Innovative Insulated Panels

Enlarge Image Image Gallery SIPs can support loads of many thousands of pounds. STEVE MAXWELL

Among the many breakthroughs in building materials and home construction, structural insulated panels (SIPs) are one of the best. SIPs are rigid foam sandwiched between factory-bonded oriented strand board (OSB). Panels are usually 4 to 8 feet wide and up to 24 feet long, and can be used for walls as well as structural roof sections.

They’re simpler to erect than stud- or timber-frame walls, which means they go up faster, too. But the real benefits of SIPs are their strength — twice as strong as a stud wall — and energy efficiency; insulation values typically range from R-15 to R-45 (stick-frame insulation is about R-12 to R-20), depending on panel thickness and the type of foam core. SIPs increase the total building cost by only 1 percent to 3 percent, and labor and energy savings quickly offset the added expense. A study by Brock University in Ontario showed that, over the course of a year, one home with SIPs used only a quarter of the energy consumed by an adjacent stick-frame house with an identical floor plan (for more about this study, see “The Inconsistency of R-values,” below).

“SIPs have some tremendous advantages in terms of energy performance,” says Alex Wilson, executive editor of Environmental Building News. “They create a tight, well-insulated building shell that doesn’t have the thermal bridges that result from wood studs in conventional construction — and they do this with efficient use of resources.”

I’ve built structures with timbers, logs, stone and studs, and my experiences with SIPs have impressed me enough that I’ll use them again. When I chose SIPs for my latest building project — a 1,300-square-foot, two-story workshop — I knew I was heading into new construction territory. (Read about Maxwell’s workshop in A Blueprint for Better Building, August/September 2005. — Mother) But learning to build with this material proved easy, with results that were stronger and more energy efficient than I was expecting. The structure also went up more than three times faster than a stud-frame equivalent — even though I was working mostly alone. Before I even had heat in the place this past winter, indoor temperatures regularly climbed above freezing on days that were below zero outdoors, despite cloudy skies.

BUILDING WALLS AND CORNERS

You can order precut panels for an entire home — or you can cut the panels to create door and window openings after they are delivered to the building site. Some companies even offer panels with interior or exterior finished surfaces. To make walls, simply tilt the panels upright one at a time. The panel edges are shaped to allow joint connectors called “splines” to lock adjoining panels together. SIPs also are made so that 2-by-4s and 2-by-6s can be installed in the recessed edges around door and window openings. When you’re done, all you see is OSB on the inside and outside faces of the walls.