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In a previous issue, I wrote about how to choose foundation systems for buildings, and why higher R-values are justified. This month, we'll compare insulating outside the foundation wall to insulating inside the wall. We'll also look at a new system for placing insulation within a poured wall. Outside Insulation Options The most common exterior insulation is polystyrene foam either in its extruded form (Dow blueboard, Foamular pinkboard, Amoco greenboard, etc.) or as expanded polystyrene (EPS), often called beadboard. The extruded products are about R-5 per inch thickness, and are particularly well-suited to underground applications since they have relatively high compressive strengths, and don't take on any appreciable moisture. One disadvantage of foam is its cost: generally four to five times the cost per R