Over the past few years, we have both had the opportunity to try Sparfil Block—the heavily insulated concrete block developed in Canada. Unlike other insulated block systems, Sparfil does not achieve its outstanding R-value simply by using foam inserts in a modified block. Foam inserts improve the R-value of block foundations, but the effectiveness of this approach is usually limited by two factors. One is that there is only so much of the block that can be removed to make room for the insulation before the block becomes too weak and fragile. The remaining block presents a significant thermal break. The second limitation is the mortar joints. Even if the R-value of the blocks is raised, the 3/8-inch mortar line
