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Out of Sight, NOT Out of Mind Specifying thermal insulation below-grade and under-slab by Ram Mayilvahanan All photos courtesy Insulfoam IN THE PUSH TO FORGE MORE ENERGY-PRUDENT BUILDINGS, DESIGN PROFESSIONALS ARE LEAVING NO PART OF THE ENVELOPE UNEXAMINED. WALLS AND ROOFS HAVE ALWAYS PRESENTED A CLEAR TARGET FOR BETTER THERMAL PERFORMANCE. SOMEWHAT LESS OBVIOUS ARE SURFACES THAT ARE OUT OF SIGHT—BELOW-GRADE FOUNDATION WALLS AND FLOOR SLABS. WELL-ENGINEERED INSULATION IN THESE LOCATIONS CAN PROVIDE SIGNIFICANT ENERGY SAVINGS. What separates below-grade insulation types from one another? Moisture retention, R-value stability, and compressive strength are the key performance attributes to consider when evaluating and comparing different below-grade insulations. Installing thermal insulation on below-grade foundation or perimeter walls and under slabs is important because un- insulated concrete provides a thermal and moisture bridge between the heated building interior and the relatively cooler earth surrounding the building, or through exposed slab edges to the outside air. 34 the construction specifier | december 2013 CS_DECEMBER_2013.indd 34 2013-11-14 2:39 PM