Premier SIPS client Patrick Sughrue of Structures NW LLC explains how to mount solar equipment to a SIP roof in Home Power Magazine: Solar on SIPS
A structural insulated panel (SIP) roof has no embedded lumber in the structure, and therefore nothing substantial for attaching PV array and solar hot water mounts. Single or double lumber splines could be put into the panels, or I-joists at 4-foot intervals could be added. However, the thermal bridging that they would create are at odds with the goal of an energy-efficient building. As buildings get tighter and more insulated, thermal bridging plays a relatively larger role in energy loss.
One solution for mounting solar equipment to a SIP roof is to drill completely through the roof, passing a threaded rod through to the bottom skin and placing a large washer under the nut. Since most SIP roofs are vaulted on the inside, though, few homeowners would be OK with seeing the nuts and washers on their ceilings.
On a recent SIP project in Hood River, Oregon, the PV contractor asked for test results for fastener pull-out so he could design an appropriate rack system. An independent test at Rigging Products in Portland, Oregon, provided the figures he needed. The first test, using hollow-wall anchors, gave a result of 405 pounds to failure. Dividing by three (which accounts for the industry standard safety factor) gives a working load of 135 pounds. Failure occurred as the hollow-wall anchor folded up and pulled through the anchor holes. In an area with 100 mph wind gusts, we did not think a hollow-wall anchor would hold up.
In the second test, two 3/8-inch, high-performance toggle bolts were used. Toggler brand bolts were used with cap screws instead of the original machine screws since the holes in the standoff were 3/8 inch. In hindsight, I would have used 5/16-inch bolts to give a little wiggle room for alignment. In this test, the failure of the SIP—when the OSB skin cracked—occurred at 1,105 pounds, or a working load of 368 pounds.
Patrick Sughrue, Sustainable Building Advisor, has more than 30 years of experience in the construction industry, having been personally involved in myriad aspects of construction from concrete, framing, HVAC and electrical to plumbing and solar. Patrick has been trained in the US Green Building Council’s Leadership in Energy and Environmental Design (LEED) rating system, the Oregon High Performance Home, and the Living Building Challenge, and recently participated in the Passive House certification training. A life-long learner, he also instructs other professionals on green building techniques.
With a personal history of energy conservation and renewable energy projects dating back to the 1970s, including work on BPA’s Hood River Conservation Project in the Columbia Gorge in the 1980s, Patrick Sughrue launched Structures NW in 2003 to assist clients in more easily incorporating a broad range of energy efficient and sustainable products and methods into their construction projects.
Structures NW assists our clients in the design of green building projects. We work with an outstanding team of designers, engineers and manufacturers to provide our clients with the latest in best practices and sustainable green building products. Among those products are structural insulated panels (SIPs) from several manufactures, and Fox Blocks Insulated Concrete Forms (ICF’s), high-performance windows, high recycled-content metal roofing, energy recovery ventilation systems and other accessories.