How deep to set a fence post in Ontario.

The single most common failure on a backyard wood fence in Ontario isn’t the panel. It’s the post. Set a 4×4 an inch too shallow and frost will have it out of plumb by the end of the first winter. Set it right and the posts outlive the panels they hold up.

The Ontario Building Code doesn’t prescribe a single number for residential fence posts, but municipalities default to the frost-depth line for their region. For most of southern Ontario (Toronto, the GTA, Hamilton, Niagara, London), that’s 48 inches. Head north or east and it grows: 54 inches around Peterborough and Kingston, 60 inches around North Bay, Sudbury, and Ottawa. A 10-inch cushion below the frost line is the rule most installers actually follow, which means a 48-inch frost line wants a 58-inch hole.

Post length follows from depth. A 6-foot fence with 48 inches of post in the ground wants a 10-foot post: 48″ buried leaves 72″ above grade to carry the panel. An 8-foot post set that deep leaves only 48″, the height of a 4-foot fence. Where the frost line runs deeper, add the extra depth to the post: a 60-inch frost line and a 6-foot fence want a 12-foot post. Some towns write the depth into the by-law: Richmond Hill requires every fence post to go below the frost line and at least 1.2 m (47 in) into the ground.

Concrete versus gravel is where installers disagree, and both camps are partly right. Concrete is stronger against lateral load (wind, a leaning kid), but it traps water around the post base and accelerates rot on the buried portion. Gravel drains, which keeps the post dry, but offers less resistance to racking. The compromise we specify: 6 inches of ¾-inch clear-crush gravel at the bottom of the hole for drainage, then concrete up to grade, then a slight concrete crown to shed water away from the post. Wrap the buried portion of the post in a moisture barrier (Tyvek tape works, or a bituminous wrap), and the post will outlast the concrete.

A word on concrete: QUIKRETE Fast-Setting is not the answer for fence posts. It sets in 40 minutes, which is great if you’re setting a mailbox, but it doesn’t bond to the aggregate properly and it cracks inside two winters. Use a standard 30 MPa mix, water it in, and walk away for 24 hours before hanging panels.

Post spacing drives panel spec. Our panels are built for 96 inches on centre: that’s the post-to-post distance, not the panel width. An 8-foot panel lives between two posts spaced 96″ apart, with the panel hardware catching a 1½″ reveal on each post face. Build tighter than 96″ and the panel won’t drop in; wider and it sags between.

The last thing nobody tells a first-time installer: set your corner and end posts before anything else, run a string line between them at the top rail height, and set every intermediate post to the string. A 40-foot fence with a ⅜-inch string-line deviation reads crooked from across the yard. A 40-foot fence set by eyeball reads crooked from the kitchen window.

Full install guide is on /installation. It’s the same guide we ship with every pallet.