Air Tightness, Building Materials, Building Performance, Construction Chronology, Insulation, Nauhaus Prototype, Structure, Systems Slab Edge Insulation and Drain October 1, 2009 Clarke Snell Today the foam insulation and drain were installed at the edges of the stem walls, and the CMU was sealed. Click here to view the entire Nauhaus Prototype Construction Chronology. This insulation will serve as a thermal break for the concrete slab. The CMU is sealed to lock out moisture. These ties in the side of the CMU will serve a a mechanical connection to the spray foam insulation.