantages they offer.