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I would like to repair a Florida wooden fence similar to:

enter image description here

Is there a rule of thumb (ratio) for the amount of post exposed to the amount buried underground? Home Depot has the option for 8,10 & 12 foot posts.

  • Jim Stewart's answer is a general guideline - I can tell you 2 feet under is difficult to remove.. If it were me - I would not use a wood fence in Florida unless I liked replacing it every 4 years. PVC based will last much longer - like 20 years longer and still look really good - the wood fence will rot due to the high humidity and high temperature. Also that fence in the picture is touching the ground - it will draw that moisture and rot .. if using wood keep it off the ground a couple inches. – Ken Sep 28 '17 at 2:39
  • @Ken I agree wood is not a good choice: I neglected to mention that the fence was erected in the late eighties and that two recent hurricanes have snapped the posts – gatorback Oct 1 '17 at 18:57
  • yes as an added advantage to hollow PVC posts - you can pour concrete down the middle (I did) posts have been fine through the hurricanes (100MPH plus) . Fencing on the other hand replaced it once and repaired it another time. – Ken Oct 2 '17 at 22:54
  • do it however you want, but anything less than "all the way down" is insufficient. – tedder42 Oct 6 '17 at 1:49
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I always have used 2' underground so use an 8' post for a 6' fence. I don't know if this would be adequate for a taller fence, but it would probably do at least for an 8' fence.

Once while replacing termite eaten cedar 4x4" posts I encountered a soft limestone 14" or so below ground. I dug 4" or 6" deep into the limestone with a steel digging bar and stopped. I put in the post and then cut 6" or 4" off the top.

  • What region of the world? Did you anchor the post with cement? – gatorback Sep 28 '17 at 12:33
  • You're going to want a 3' hole for a 8' fence in Florida especially because of the high winds you are likely to see from storms and the occasional hurricane/tropical storm. Your area has special roof requirements for high winds, so you don't want to skimp on fences either. – JPhi1618 Sep 28 '17 at 14:27
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    When we moved into our house in Dallas 39 years ago some of the cedar 4x4 posts in concrete were already damaged by termites. I replaced some of them with PT 4x4s 8' long. I got a heavy steel digging bar with a spade on one end, and a tamper on the other, and used it to break up the concrete which I removed with post hole diggers. I filled the holes around the new posts with soil and tamped. I didn't think concrete was necessary with 4x4s in Dallas. – Jim Stewart Sep 28 '17 at 15:37
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    I decided not to use concrete around the 4x4" posts I put in because I thought that eventually I would replace the fence entirely and didn't want to deal with getting concrete out of the ground if I wanted to use the same holes for the posts. In most 'lower end' professional jobs I see they cut the posts off at the ground and put the new posts in different locations. But I was replacing the damaged posts and re-nailing the panels. Also, I wanted to be minimalist--use the least energy consuming materials and procedures that would produce an acceptable result. – Jim Stewart Sep 28 '17 at 18:19
  • @JPhi1618 High winds in FL will not affect the posts as much as the fencing itself. I have posts that have had 100MPH hurricanes and the only issue I have ever had was with the fencing itself. My posts are hollow - 8' - PVC buried (@18 inches) - filled in with about 1' concrete. Posts have made it through with no problems - fencing on the other hand I have had that replaced/repaired twice. After a certain point a big flat fence catching the wind will either snap his 4 x 4's or bend the posts - even steel posts can bend. I have seen large signs with steel posts bent over backwards. – Ken Oct 2 '17 at 22:51
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General rule of thumb is 1/3 the post should be below grade.

  • 4' fence = 2' in the ground
  • 6' fence = 3' in the ground

But it's just a rule of thumb. If you have a 6' fence with an open panel design (ie, not solid) then 2' in the ground is likely just fine.

  • You should proof read your answer - seriously 6' x 1/3 = 2 NOT 3. and 4' x 1/3 = 16 inches. – Ken Oct 2 '17 at 22:41
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    @Ken That's not how you calculate it. The 1/3 is based on the total height of the post--not just the part you see. 9' post with 6' showing (2/3) will have 3' in the ground (1/3) – DA01 Oct 2 '17 at 23:18
  • Actually, after some googling, another way to phrase the rule of thumb is: you want 1/3 - to 1/2 the height above ground to be in the ground. So yea, in general, if you have a 4' fence, you want 16" - 2' in the ground. 6' fence? 2'-3' in the ground. (1/2 the height above ground = 1/3 the total height of the post) – DA01 Oct 3 '17 at 18:57
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This also depends on if you have a frost line. If you do, as in NJ, then your 6' post needs 3' underground for a total of 9'. Trim the excess from the top to level the post. Also, no need for concrete. It just hastens rot due to trapped water. Gravel allows drainage and tight fit.

The spruce rails will rot (if untreated) faster than the posts or pickets.

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