In the last article we discussed the different (most-common) types of sheathing for SIPs, but just as there are different sheathings there are also different foam cores. In this article we’ll look at the three main cores there are in the structural insulated panel industry: polyurethane, expanded polystyrene (EPS), and extruded polystyrene (XPS).

Polyurethane: With 6 to 6.8, this foam core has the highest R-value per inch of the three I’ve mentioned. Another advantage is its high melting point; in a fire, it would be the last thing standing. However, polyurethane foam is expensive at nearly 40 cents per square inch of panel, Also, the hot wire burners that are used for on-site adjustments can’t be used because of the melting point.

Expanded Polystyrene (EPS):EPS is the most common type of foam core for SIPs. It is cheap, widely available, and most installers are acquainted with it. However, like many readily available things, there are trade-offs. It has the lowest R-value and melting point.

Extruded Polystyrene (XPS): XPS is a nice in-between when compared to the above two foams. It has a high R-value (5 per inch of panel) while still having a rather low melting point so on-site tweaks can still be made. Something this good has to have a bad point though, and this is no exception: XPS is expensive and hard to find.

Source.

Let’s take a closer look at some of the various aspects of structural insulated panels. The materials that SIPs are made of make a difference in several ways. In the last article, I mentioned that SIPs could be made of OSB, metal, cement-board, and fiber-glass.

OSB: Oriented Strand Board is made from sustainable fast-growing trees, and is the most common type of sheathing material for SIPs.

Metal: Stainless steel and G90 galvanized are the most common metal sheathing used for SIPs. Long-term it’s probably best to go with stainless. (Source)

Cement-board: Typically made of cellulose, reinforced, cement boards, the fire-resistance eliminates the need for gypsum drywall. These are so strong that headers above the windows and doors are unnecessary. They are generally as efficient as OSB panels. Cement-board SIPs typically last longer and require less maintenance than other types of SIPs. They also have good resistance to moisture absorption. This type of sheathing is slightly more expensive than OSB SIPs. (Source)

Fiber-glass: Fiber-glass sheaths are bonded to PVC or studs for support, and consist of polymer-based resins blended into a reinforcing frame of structural glass fibers. The sheaths are thin, but quite strong. (Source) (This one is not nearly as common as the previous sheathing materials mentioned.)

What are SIPs? SIPs, or structural insulated panels, are composed of a thick, rigid-foam core sandwiched between two sheets of OSB (Oriented Strand Board), metal, cementboard, or fiberglass. Created to be a high-performance, energy-saving building material, SIPs can be custom designed for each home.

Cost of SIPs? SIPs construction costs about the same as traditional construction when you figure in the labor savings for a shorter construction time. SIPs allow the HVAC to be smaller, which would also bring savings during the construction period. However, the greatest savings will be through the years with reduced energy bills (even up to 50%! source)

The History of SIPs: SIPs aren’t new. In fact, Frank Lloyd Wright used them in some of his Usonian houses in the 1930s and ’40s. When one of his students, Alden B. Dow, the son of the founder of Dow Chemical Company, created the first foam core SIP in 1952, SIPs jumped into the technological world. In the ’60s, SIPs became readily available, resulting in the building material we know today. (Source)

Wiring SIPs: As could be expected, wiring is different with SIPs. The manufacturer cuts chases, or channels, according to the house design during the manufacturing process, through which the wire is pulled.