So you’re ready to build a fence. You’ve planned the layout, picked your materials marked out your property lines and all underground utility lines and are ready to start building!
Step one, and arguably the most important step is setting out all your fence posts. Posts provide the base, support and strength for the entire fence. Generally speaking, posts are spaced six to eight feet apart and you will want to make sure they are level with each other.
But what about the depth you ask? How deep does my fence post need to be? Read on to find out more…
How Should I Dig My Post Holes?
Before we explore post holes, the frost line, the ground conditions and so on, we need to establish the best way to actually dig the perfect post hole.
You may be thinking to yourself, “There’s no shortage of ways to dig your holes” and you’d be right. However, we suggest using the right tools for the job. The best tools are hole auger or post hole digger (known as a clamshell). Using a conventional shovel will create flat-walled, barrel-shaped holes that aren’t ideally suited to accommodate posts. Especially here in Canada, you will also need to ensure that the posts are set beneath the frost line to prevent heaving.
If I had a dollar for the number of times we’ve seen fences that aren’t level, a post out of line, one hole deeper than another and various other mishaps.
Should Fence Posts Be Set In Concrete?
The simple answer to these questions is yes! Concrete is the most secure material when it comes to setting fence posts, especially if you have sandy soil. Other materials such as gravel may be suitable when the ground is predominantly dense, heavy clay, but is looser soil, concrete is the way to go.
Pro Tip: Although concrete is extremely sturdy it lacks the drainage qualities of gravel. This will ultimately result in an increased amount of moisture, leading to rot. To combat this, when you pour your concrete, fill the hole so that the top of your concrete forms a dome shape. This will allow for runoff, directing the water away from the base of your post.
Is 2-Feet Deep Enough For Fence Posts?
We’ve established that spacing is extremely important, but what about the depth of your post holes. A common question we receive is “Is 2 ft (24 Inches) deep enough for posts”. The answer to this question will depend on the project you are taking on. There are times where the height may not exceed 6ft. In these cases, the post hole doesn’t have to be as deep as it would for a 6ft and above the fence.
Anything less than 24 inches will put your fence at risk of blowing over in adverse weather conditions. Remember, these are wood posts that have been set in concrete, if your fence post isn’t deep enough, it is prone to snapping and collapsing all of your hard work.
Is 3-Feet Deep Enough For Fence Posts?
As mentioned before, the depth you must dig for your fence post should always depend on the size of the fence you are building. As a general rule of thumb one-third of your post should be underground, the other two-thirds above. Let’s take a standard 6foot (72 inches) fence as an example. You will need a 9foot (108 Inches) post so that 3ft (35 inches) can be underground and 6ft can be above ground.
As always, make sure the hole is dug to accommodate the post you are using to support the structure. you will want to have nice level posts that have been set in concrete. Having the concrete set in the dome formation will ensure that less moisture will be retained.
So...What Did We Learn?
When it comes to building a fence the depth of the post will depend on the size of the fence you are building. It’s recommended that you dig your hole with the correct tools so that your wood post sits snug within that space.
Depending on the ground you are looking to construct the fence on, you may need to assess the situation to select materials that will work with your site. It is very common for wood posts to have water damage because the builder didn’t take into account where the frost line is, or setting the posts to allow for drainage.
Ensure that your post is one-third below the ground and two-thirds above. This will ensure you have factored in the frost line and provide a sturdy base for the security of the fence.