For a vinyl fence to maintain its original upright and inline placement for years to come, it is important to create a stable footing and foundation by installing vinyl posts into concrete.
Soil conditions and exposure to the elements will vary around a property’s perimeter. Although other installation methods may adequately secure the post (such as large rock or compact coarse aggregate) no other method offers the long-term stability of concrete.
Concrete provides a consistent, stable base for your posts. To allow ample concrete coverage around the entire post, 5×5 inch posts should have a 12 inch minimum diameter post hole and 4×4 inch posts should have a 9 inch minimum diameter post hole. The amount of concrete required per post hole will vary based on the type of fence and the load it carries–check with your manufacturer.
Does Concrete Need to be Poured Inside of the Vinyl Post?
End, gate, and corner posts carry additional loads and/or require additional support. Concrete should be filled inside these posts up to just below the top rail and reinforced with ½ inch rebar. An aluminum, or steel support beam can be used instead of concrete/rebar–saving time on installation but adding material cost.
Additionally, due to the extra load and wind resistance of a six foot privacy fence, additional internal support may be required for line posts–especially in high wind corridors. These posts should be filled with concrete and reinforced with ½ inch rebar up to just below the middle rail, or midpoint of the post. I
f you are running the bottom rail to span the length between three posts, consider reinforcing every other post. Aluminum or steel inserts can also be purchased for these line posts and since they only need to be around 50” inches long, generally they are bought at half the cost of the full length inserts.
- Tape the ends of the rails when pouring concrete inside the post to prevent spillage.
- Note, 7-8 foot fences should have all posts installed into concrete.
- Most contractors will not fill any posts with concrete. Instead, where reinforcement is needed, metal sleeves are inserted. Though material costs for the project can greatly increase, the cost of labor can be reduced.
When getting a bid, which I highly recommend, ask to have the cost of post inserts and installation itemized so you can see how much cost it will add to the project. If you choose to go with the bid, you’ll know if you want to tackle post reinforcement separately and/or more affordably with concrete and rebar. - If you are considering installing your own vinyl fence, getting multiple bids will help you itemize labor and material costs, such as: post reinforcement–removing metal bracing from the bid could save around $400 (it is very expensive) and cost you only $50 and a half-day’s labor to do it yourself with concrete and rebar.
Knowing trade-offs like this can help you bring down the cost of a bid into a threshold that is more affordable.
Come on! Really? Concrete in EVERY Hole?!?
Yeah. I get it. Sounds like overkill. It’s just a fence. And it’s not like you’ll be walking or driving on it. But the fact is, installing a vinyl fence is laborious.
Even if your soil is the blackest, richest, fertilest, rocklessiest soil on planet earth’s most chosen remote pasture of solitude. . .Even if your spade just needs a gentle kiss from gravity to penetrate deep into fertile subsurface depths without even the slightest caress from your boot. . .
The fact is, digging a hole 12 inches wide and 30 inches deep is no picnic–even under the most ideal circumstances. And, if the process has to be duplicated 60 more times in order to install all of the posts of your highly anticipated six-foot vinyl privacy fence circumventing your quarter acre lot–it is certain that the job will kick the ass of the studly.
And even the studliest of the studly, after excavating their last hole, will inevitably question, “. . .you sure we gotta cement all these posts?”
Yes, my studliest-of-the-studly friend! You will need to create a strong footing or foundation for your vinyl fence posts…all of them. As long as there is wind, rain, snow, ice, and erosion—or the inevitability of projectiles poorly aimed, a vinyl fence post needs to be anchored in cement. And, in return, it will remain beautiful, squarely erect, plumb, and true for a long, long time.
Concrete and Vinyl Fencing: Generally an Overlooked Aspect of the Project
Whether you are working on a small fence repair, considering a moderate extension, or mounting up for a full DIY vinyl fence install, it will be well worth your time to ensure you understand the suring-up-the-post (concrete) component of the project.
It’s definitely an aspect that is overlooked and, at best, glossed over–as most people don’t even know what to consider, or, what they are not considering–when considering it.
My page on what grade of conrete to use explains more about the different options available to you to help make your decision an easy one.
Why Vinyl Fence Post Installation into Concrete is a Must: Water, Ice and Variable Soil
With the seasons and the elements, there is a lot of expansion and contraction going on in your soil. Believe me, that stuff is alive and is moving around underground. Here are some things to consider.
- WATER: It likes to run downhill and is constantly creating and discovering new drainage routes through your soil–loosening up some areas and tightening up others. This is good and healthy for plants but as you can imagine–just hell for fences.
- ICE: When winter comes, depending on your climate and your region’s frost line, you may have to deal with frozen soil. Frozen soil can swell over 10%.
Not only does the winter’s swelling and contracting cause permanent change to the soil, the changes will not be uniform across your property line–which is unfortunate. We’re talking 2 to 3 inch permanent protrusions and depressions.
Have you ever seen a post that was just two inches out? For a contractor, it’s like fingernails on a chalkboard.
- VARIABLE SOIL: Your property perimeter will accommodate the gambit of different soil conditions–rocky soil, sandy soil, loamy soil, rooty soil, and clay’ee soil.
You might have noticed this in the past if you’ve ever dug out a couple of hollows in your backyard and noticed that one of them was easy and the other left three blisters on your favorite palm.
Seriously, have you ever been digging and then heard the loud clang of shovel-on-rock? It is just hell prying that bastard out–but OHHH so satisfying. However, the thud of shovel-on-clay is my personal least favorite. . . . . .I hate digging through clay. . .I just hate it.
*Side note: I recommend a tow-behind post-hole digger for fence installations.
But, Ehh-hemm! I digress.
All of the different soil conditions accommodate water drainage differently. Subsequently, the earth can get softened up and pushed around in different ways.
Fence Posts Installed without a Consistent Concrete Footing are Subject to the Variable Shifting of Soil
If a fence is installed without a consistent footing or foundation, it will inevitably move with the soil–inways and outways, upways and downways. There is a construction term for this: “skiwampus”–which means, “THAT thing’s a piece of crooked, bent, unsightly, unusable #$%@! Chuck it!” (Excuse my French, I’m just quoting language used on the job-site away from client earshot).
To avoid being that one neighbor with the skiwampus fence, your fence will need a consistent footing as it spans through your property’s jungle of underground diversity. And, concrete, having been around for centuries–fits the bill nicely.
CONSIDER GETTING A BID: Concrete is a Tremendous Amount of Hard Labor
This is a project you will want help with. Do not do it alone. Consider the amount of heft and heave associated with the overall project as you’ll be required to haul potentially tens of thousands of pounds of dirt, concrete, and materials through the course of the installation.
I’ve written a whole blog about things to consider before taking on the project here. It really is back breaking labor and I strongly urge you to obtain multiple quotes from contractors in order for you to be able to perform a proper cost savings analysis by doing it yourself. You may also learn a lot from the local contractors that may help you find ways to make the process more efficient and more affordable.