Setting a fence post up to 3.8 m

In price lists, "post height" usually means the total length of the post, not the height of the fence above ground. Part of the post sits in the concrete footing, usually roughly 80 to 100 cm. A 3.8 m post therefore leaves around 2.8 to 3 metres above ground. Before you order, agree with the contractor how they measure it, because a difference of one metre changes the whole project.

Typical situations where this variant makes sense:

• Mesh fencing around a sports pitch, tennis court or school playground, where balls must not fly over
• Ball-stop netting behind a goal or next to a road, protecting the surroundings
• A tall fence along a busy road or a neighbour's boundary, where the owner wants privacy and adds a screening fabric to the mesh
• Fences with two rows of mesh stacked on top of each other, or with a barbed wire extension, around yards and storage sites
• Posts that carry a gate, a pedestrian gate or a gate motor, and therefore need to be longer and anchored deeper than the posts around them

If your fence is no more than about two metres above ground, a tall post only adds work and material to the footing. In that case, choose a shorter variant.

At first sight all three items are the same job: the post goes into a hole and is concreted in. The difference lies in the forces the post has to take, and those grow faster with height than most people expect. Wind acts on the whole surface of the fence, and the taller the post stands above ground, the bigger the lever it puts on the footing.

• Post up to 2.4 m: a standard garden fence with mesh or panels, roughly 1.5 to 2 m high. The footing is smaller, and one experienced person with a helper can set the post from the ground without a ladder.
• Post up to 2.7 m: a fence of around two metres with some extra length, for example with an extension, or on a slope where heights have to be evened out. The footing has to work harder, but the method stays the same.
• Post up to 3.8 m: a fence about three metres high. The footing has to be deeper and wider, the post stronger, the struts more frequent and the posts closer together. Setting it takes at least two people, a ladder to check the top, and temporary bracing until the concrete has hardened.

In practice, a 3.8 m post is not just a slightly longer post. It is heavier and harder to handle. Any deviation from vertical shows up much more at the top, and a weak footing makes a whole section of fence lean. Each post therefore takes longer and needs more concrete.

Choosing the post

On a tall fence, the stiffness of the profile decides everything. A thin round post that is fine on a two-metre fence will start to bend at three metres once screening fabric catches the wind.

• Round steel posts, galvanised and often PVC-coated, are the most common choice for mesh fencing. For a tall fence a larger diameter and thicker wall are used, usually following the fence system manufacturer's recommendation.
• Box sections, meaning rectangular or square hollow steel profiles, are stiffer in one direction. A rectangular post is turned so that its longer side runs at right angles to the fence line, where it resists the wind better.
• Posts for panel systems are less common at this height, because panels are usually lower. If panels are stacked on top of each other, follow the manufacturer's instructions.
• Timber posts of this length are heavy and rot in the ground. If you want timber, it should stand on a steel post support above ground, not in concrete.
• Concrete posts are very heavy, and with three metres above ground they are hard to set without machinery.

Concrete footing in the ground

The most common method is a separate concrete footing for each post. For a tall post the hole is usually dug roughly 80 to 100 cm deep, so the footing sits below local frost depth, and generally at least 30 cm wide. Corner and gate posts need more. A few centimetres of gravel go at the bottom so that water can drain away. The concrete is usually around strength class C16/20 to C20/25, either mixed on site or delivered by a ready-mix truck when there are many posts. Bagged dry concrete mix is convenient, but deep footings need a lot of it, and it must be mixed and compacted properly.

Posts in a dwarf wall

If the fence stands on a low wall of hollow formwork blocks, the post is concreted into the block cores or into the foundation underneath. For a tall post it is not enough to set it only into the blocks. It should reach down into the strip foundation. Otherwise the wind pushes against the top course of blocks and can split them apart.

Base plates and ground screws

A post with a welded base plate can be bolted onto existing concrete, such as a wall. At around 3.8 m, though, the anchors take large forces, and this solution should be checked by a structural engineer or at least by the fence system manufacturer. Ground screws are quick and need no concrete. On tall fences with fabric, how much they can hold depends on the soil, and the manufacturer has to confirm it.

