MontCo Fence Blog

How to Understand (and Accommodate) a Fence Post Depth Chart

The ground beneath your feet isn't a solid, amorphous thing. It contains layers and layers of interlinked systems. Each supports those around it and all of them can move under certain conditions.

All of this subtle rollicking has a profound effect on objects like fence posts. Combating all of this motion is part of why the fence post depth chart was created. It's a set of guidelines that extend the lifecycle of your posts.

Nothing lasts forever, especially not fencing. Water, friction, and hot/cold cycles will break down everything eventually. This is one of the reasons that you find a wide variety of preservatives for wood used in construction. 

Read on to get a better idea of these forces at play under your feet. 

Fence Post Depth Chart Reasoning

Putting a post in the ground is about setting an anchor, not just a point along a line. Footings and braces end up taking a lot of the force of a fence line but the system benefits from the strength of each point.

The weight of your fencing materials is only one force that will be acting against your posts. You'll also be fighting routine weathering and people and animals pushing up against the fence.

Torque and Torsion

The heavier the wind in your area, the more likely you will need your post to have some spring to it. It needs to be deep enough that it won't pull out under heavy wind, but not so deep that it gets unseated by movement in the frost line.

Frost Line

The frost line changes in depth based on your latitude. This is the area of the ground that freezes and stays frozen longer than the ground above it. When the base of your post freezes and the top remains warm, you create condensation which results in water and rot.

Freezing in the ground also constricts the soil. Not unlike popping a pimple, this pushes the post upwards over time.

Ground Water

Groundwater flowing under a post as well as that coming down from rains both work to move your posts. the purpose of backfill and concrete is to diffuse this water and keep it away from eating at your posts for as long as possible.

Keep'n it Level

Since you don't have x-ray vision, you're likely to run into some uneven soil when setting a fence line. Slight rises in the ground and valleys below make it difficult to put every post in at the same height.

You are aiming between 1/3 and 1/2 of the post below ground and the rest visible above. To keep a fence line level, you either need to dig deeper for some posts, while keeping in these parameters, or cut the tops when you have everything set.  

Build Strong

Different soil compositions are going to present different results. You might be in an exceptionally table area and suffer little from a shallow post. The fence post depth charts ifs a guideline, not a rule.

Like so many things in construction, it's better to be safe than sorry. If you have questions about your soil and want recommendations on fencing materials,  contact us.

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