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Community and Q&A

Is it possible to build a floating fence?

PLIERS | Posted in General Questions on

Hey hope everyone is doing well. I planted hemlocks about 5 years ago for privacy in my small yard. The hemlocks have grown but they take up a considerable amount of space and not crazy about the look. Thinking about removing them and placing a privacy fence and gaining some of that space back. My issue is that I want to get the most space possible but the edge of my yard sits on an old stone wall. It is literally stocked up rocks so digging posts may disrupt the old wall. I’m trying to find a solution with less disruption. Can you build a floating fence using concrete deck posts? I have seen decks built on it. My other thought is building some kind of small block or brick wall and just stack it or build the fence on top of it somehow. Just looking for some ideas.

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  1. Expert Member
    Michael Maines | | #1

    A traditional way to build fences was to set rot-resistant posts in the stone wall itself. Privacy fences experience significant lateral loading from wind so they need to be well-anchored. You might consider helical metal piles for posts:

  2. Expert Member
    DCcontrarian | | #2

    It's all about the lateral loads and there are two ways to address that -- go deep or go wide. Neither one is easy with a stone wall right there.

    I disagree about the helicals, they have poor lateral resistance unless you can tie them together.

    1. Expert Member
      Michael Maines | | #3

      They are exactly the same as any fence post, except for the surface area in contact with the soil, which is what resists lateral loads. Fence posts buried in concrete have greater lateral resistance because the concrete has more surface area pushing against the soil. (I know that you know that already.)

      If you have soft soil, such that posts set in concrete would be vulnerable to tipping, then helical piles probably wouldn't work. If you have bedrock close to the surface they won't work at all. But if you have a soil with good bearing capacity, they work just fine as fencing, though you might need more posts than you would if they were set in concrete. The OP stated that digging post-holes wasn't an option.

      As I recall, you have found them to be expensive; that's not the case here or in many places but it seems to vary quite a bit.

      1. Expert Member
        DCcontrarian | | #5

        I don't see helical piers giving any better lateral resistance than a metal post driven into the ground. Probably worse because the helix disturbs the earth on its way down, whereas a driven post doesn't.

        And yeah, I paid a little over a thousand bucks a pier for my project.

        I'd recommend driven posts. The problem is that places where stone walls are common usually have such rocky soil that post driving isn't productive.

        1. Expert Member
          Michael Maines | | #9

          Yes the lateral resistance would be essentially the same as a steel post driven directly into the ground. A post set in a 6" concrete Sonotube would have twice the lateral resistance of a 3" diameter steel post on its own; doubling the number of posts would result in the same lateral resistance. You're probably right that the augur loosens the soil a bit but from the installations I've seen and worked with it's not a big difference. (I'm almost done with the addition pictured in this article: and even without diagonal bracing in place the piers have been very stable.) Helical piers wouldn't be my first choice for a fencing system and you're right about rocky soil.

          I've never seen metal fence posts driven into the ground, is that a thing? I've seen farmers do it with wooden pasture posts and I know pile-drivers who do major projects, but I haven't seen metal fence posts installed that way.

          1. Expert Member
            DCcontrarian | | #11

            It must be regional, in DC it's the norm to drive chain link fence posts in the middle of runs, corners and ends get set in concrete. We have a red clay that is very solid.

            The problem with doing any sort of calculations for fence posts is that the loads are lateral and really hard to estimate. The lateral bearing capacity of soil varies tremendously. The main lateral load is wind, and that's going to be hard to estimate too because you're right against the ground.

            In 2016 I put up a 30x96 greenhouse (this model: ) that was supported entirely by 50 pieces of 2" chain link fence post. Each piece was driven 30" into the ground. It's still standing. The posts were driven with a hand-held post driver, and where the ground was particularly hard a sledge hammer. That was a fool's job!

          2. Expert Member
            Michael Maines | | #19

            It might be a thing here too; I have some funny blind spots in my experience, such as never having chain link fencing installed on any job that I can recall. I have taken some out that was set in concrete.

            That's quite a greenhouse. I've driven enough T-posts on my small farm and installing traffic signs that I have a decent idea what setting 50 fence posts would feel like. Your shoulders were probably not happy with you!

