SIPs below Ground: Comfort Where It's Least Expected PATH Case Study

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With below-grade SIPs, a 5-ply, 2x4 treated glulam functions as the stud, supporting the dirt load against the outside. Composition SIPs are made from a thick layer of foam sandwiched between two layers of oriented strand board (OSB), plywood or fiber cement. For below-grade, Extreme Panels offers 4x8, 4x9, and 4x10 panels with 7-3/8th inches of expanded polystyrene and 5/8 inch of treated plywood on each side. "The key to the below-grade panels is that at every four feet — at every panel joint — there is a 5-ply, 2x4 treated glulam [glued laminated timber]," Stendel says. "That is basically your stud, which serves as a beam supporting the dirt force against the outside. You stand it vertically to carry a load, just like it would carry a load horizontally. "The panels are set on a base of washed rock. This helps address moisture infiltration as the layers of granular rock drain the water away from the below-grade panels. Typically, you want to see at least a foot of washed rock below the floor and wall panels. Panels are sealed with panel sealant and expandable foam, then fastened with stainless steel fasteners. The exterior panel joints are covered with panel seal tape, and the entire exterior is wrapped with two layers of black 6-mil poly. Backfilling is also done with washed rock to provide drainage and decrease the effects of hydraulic pressure typical in heavier soils. " "And while the rest of the structure is conventional OSB panels, we use plywood on basements because you are working with a product that has to be approved for below-grade construction. Plywood has been proven in below-grade applications for a long time through permanent wood foundations. All we have done is taken the permanent wood foundation and turned it into a SIP, just like we have done with stick framing on the upper walls. It's the same concept. "But this inspector needed to be convinced," Stendel says. "He wouldn't approve the plans because of the foundation. The upper panels were all covered by a National Evaluation Report, but the basement panels weren't. "Typically, in a situation like that, we provide research from a Minnesota-certified engineer with a stamp on the plans or a letter attached to the drawings. More often than not, that is usually the end of it. But this inspector just didn't accept that. He said you could put in a permanent wood foundation with stick framing, but you can't use panels in the basement, because he didn't know anything about them." Transportation "The delay pushed the schedule back and made things a little tight," Stendel says. "We were right down to the deadline as to when you could get panels across the frozen lake safely. Extreme Panels delivered the panels at the end of February, but couldn't take their semi across the ice. So the owner actually transported the panels out there himself with a lighter weight truck and trailer." PREVIOUS  1 | 2 | 3 | 4  NEXT