It looked easy enough: Stack a bunch of hollowed-out lightweight polystyrene blocks, fill the cavities with concrete, and presto! — an insulated foundation, ready for interior finishes. I was taken by the technology: With insulated concrete forms (ICFs), I would have a high-tech foundation. I quickly realized, however, that I had a lot to learn about working with ICFs.

I had already built an ICF frost wall for a new entry porch on an old farmhouse. Although the concrete foundation didn't need to be insulated, the ICF blocks were easy to stack, and it was a simple matter to cut the blocks to fit around the existing rubble stone foundation. Once they were laid up, I backfilled on both sides and poured concrete...

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