Foundation CollageWhile these photos might conjure images of fluffy ice cream sandwiches, the high-density foam supporting this concrete slab foundation at Ankeny Row is strong enough to support highway bridges.

What’s the lowdown on the foundation?

The one-foot thick Type II EPS foam creates a “bathtub” in which the concrete for Ankeny Row was poured. Especially fabricated by Insul Foam, the high-density foam continues up the sides of the foundation, eliminating thermal bridging between the concrete and the ground and creating a super-insulated floor.

“Using high-density foam as a structural foundation is not new in the commercial industry,” says Green Hammer’s Dylan Lamar, Ankeny Row’s Passive House consultant. “It’s actually stronger than soil. Type II EPS foam is commonly used as structural fill under highway bridge foundations, for example, but it’s finding new applications in the high-performance residential market.”

Because this technique is becoming common in Passive Houses, we can expect to see it more often in the future, Lamar says.