Q&A / 

Fence Posts

DEAR TIM: What is the preferred method to set fence posts? My 5-foot-tall solid-picket privacy fence has had some issues over the past ten years. The latest problem is posts set in concrete that have snapped. I have installed some temporary steel fence posts to stabilize the fence as winter winds have caused it to lean. How would you install wood fence posts? Should I be using treated fence posts? Ron W., Maumee, OH

DEAR RON: Fence posts can be a real hassle. I have fixed my fair share of them over the years. My guess is there are as many opinions as to the right way to set fence posts as there are posts encircling a one-acre field! But about fifteen years ago, I stumbled upon a method of setting wood fence posts that appears to be working really well.

Your fence posts have a tremendous amount of force against them each time the wind blows. You may not think a 5-foot-tall fence is high, but in terms of wind load, it is substantial. To get an idea of what I am talking about, lift a 4x8 sheet of plywood up and take it outdoors on a windy day. If you are not prepared, the wind may either knock you over or rip the plywood from your hands. Imagine the pressure on the entire fence being held back by a single fence post every 8 feet!

This 4-foot-tall fence post is as straight as the day it was installed. It was not set in concrete.  PHOTO CREDIT: Tim Carter

This 4-foot-tall fence post is as straight as the day it was installed. It was not set in concrete. PHOTO CREDIT: Tim Carter

The average wood fence post seems to be a square timber that is a 4-inch by 4-inch post or possibly a 6-inch by 6-inch post. The surface area of the post in the soil is what determines how quickly a fence will tip in the wind. Smaller fence posts will yield much faster than larger posts assuming both are buried at the same depth.

The trick I discovered is that you can use crushed, angular gravel to trick the wind into thinking a massive fence post is installed. The crushed gravel is affordable and it is easier to deal with than concrete that becomes as solid as a rock. You are about to discover how hard it is to deal with concrete that is deep in the ground around your fence posts. My guess is that you will be swearing like a sailor by the time you get to removing the concrete around your third fence post.

My method of setting fence posts is quite simple. If I am installing a 4x4 wood fence post, I dig a hole 10 inches in diameter. The depth of the hole is important. My tests over the years have shown that the amount of buried post should be half the length that extends above the ground. In your case my guess is your fence posts were taller than the fence, so your wood fence posts should be in the ground at least 3 feet.

When it is time to install the fence post, be sure it is in line with the other posts and it is plumb. It is also important that the fence post is centered in the hole. Start to add the crushed gravel in 5-inch lifts. This means add 5 inches of gravel around the post and use a long heavy 2x4 to tamp and compact the gravel. Each time you are finished tamping the gravel, check to make sure the fence post is still in the correct position.

Continue to install the crushed gravel until it is just a few inches from the top of the hole. You can add top soil to finish off filling the hole in case you want vegetation around the fence post. Some people like the look of gravel, so it can extend to the surface. You can even use a decorative, colored gravel if you like to finish off the hole.

The mass of interlocking gravel acts like an anchor when wind blows against the fence. It also can facilitate drainage of water away from the fence post as the soil moisture drops in late spring and all summer long.

The gravel is also easier to remove than solid concrete in the event you need to work on the fence in the future. A metal spud bar will quickly loosen crushed gravel that has been in the ground for many years.

Fences that are not solid have less wind load against them. A split-rail fence or a regular picket fence that has spaces between the individual pickets allows much of the wind to pass through the fence thus lowering the tipping force. In these instances the fence posts do not have to be buried as deeply.

If you decide to use treated fence posts, be sure to use the proper timbers. Not all treated lumber is approved for burial in the ground. The treated fence posts should be labeled that they are approved for direct burial.

Always be sure to call the national Call-Before-You-Dig Number a few days before you start your fence project. Simply dial 811 or go to their website www.call811.com. You may prevent death, serious injury or substantial expense by doing this. You would not be the first person to strike an electric line, phone line or even a buried natural gas line with a posthole digger!

Column 713

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18 Responses to Fence Posts

  1. Tim,

    I was bouncing around the web looking for the best method to set wood fence post and found this comment. I live in Oklahoma where the winds
    Can get pretty strong and actually just snapped my neighbors posts. I am building a 6' privacy with little to know space between planks. Is this method you are using good for this or should I dry pack with concrete? I would
    Really like your opinion.

  2. Can we put a fence up over a drain field? Septic tank itself is right outside the back porch. What would you suggest? Will it be harmful for the dogs to be out there?

  3. I live in illinois, on a hill. winds are not too bad but can get pretty gusty at times as i live just off the mississippi. I want to put a Easy Gardener 7 ft. tall. DeerBlock Protective Mesh around my garden, and was planning on using 4x4x10' posts for this fencing. it is aproximately a 20' square garden and plon on myabe 8 posts. How deep should i sink the posts and would this be effective enough and enough poles for this style fencing? Or do you think wooden poles would be over kill?

  4. Good article Tim, thinking about doing this myself and wondering if you have any recommendations on what size crushed gravel to use, or does it matter? Thanks!

