Footings are the least glamorous concrete on any property and the only part that, done wrong, will systematically destroy everything built on top of it. Here's the mechanism, in plain terms.
What frost heave actually does
When soil freezes, the water in it expands by roughly nine percent. In saturated ground, that expansion has to go somewhere — and it goes up, lifting whatever sits above it.
A footing placed above the frost line gets lifted every time the ground freezes and dropped every time it thaws. Repeat that across a New Jersey winter's freeze-thaw cycles and the structure above is being jacked up and down dozens of times a season.
Why it goes below the frost line
Below frost depth, the soil temperature stays above freezing all winter. The ground down there doesn't expand, so a footing bearing on it doesn't move.
Frost depth varies by municipality across New Jersey, and your township sets the requirement your inspector will check against. It isn't a suggestion, and it isn't somewhere to save money — it's the entire reason the footing exists at that depth.
- Depth is set by local code, and inspectors verify it before the pour
- The trench bottom must reach undisturbed soil, not backfill
- Sloped lots need step footings so every section stays below frost line
- Deck and porch piers follow the same rule as house footings
The symptoms of a shallow footing
Damage from frost heave shows up gradually and gets misdiagnosed constantly. Doors that stick in winter and swing free in summer. Diagonal cracks above door and window openings. A deck that separates from the house a little more each year. Porch columns that no longer sit plumb.
Homeowners often chase these symptoms individually — reframing a door, patching drywall — when the actual cause is a footing moving under the whole assembly.
What a proper footing pour includes
Excavation below frost depth to undisturbed soil, with the trench bottom cleaned rather than left loose. Formwork set square and braced so it doesn't blow out under the weight of wet concrete. Continuous rebar tied through the footing, with dowels placed for any wall going up on top.
Then the pour itself, forms stripped on schedule, and availability for the township inspection. None of it is complicated — it just has to actually be done, every time.