          3. Expert Member
            DCcontrarian | | #21

            Yeah, the hand held post drivers are the tools of ignorance. I've done a lot of t-posts and the round posts were a lot worse.

  3. PLIERS | | #4

    There is space next to the current retaining wall. It’s about a 1-2 foot deep drop off. I have to measure. I’m thinking of building a narrow retaining wall behind the old one. Then if I disrupt the soil or the stone in the original retaining wall it will not collapse when digging for the new fence. The original retaining wall I’m assuming would be enough drainage behind new one saving me an extra step.

  4. maine_tyler | | #6

    It's a bit hard to know exactly the situation you are describing. Your yard is on the up-side of a retaining wall? And the retaining wall is a rubble style, with stones in the way of where you would need to dig for a post? A post hole needn't be very wide at all.

    Without really knowing... two random thoughts:

    ‣Zig-zag fence--
    ‣Some sort of deadman.

    Or trim the hemlocks.

  5. Expert Member
    BILL WICHERS | | #7

    You could also try a varition on the serpentine wall:

    Note that if the stones are large enough, you can drill holes in and set anchors to hold up posts.


    1. Expert Member
      MALCOLM TAYLOR | | #8


      Have you seen Andy Goldsworthy's walls?

      1. Expert Member
        BILL WICHERS | | #15

        Very Frank Lloyd Wright-y!

        I like how the curves are randomized too -- usually you see very even patterns. Sometimes random is more interesting visually.


      2. ohioandy | | #16

        Why don't I have time in my life to do this?

      3. StephenSheehy | | #20

        Storm King is not to be missed!

  6. PLIERS | | #10

    Here is what I’m working with, with some pictures, I have pictures of the side and the back. First 2 are side followed by back of property. There are old steel poles from an old fence in the concrete on the back wall.. As you can see the trees take up a lot of space. I have neighbors to my right and commercial buildings in the back. Trying to build a 6 foot fence in most economical way without too much disruption. The concrete is wall is old so don’t want to disrupt it too much.

    1. Expert Member
      DCcontrarian | | #12

      Is the concrete on your property? Are those posts solid? I'd use the existing posts, maybe sleeve them to dress them up.

      If the concrete can support a fence, you can rent a core drill that will make 1-1/2" or 2" holes and put posts in it.

      1. PLIERS | | #13

        So I could make holes in a 4x4 and then place on top of metal posts to build a fence? I was also thinking of maybe using those premade vinyl fences as well, slipping them on as you said if the spacing is right. Is wood easier here?

        1. Expert Member
          DCcontrarian | | #14

          It's really hard to drill a long narrow hole like that. What is done fairly commonly is building a box out of four pieces of wood and assembling it around the pole.

          1. Expert Member
            Akos | | #17

            +1 Exactly what I was thinking.

            For the rubble section, there is no easy way. Remove the stone in a 12" section and dig a hole for a post, re-stack the stones around the new post. One thing you can do is only dig down for every 2nd post. If you tie the top of 3 posts together with a long piece of lumber, the middle one is now supported and can simply rest on the ground in a saddle.

    2. PLIERS | | #22

      How should I build the fence on side that is extremely close to my neighbor. I’m assuming I need the fence to be far enough I can walk in between both fences without giving up too much space. Especially since I will be nailing the pickets on the back side of fence. If only my neighbors fence was higher I wouldn’t need to build one next to his.

      1. Expert Member
        DCcontrarian | | #23

        Where's the property line?

        1. PLIERS | | #24

          Looking at the survey looks like the fence is on the property line or so close that it looks like it’s on the line. Idk how weird this would look but I can fence the back side of property that sits on a retaining wall because I have a few feet of property on that side. Then the side that is super close to my neighbor I can’t plant a more narrow tree, well anything more narrow than the hemlocks I have now. Can I sell these trees to a nursery or is it easier just to remove them.

      2. Expert Member
        DCcontrarian | | #25

        Have you thought about offering to pay the neighbor to put in a taller fence?

