SIPs R-values vary depending on panel thickness and insulating product. Standard EPS SIPs have a nominal R-value ranging from R-4 to R-5 per inch of thickness. Panels made of polyisocyanurate or polyurethane typically cost more and offer a less environmentally prudent alternative, but they also are more fire- and water vapor diffusion–resistant than EPS and have R-values of R-6 to R-7 per inch.
Although some green building advocates object to the use of any petroleum-based building product in ecological construction, SIPA states on its Web site that EPS insulation made of petroleum-derived styrene is actually 98% air. The institute also claims that a SIPs house saves—in its first year—about 19 times the amount of energy required to make the EPS foam used to construct it. EPS foam cores also are recyclable, with some manufacturers accepting scrap material from builders.
“You have to look at the environmental impact of a product over its entire life span,” says Schwind, “with SIPs offering superior energy efficiency over at least 30 years.”
The most environmentally friendly core available today uses recycled waste agricultural straw; however, straw SIPs offer less insulation per inch of thickness, and the panels are considerably heavier, making transportation and jobsite handling a consideration.
The Structural Skin
One environmental concern with SIPs is the presence of formaldehyde in the OSB skins. Although none of the manufacturers we interviewed for this article offer an OSB skin with binders completely free of formaldehyde, some offer alternative skins, such as drywall and cement board. All expressed a preference for OSB as being the most economical and jobsite-resistant cladding. Cement board and drywall are brittle and may break; finished products, such as pine paneling, mar too easily during rough handling.
For those looking for alternative panels, a variety of new materials are available, including light-gauge steel, aluminum, concrete, fiberglass, and a variety of wood panels, such as pine. Some systems offer advantages for particular building needs, especially the cement boards for coastal construction in hurricane-prone areas, where waterproof skins mounted on steel studs offer an advantage over OSB. In the Middle East, SIPs made from a thin layer of Styrofoam sandwiched between about 2 inches of pre-cast concrete have become a popular and economical building material.
Regardless of material, the air tightness of a well-built SIPs structure requires mechanical ventilation to meet most building codes and for common-sense health and safety. With a properly sized and installed passive ventilation system, SIPs will provide an optimum, energy-efficient, structurally superior building system.
Fernando Pages Ruiz builds environmentally friendly, low-cost housing in the Midwest and Mountain States and is the author of Building an Affordable House: Trade Secrets of High Quality, Low Cost Construction and Affordable Remodel.