How Deep to Dig Fence Holes

Answer: The frost line in Ottawa is 3.5 to 4 ft deep, and we recommend digging to a depth of 4 ft for fences in Ottawa. This will also be stable for a 7 ft fence height.

When installing a fence, it's important to make sure your fence posts are buried deep enough to withstand the harsh winters and be stable structurally. The depth will depend on a few factors, including the type of soil you're working with, the height of your fence, and the frost depth in your area.

There are 2 major considerations for how deep your fence post needs to be:

• Going Deep enough to go below the frost line

• Digging deep enough for structural stability and strength

Frost Depth

Frost depth refers to how deep the ground freezes during the winter months. In Ottawa, the frost depth can range from 3.5-4 feet deep. When the ground freezes, it can cause the soil to expand and push upwards, resulting in what's known as frost heave. This can cause fence posts to shift or even lift out of the ground if they are not deep enough. The force exerted by frost is tremendous and can be enough to even shift house foundations.

In addition to going deep enough, its is beneficial to “bell” out the bottom of the hole so that the concrete can resist the upward force of the frost heave.

In this example, the hole is “belled”, but the hole does not go below the frost line. In time this post would heave upwards.

What are the effects of your posts lifting up?

• A weaker fence since the burial depth is being reduced as the post comes up and the concrete starts to crack.

• Alignment issues, your fence lines will no longer be level, and some panels may start leaning

• Broken connections as some panels lift up and others don’t.

Structural Stability

The depth of the hole may need to be adjusted depending on the height of your fence in order resist wind forces. Generally speaking, the fence should be at least half as deep as it is tall.

A 6 ft tall fence would need to be at least 3 ft in the ground to provide structural support. A 7 ft high fence would need 3.5 ft.

All our fence holes go down to a depth of 3.5 to 4ft which ensures they are deep enough to withstand frost heave and be structurally stable.