04/23/2026
Michigan's frost line sits at 42 inches. That's the depth the ground reliably freezes to in a bad winter in Metro Detroit. When water in the soil freezes, it expands. That expansion pushes upward — it's called frost heave, and it doesn't care what's in its way.
A post set at 24 or 30 inches sits right in the middle of that freeze zone. First winter, maybe nothing obvious. Second winter, the post has moved a quarter inch. Third winter, you're starting to notice the fence isn't quite plumb anymore. By year five, the post is visibly leaning and the panels are starting to rack.
The fence didn't fail. The installation failed. Two different things, and only one of them shows up in the warranty conversation.
What makes it worse in this area specifically is the soil. Metro Detroit sits on mostly heavy clay with few exceptions. Clay holds moisture better than sandy soil, which means it has more water available to freeze, which means the heave forces are higher than they'd be in a drier region. 42 inches here isn't conservative — it's the floor.
The other thing worth knowing: a post that's heaved once is easier to heave again. The freeze cycle loosens the soil around the post. Each cycle after that takes less force. So the fence that looked fine for three years can go from "slightly off" to "noticeably leaning" in a single bad winter.
Post depth isn't a line item you negotiate. It's the part of the job that determines whether everything else holds.