  7. PLIERS | | #18

    That could work, dig down for only every 2nd post. What spacing are we talking about 4 feet posts with a 8 foot long lumber to tie it?

    1. Expert Member
      Akos | | #26

      I've done 6' spacing tied together with 12' 2x6 on flat over the top. The lumber on flat needs to be continuous between the posts that are dug down to support the semi free standing one.

  8. PLIERS | | #27

    Thank you for all the great advice. After thinking this over the easiest way to do this would be to box around the old chain link fence posts with wood, and use the 2x6 across too as Akos recommended because existing posts are 6’ apart. I think on side splitting my neighbor I want to use trees because of the proximity of his fence. The problem is I have the wrong tree now hemlocks need pruning and they are just too wide. Anyone have suggestion on a narrow evergreen privacy tree that will grow fast and survive in westchester county ny climate? Also how many feet from my neighbors fence can I plant it without ever causing disruption to his fence. I don’t want to screw over my neighbor.

  9. artisanfarms | | #28

    Arbor Vitae is narrow, hardy in your zone, evergreen and grows reasonably fast. I'd plant it at least 8-10' from the fence to give you room to prune it as needed.

    1. Expert Member
      DCcontrarian | | #29

      Privet would also work well there.

    2. PLIERS | | #30

      10’ is about half my yard space. I would like to use an arb, do you think I need that much space? There’s some narrow arbs that have a 3 foot width, would that mean about 2 feet minimum from fence would cover it? 1.5 feet growth on each side of trunk

  10. PLIERS | | #31

    So looking over this project my old retaining wall is weak and needs to be replaced. I have a foot of space behind my old retaining wall to build a new one. I want to incorporate a 6 foot vinyl fence on top of the retaining wall or the fence at least very close to the retaining wall. The retaining wall is 2 feet tall. I see this device that you can build the fence right up to retaining wall. Sleeve-It SD1 - Sold as Set of 5, Code Compliant Post Anchoring Solution, Used to Anchor Fence Posts and Hand Rails on top of Segmental Retaining Walls, Easy to Install However it’s an extra cost. Is there an easier way to incorporate the retaining wall and 6ft fence without spacing the fence too far from the retaining wall?

    1. Expert Member
      DCcontrarian | | #32

      I once did a retaining wall almost exactly like this, 24" high with fence posts incorporated. The wall was made out of 4x4 wood. The fence posts were in 36" post holes (measured from the bottom of the wall) and then bolted to dead man anchors going back into the hillside. I can't remember whether I used timber spikes or Timber-Lok screws to hold the horizontal beams to the posts and to each other.

  11. PLIERS | | #33

    So the fence posts were 36 inches from bottom of retaining wall. Was the post inside of the retaining wall or on the outside. Could I use 4x4 wood posts but use retaining block stones for wall with this setup instead of wood?

    1. Expert Member
      DCcontrarian | | #34

      The posts were part of the retaining wall, the whole retaining wall was wood.

  12. PLIERS | | #35

    Would wood work better in this situation? Here’s a dumb question but if I dug down a foot and installed a 36” deep sono tube and embeded a 9 foot 4x4 in concrete and then filled in the rest with soil would that work?

    1. Expert Member
      DCcontrarian | | #36

      What I did wasn't engineered, it just felt better to me that way. Fences can have a lot of lateral force, the wind can blow them over. So the deeper you can go with the fence posts the better. Retaining walls are meant to resist lateral forces, but not so much the overturning forces that a fence gets. The problem you run into usually when you put a fence on a retaining wall is the retaining wall doesn't contribute anything to keeping the fence from overturning, but it means you need to have much longer fence poles so the overturning forces are a lot greater.

      My gut feeling is that if you mixed stone and wood the stone wouldn't really be attached to the wood, and if the post started to move the stone would just move around it. So the 2' above ground doesn't really contribute to stabilizing the post. If you want 6' of fence above the wall then that's 8' of fence above the ground, I'd want at least 40" of post in the ground so that's a 12' post. I'd also want probably at least 4' of deadman going back into the hill. Concrete on the base would help but there's no substitute for depth.

      If you wanted to do stacked stone after the posts were set and in front of the posts I think that would work.

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