Steel ducts make great footing forms. I save steel HVAC ducts, both the leftover pieces from a new installation and old ducts removed during a system replacement. Then, rather than buying cardboard tubes for footing forms, I duct-tape short pieces together to reach the local 42-in. frost depth. Round ducts work best because they don’t collapse when backfilled, but even square ducts can be used as forms provided I brace the insides every 16 in. or so. Small-diameter scrap pieces of PVC pipe or electrical conduit make good braces, and 1×2 strips of pressure-treated lumber scraps work as well. The great thing about these steel footing tubes is they’re not affected by damp soil or rain that can cave in cardboard tubes. I’ve used them to form grade-beam piers, footings for decks and sheds, and pier anchors for plastic-covered greenhouse frames.
Mike Guertin, East Greenwich, RI
Edited and Illustrated by Charles Miller
From Fine Homebuilding #216
