How do I avoid winter frost heaving if my cottage is on piers?

My cottage is on piers. How do I avoid winter frost heaving?
—M.T., Parry Sound, Ont.

Frost heaving—when moisture deep in the soil freezes into chunks (called ice lenses) and then exerts pressure on the piers—is more likely if the piers are in fine-grained or poorly draining soil, so adding granular backfill, and increasing the drainage, can certainly help. To keep the soil warmer and prevent frost from penetrating, lay down a 5-cm thick layer of rigid foam insulation underneath the cottage, fitted snugly around the piers. You’ll want to put the insulation roughly 15 cm below the ground, and anchor it with gravel or coarse sand. You can do this yourself, but it’ll involve quite a bit of shovelling and crawling around on hands and knees. Hiring a contractor to jack up the cottage to access the ground with an excavator would be easier on your joints (but much harder on your wallet).