Setting fence posts is a pretty common occurrence around any do-it-yourselfer’s house. But there are a few steps you need to follow to ensure that the posts hold the load they’re intended to hold, and remain solid and functional for years to come.
With fences, you have vertical posts that are supported only by that portion of the post that sits below ground. The post is designed to carry a lateral – side-to-side – load, with no other bracing other than the stringers that connect it to the next post in line. If the post is set too shallow, if the hole is too narrow, or if the soil does not provide firm compaction and support, the post will simply sag over.
First, lay out the line of the posts using a string that is stretched tightly between two stakes. If your property is hilly, or if the run of the fence is quite long, you may need to add intermediate stakes to support the string properly. Lay out the location of each post along the line of the string, and mark it with a stake or a spot of paint.
Digging the holes can be done in most types of soil by using a clamshell posthole digger, which can be purchased or rented. Hold one handle in each hand, drive the edges of the digger into the soil, then spread the handles apart to dig out and grip the soil for removal from the hole. Repeat until the hole of the proper width and depth.
If you have a lot of holes to dig, you might want to consider a two-person gas-powered posthole auger, which can be rented at most rental yards. There are also tractor-mounted posthole augers available for rent, and you also have the option of hiring a company to come out and dig the holes for you.
In most soils, the rule of thumb is that the posthole should have a depth below grade equal to approximately one third of the height of the post above grade. So, for a post that will extend 6 feet above the ground, the hole should be about 2 feet deep. In loose or sandy soil, increase the depth by approximately 50 percent.
In areas that are subject to freezing, the postholes need to extend down past the frost line. Your best bet is to check with your local building department for specific frost-line depths in your area.
The second rule of thumb for post holes is that the diameter of the hole should be approximately twice the size of the post – about 8 inches in diameter for a 4-by-4 square or 4-inch round post, or about 12 inches in diameter for a 6-by-6 or 6-inch round.
In areas of loose soil or high precipitation, place about 2 to 3 inches of gravel in the base of the hole and lightly compact it. This gives a more solid base for the post, and also allows for better drainage.
Next, set a post in each of the corner holes and use a level to check it for plumb in both directions. To hold the post plumb, secure temporary 1-by-4 boards to two adjacent sides of the post and then to stakes driven into the ground.
Secure each of the corner posts in place with concrete. Use a ready-mix sack concrete that you mix with water on-site, and fill the hole at least half full. Allow the concrete to set for at least two days, the fill the remainder of the hole with soil, compacting it around the post. Bring the soil up to about 2 inches above the surrounding grade level, and slope it so that water runs away from the posts.
Remove the temporary bracing, and re-stretch your string between the corner posts. This will help ensure an accurate line for the remaining intermediate posts. Following the same procedure, set up and brace the intermediate posts. Depending on soil and moisture conditions and the length and height of the fence, you can set the intermediate posts in concrete as well, or you can use a mixture of soil and gravel compacted solidly into the hole around the post.
Posts, concrete and all the tools can be found at most home centers, lumberyards and fencing supply retailers.
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