You’ve probably seen those gigantic pile drives hammering huge, wooden posts down into the ground and wondered if something similar could be done in your own backyard. Maybe you’re considering building a deck or getting ready to lay the foundations for an extension on your home, or a separate garage/shop.
You can bury your own deck posts as well. Perhaps not with a giant rig designed for driving it in the ground. You’ll certainly have to dig yourself quite the hole to get your post deep into the ground. It’s a terrific idea for creating the building blocks for a foundation, at least on paper.
Its probably not something that you would necessarily need to do if you have your own personal designs on a deck, however, from the perspective of laying down a permanent and long-lasting structural support and foundation, it seems like a pretty good idea.
Unfortunately, the idea also comes with caveats, both in terms of necessity and longevity.
Pros and Cons of Burying Deck Posts
The practice is often seen out on the beach, prior to small condos going up. The contractors will bring out a large, crane-like machine that lines up large piers in a vertical position.
The machine is equipped with a retractable, steel (sledgehammer) that will raise up and drop onto the top of the pier, driving it down into the ground. You can do something similar in your backyard, just without the massive crane.
The idea behind several, underground posts is to build your framework on top of it, feeling comfortable in the idea that your support is deeply buried and stabilized within the earth. And on its face, this is very true and it will be a very effective, stabilizing force.
However, even if you treat your posts to resist water, rot, and decay, it won’t matter. Constant exposure to the moisture of the earth beneath, with no air circulation to allow the post to dry, it will rot out from underneath you and it will do so in a hurry.
When burying a post, there is usually an amount of concrete involved as the “footing” of the support anchor, with the vast majority of the post insulated in gravel or a preferred aggregate that keeps the dirt off of the post.
The problem is, the aggregate doesn’t keep moisture off of the post and it will eventually begin to rot in the ground. Once the rot or decay takes hold, its a fairly rapid process after that.
| Pros | Cons |
| Immediate and effective, stabilizing anchor/forceEasy to installEasy to build a framework on | You can’t prevent or avoid rot and decayLoses stability over time |
Better Methods for Installing Deck Posts in the Ground
The idea behind burying a post to provide a powerful and lasting foundation is nothing new and it generally works pretty well, however, if the wood (even if treated) is exposed to the elements underground, without air exposure to allow it to properly dry, it will rot.
The “post in concrete footing” is the traditional method that most people use when they are building a deck or other, similar structures.
Post in Concrete Footing
When you are using this method, you should bury the post to a length that is ⅓ of the length of the exposed post. For instance, if 6’ of your post will be above ground, then you will need an 8’ post with 2’ of it buried in the ground.
When you dig your hole for the post, it should be three times the width of the post. Most posts that are used in residential projects are 4” x 4” posts, so your hole should be a solid foot in diameter.
Build a framework that you can carry around to each post as you install it. The framework is a simple ring or square that you will lay around your post so that your concrete pour is a shade above the ground, rather than being flush.
You want to avoid water pooling up around the base of the post, and pouring your concrete up, above level will help create a little bubble for runoff. Use a long stick or a piece of rebar to agitate the concrete by poking it at least twelve inches down into the concrete over and over.
You should do this 25 times, as it will remove all of the air pockets caught between the post and the concrete, increasing the overall stability of the structure.
Pier Method
You’re essentially pouring cubes in the ground with a section, maybe three inches or so, sticking out of the ground. This section will connect with your 4 x 4 post via an anchor and the braces will need to be exceedingly strong, as this type of foundation is susceptible to lateral weakness.
A bit of overkill is called for and your concrete cubes should be about 20” x 20”, which is more than enough to provide a stable pier for you to anchor your 4 x 4 posts. Once the concrete is adequately cured, you can go about installing your 4 x 4 posts.
This method is one of the most stable, up and down, stabilizing forces available at the residential level. It keeps your posts well away from the ground. So, while you won’t have to worry about your posts rotting, you still need to use only treated wood.
In terms of lateral support, bracing your posts on top of concrete piers doesn’t provide much in the way of lateral stability, so you will want to build in some side-to-side support as well. Or, you could use concrete footings on your perimeter posts and piers on the interior.
Final Thoughts
You can certainly bury your posts in the ground and use them as a foundational material, however, you should never do it in a way that exposes the wood underground. Without proper air circulation, your post will rot, regardless of how well it is treated.
There are other ways to design a foundational system that protects your stabilizing materials from rot and you should use them if you decide that you want to build a deck or lay down a supporting structure for something much larger.
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