  5. Tim, I want to install a volleyball net over my above ground swimming pool. I live near Chicago so we get every sort of weather. My ground is clay after a foot or so. I bought 2 6"X6"X14' PT postsand plan on renting a hole auger and going 4' or as deep as I can get it. Once the net is installed it will try to pull the two poles in towrds themselves so I was thinking about pouring another concrete footing about 6' away from the poles to attach guy lines. My fear is that if these posts rot they may fall in on the pool and collapse the whole thing. The guy lines are also insurance for this - they would pull the posts in the opposite direction of the pool. What is the best way to set these posts? They need tol be stable and remain straight. Thanks, Brian.

  6. I am constructing a 6ft privacy fence, and on one side I have encountered a problem with a hole right in the middle of the fence line. The hole has water seeping up from the bottom. We have bailed out the hole, but water continues to seep in. What can we do to fix this, or can it be fixed at all?

  7. Tim, thanks so much for just reading my question, It's my hope you can/will advice me in building my fence. I lived in Mississippi and I purchased my home over twenty years ago and I think I've had to replace or repair my privacy cedar fence if not every year, at least every other year as I'm close to the Gulf Coast and we get those one-hundred and thirty-five mph wind as in Katrina. This time I'm installing treated pine 6"x6"x10' post 72 inches apart on center and using a concrete tube 48 inches in length 12 inches in diameter and putting them 42 inches in the ground and letting 6" rise above ground level and hopefully preventing the post from ever rottening over time. I'm putting four and half bags of 80 lbs 5000 psi concrete in each hole, as well as using four runners 2" x 6" x6 feet, my pickets are cedar 51/2 inches in width and 84 inches high as I raised them off the ground four inches in hope the weed trimmer or rain water level won't distory them as well. Do you think this fence will withstand hurricane force winds and if not what should I do different, please.
    Respectfully,
    Harwell

  8. I'm replacing an existing fence in south Florida . The ground is some type of coral with about 2 inches of top soil . It's a wooden fence and the cement has bonded with the coral preventing me from digging around the cement and pulling the post out .what is the best way to remove the posts? What equipment is needed? Do I need a tractor to pull out the posts?

  9. Hello Tim.
    I would like to put up some 4'x8' sections of privacy lattice (lengthwise across) since I live in an HOA with houses very close together with NO privacy. When I voiced my concern to my realtor she said to just "plant it out." Well, I found out that is not possible as the soil is clay and the drainage is terrible! My two neighbor's gutters and downspouts drain into my front mini yard and my backyard (and they refuse to correct the problem) -so even though I had 2 French drains put in the back which was quite costly, the water still pools and stands, so nothing will grow there. I cannot plant trees as the distance of my yard to the neighbors' houses is very narow and quite close. I'd also like to do something that will work now in my immediate lifetime. My idea is to put a row of 4-8' lattice panels end to end on 4x4 treated fence posts length-wise across three sections of my yard and then plant some kind of evergreen vine at the ends perhaps on a berm or raised brick flower box. The lattice can be 8 ft. high (as a "trellis") but cannot be attached to the (very decrepit) fence as fences can only be 6 ft. tall. I got HOA permission for the 8' trellis. SO! My big concern is putting fence posts in a swampy area, which is often since I live in Vancouver, WA where it rains a lot. I am a senior on very limited income so can't afford to hire a company to do the project. After 5 years my son has finally said that he and his visiting friend from out of state will do the job, but I know he prefers to cut corners and do it quickly. He wants to put the 10 ft. posts 2 ft. down in quick-set concrete and slap the lattice panels up. I fear the posts will rot out quickly in this soil and climate and have also been told that the lattice panels (cedar) should be painted with clear penetrating sealer before installing. I don't think either of them plan to stick around long enough to do that. I'm 71 and 5' tall so can't do it after they are up, and could not get to the other side to paint it. "Time" is a huge factor before his friend leaves, and my son goes back to work. I have spent several hours reading about fence posts online, (finding so much contradiction) and it seems to me that it may be best to not have the posts in the ground at all, but to have them sit above ground level on a metal post support that is itself sunk into the cement. Cost is a huge factor for me, and I looked at all kinds of metal supports and spikes on line, and would very much like to have your professional opinion on the best way to go about this project, and in the most economical way that will last. I do hope it will be possible to hear back from you very soon as I think there is little time to corral my son and his friend (before he leaves) to do this job for me.
    Best,
    Cheri

  10. I live in Toronto and the frost line last year was 4 1/2 feet. I am going to use 6 x 6 x 10' posts and I'm going to cement them in the ground 4 feet with a 10 or 12 inch Sono tube. I want the fence to be 6 feet high .Do you think that will be sufficient? Thanks for your time.

  11. I'm building a 6-ft-high lattice-topped cedar fence. The basic 8-ft-wide panels are solid. Instead of setting the 10 panels close to the ground as is usually done, wouldn't it be better wind-wise to place them, say, 6 inches off the ground, giving the wind a place to pass through? Rabbits and other flora-eating varmints will have easy access, of course, but they can get through via about 200 ft. of open lawn anyway. Thanks.

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