How Deep Should Fence Posts Be in Ontario? The Frost Line Rule

The most common reason a fence looks wavy after a few years is not the wood or the panels — it's the post depth. In Ottawa and surrounding areas, frost heave moves anything shallow upward. A post set too short will push out of the ground, tilt the panel, and eventually ruin the gate.

The 4-foot rule

Most of the Ottawa area sits in a frost depth zone that requires posts to be buried roughly 4 feet deep for a 6-foot fence. Taller fences, heavier gates, or clay-heavy soils need more. We dig by hand or auger to depth, tamp the base, and pour concrete so the post is locked below the active frost layer.

Why concrete matters

A post packed in dry soil or gravel can shift. Concrete around the base forms a footing that resists uplift and keeps the post plumb. We slope the top of the concrete away from the post so water runs off instead of pooling against the wood.

Gates need extra care

A gate is the heaviest, most-used part of a fence. Gate posts should be larger — typically 4x4 or 6x6 depending on the gate — and set deeper than line posts, with extra concrete and diagonal bracing built into the gate itself. A sagging gate is almost always a post problem, not a gate problem.

We install fences across Barrhaven, Kanata, Orléans, Nepean and the surrounding Ottawa area with posts set to local conditions. If you're comparing quotes, ask specifically how deep the posts will be set and whether concrete is included.