Environmental Impact, Structural Insulated Panels

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Getting More from Less

With so many people concerned about deforestation, you might not expect wood products to be the first things mentioned in this book. But some engineered wood products like these are made more efficiently. The result is high-quality new construction and remodeling with reduced overall consumption of natural resources.

According to APA, an industry group, wood products make up nearly half of the industrial raw materials manufactured in the United States, but consume only four percent of the energy needed to manufacture those materials. The forest products industry recognizes
the importance of trees—not just after they are harvested, but while they are growing. For every ton of wood grown, a young forest produces 1.07 tons of oxygen and absorbs 1.47 tons of carbon dioxide. Recent figures show that, for every 100 trees harvested, 125 are
planted.

Making a Sandwich

Structural insulated panels (SIPs) are ready-made sections for use in walls, roofs, or even floors. They are also known as foam core panels or sandwich panels. Several varieties are available, with slight differences in materials and applications. All SIPs feature a layer of foam insulation sandwiched between and bonded to two sheets of wood, usually oriented strand board or plywood.

 

The foam insulation offers an effective barrier against heat, cold, and sound; the wood sheets provide strength and stability. The panels deliver high insulating and structural performance with light weight. These versatile panels can be used in place of traditional wall framing, roof decking, and subflooring. Some companies also make SIPs with an additional layer, offering interior gypsum wallboard or exterior siding already installed.

Choosing Ingredients

The foam in an SIP can be one of several types, including extruded polystyrene, urethane, and polyisocyanurate. The most commonly used foam is expanded polystyrene (EPS), which is relatively easy and inexpensive to make. All the foams used in SIPs are light and
strong. They keep their shape over time, resist moisture, and do not contain formaldehyde.

 

Although SIPs depend in part on petroleum products, they provide considerable environmental benefits. This is a trade-off that requires accepting one loss to realize another gain.

Features and Advantages

The strength and rigidity of SIPs make them well suited for use in walls, both for their ability to support axial loads (tension or compression bearing on the long axis of a straight structural member) and their resistance to lateral forces, such as strong winds.

Along with strength, SIPs have impressive insulating qualities. Each panel functions as a single structural part. Because the plastic foam core separates the two wood faces, temperature differences between the outside and inside are less likely to be transmitted
through connecting pieces—like traditional 2 × 4 studs. The foam creates a uniform barrier.

Depending on what type of foam is used, an SIP wall provides between R4 and R7 for each inch of thickness. That can translate to more than twice the R-value of a comparable stud wall. An average 2 × 4 stud wall with fiberglass or mineral wool insulation has R-values
of 11 to 15, while an SIP of the same thickness provides R-values of 14 to 25.

In addition to higher R-values per inch of thickness, SIP walls reduce air infiltration. This means even greater benefits for climate control. Even when a research group had two houses built side by side to matching specifications and R-values, the one built with SIPs
consumed about 15 percent less energy for heating. Construction using SIPs is virtually airtight.

Such a well-sealed envelope may not always be desirable, of course. A house with walls made of SIPs may have so little air infiltration that the house may need a fresh-air ventilation or heatrecovery system. As with concerns about airborne environmental
hazards, though, this means the homeowner has more control over what goes through the house. And, with less air flowing through and around the walls, there is also less noise.

Through its Energy Star program, the U.S. Environmental Protection Agency recommends SIPs as energy-efficient building materials.

Using Structural Insulated Panels

Structural insulated panels can help you simplify a project, whether you’re replacing walls, adding on, or building something entirely new. Each panel contains three components in one: structural members, insulation, and sheathing. While SIPs are made in all sizes, most
are 8 feet high and anywhere from 4 to 24 feet wide. The SIPs made for residential construction can be cut at the jobsite and installed by hand with just two people.

Because they take the place of traditional framing members, SIPs must be made to provide at least the same amount of structural support. The panels are created for specific uses, based on the building plans. These plans, some of which are sold by companies that
manufacture SIPs, provide the basis for how the panels are made. The parts are not necessarily interchangeable.

To make sure the panels with cutouts for doors or windows are sufficiently strong, use the panels from a building package that are intended for those purposes. If you cut your own panels on site, make sure you follow the manufacturer’s recommendations. When you
create an opening that is more than 4 feet wide, you will need to add a header. For all openings, plan to install 2× wood framing members along the cut edges. This will also provide a nailing surface and protect the foam insulation.

Manufacturers also provide wiring chases within the panels, so you can run electrical, phone, cable, and network cables without compromising the panel’s strength or insulating properties.

The fire resistance of any structural insulating panel will depend on the wood products and type of foam used. Most national and local building codes provide for SIPs. Some regulations require a thermal barrier, such as 1/2-inch gypsum board, on the interior surface.

This is one area for following the directions exactly. Your goal is to build a structure that is safe and strong. It must meet or exceed the requirements of your local building codes to be financed, insured, inspected, or sold in the future.

Putting It Together

Building with SIPS should be easy and fast. Thanks to their consistent nailing surfaces, you can join wall sections securely. You can also fasten fixtures, siding, cabinets, and so on anywhere you like. Just be sure to buy fasteners intended for use with SIPs. The consistent thickness and density of SIPs also make them less vulnerable to damage, whether it’s accidental or intentional.

Although different manufacturers have their own methods for joining individual panels, two approaches using splines are the most common. In the first method, 2x wood splines are attached between the panels; they function like studs if they are also fastened to bottom
plates and headers. In the second method, the splines are thinner, wider boards that fit in grooves along the edges of each panel. The splines are held in place with adhesives or fasteners, and the seams are sealed with caulk to minimize air infiltration.