SIP it up

Check out the stats on structural insulated panels

Putting up a SIP wall.

Putting up a SIP wall.

Photo courtesy of Todd Harris

Sustainable Space columnists Lori Brown and Greg Kallio are professors in the College of Engineering, Computer Science and Construction Management at Chico State University.

Highly sustainable
If you could design the ideal wall system for your home, what features would it have? The list might include: high R-value, thermal mass, low air infiltration, soundproofing, high structural integrity and longevity, quick to erect, precision-engineered, low environmental impact, locally manufactured materials, and low cost.

Of course, no wall system can be the best in all categories, but the structural insulated panel (SIP) excels in many of them. These systems have been around for more than 50 years and are finally gaining popularity as a smart alternative to conventional stick-framing.

Local pros
While SIP-trained crews are hard to find in some areas, Chico is fortunate to have several local SIP builders, including Todd Harris and Bill Yoskowitz of SIPerior Homes and Robin Trenda of Chico Green Builders. For more technical info on SIPs, you can visit … but first, read on!

SIPs consist of expanded polystyrene (EPS) sandwiched and glued to two structural skins of oriented strand board (OSB). The result is an engineered panel that provides structural framing, insulation and exterior sheathing in a solid, one-piece component that is manufactured in several widths and lengths and used as walls, roofs and floors. Panels are joined together by either OSB “splines” or by dimensional lumber. They arrive precut to the job site and include openings for doors and windows, as well as electrical chases. Brilliant!

Quick turnaround
OSB is composed of recycled wood or new wood derived from lower-grade trees. SIP technology enables builders to construct a high-precision wall system using about 40 percent less lumber than conventional stick-framing. Trained crews can “close in” an SIP home in a matter of days, compared with weeks for a conventionally framed home; this also reduces the possibility of wet-weather damage.

Lots of benefits
EPS offers multiple advantages over fiberglass. The insulating value of walls with fiberglass is compromised by overpacking, movement of air around the fiberglass, and thermal bridging through the studs, joists, plates and headers.

Fiberglass R-19 insulation may provide only R-14 for a 2-by-6, stick-framed whole wall. We know how well a thin-walled Styrofoam (EPS) cup protects our hands from hot coffee. Now consider a 6 1/2-inch SIP wall (5 1/2-inch EPS core) that provides a whole-wall insulation value of approximately R-22! EPS is also a superb sound barrier and is pest resistant due to treatments of borate, a naturally occurring mineral.

Yes, EPS is a plastic that contains petroleum products. This detracts somewhat from its green qualities, but the amount of petroleum is relatively small and the heating/cooling energy saved more than compensates for this fossil-fuel derivative. One manufacturer claims that the average SIP home, in just one year, saves 19 times the energy required to make the EPS insulation. Furthermore, HVAC systems in SIP homes can be downsized by up to 40 percent.

Recap time
In a nutshell, SIPs offer 1) improved energy efficiency due to high R-value and reduced air infiltration, 2) lower on-site labor costs due to fast assembly and erection, 3) lower environmental impact due to a reduction of structural-grade lumber and less on-site waste, and 4) high structural integrity due to their capacity to handle axial, bending, racking and shear loads.

Consider this
To be fair, there are some disadvantages and important differences when building with SIPs: The cost is about 2 percent to 5 percent higher compared with conventional framing (although the increase is offset by reduced labor costs). The use of SIPs requires careful planning so there may be more costs associated with design and engineering. The concrete foundation must be placed precisely to specification to provide a level-bearing surface. On-site panel modifications (and future remodeling) can be more costly. Because SIP homes are more airtight, the builder should give special attention to mechanical ventilation design in order to maintain indoor air quality.