Most problems with tall posts start before any concrete is poured. Check these points before work begins:

• The boundary. For a fence on the boundary line, it pays to have a surveyor mark the boundary points. Moving a three-metre post that is already concreted in is far more work than moving a low one.
• Underground services. Ask the utility companies, or a cable and pipe locating service, to mark electricity, gas, water, drainage and telecoms lines. A hole almost a metre deep can easily hit a cable or a pipe.
• Permission. A fence around three metres high is not a minor matter for planning purposes. In many places, fences above a certain height, or next to a road, need permission. Check with your local building or planning authority before you start, and do not assume it will be fine. Next to a road, the highway authority may also have a say. For a block of flats, the building management or owners' association decides on fencing.
• Access. The posts are long, so they have to be delivered and laid out along the fence line. If the holes are drilled with a powered auger or dug with a mini excavator, the machine has to reach the fence line.
• Cables and ducts. If you plan a gate motor, lighting or a doorbell, the cable ducts must be in the ground before the concrete goes in. The wiring itself is a job for a qualified electrician.
• The old fence. Pulling out old posts with concrete footings is a separate job. Agree beforehand who does it and where the rubble goes.

On site, the work usually goes like this. First a string line is stretched along the fence line and the post positions are marked. On a tall fence the posts are closer together than on a low one, often around 2 to 2.5 metres apart, depending on the system and whether the fence will carry fabric. Corner, end and gate posts go in first, because all the others are lined up against them.

The holes are dug by hand, with a powered auger or with machinery. A layer of gravel goes at the bottom. The post is stood in the hole and packed up to the right height. With a three-metre post, the height is checked against a string line stretched between the tops of the corner posts, or with a laser level, not just measured from the ground, because the ground is rarely level.

Next comes the most important moment: getting the post vertical. It is checked with a spirit level in two directions, along the fence and across it. At this length a long spirit level or a plumb line is recommended, because a short level misses a lean that shows up as several centimetres at the top. The post is then braced with two or three battens pushed into the ground, so it cannot move while the concrete is poured and while it sets.

The concrete goes in in layers and each layer is compacted with a rod or a tamper, so no voids are left in the footing. The vertical is checked again during pouring, because wet concrete can easily push the post out of line. The top of the footing is shaped into a slight cone sloping away from the post, so water runs off instead of standing against the steel.

Struts are part of the job on a tall fence. They go at corners, end posts, gate posts and changes of direction, and on long runs also at intervals, for example roughly every 25 metres depending on the system. Each strut has its own small footing and is fixed to the post with a clamp or a bolt. On a three-metre fence it is usually a good idea to strut a corner post from both sides.

The same post can take half the time on one plot that it takes on another. Level ground, soft loamy soil without stones, good access for the auger and a clearly marked boundary all make the work easier. It also helps when the posts are ready on site and the concrete can be mixed right next to the fence line.

Things that make it harder:

• Stony or rocky ground, where an auger is not enough and the hole has to be broken out or dug with heavier equipment
• Heavy clay, which sticks to tools and holds water in the hole after rain
• A high water table, where the hole floods and the concrete has to be placed more carefully
• A slope, where post heights have to step down and the struts come in different lengths
• Tree roots, old foundations or remains of the previous fence
• Services in the fence line, where digging has to be done slowly and by hand
• Narrow access, where long posts have to be carried by hand over a long distance

Weather matters more with tall posts too. In strong wind, a three-metre post is hard to hold vertical, and fresh concrete can shift underneath it. Concrete should not be poured in frost unless the manufacturer says otherwise.

You can set a post up to 3.8 m yourself if you have the skills and at least one helper. You cannot do it alone: the post is long and heavy, and if it falls it can injure someone. Have the underground services marked before you dig. If you hit a gas pipe and smell gas, leave the area immediately, do not use naked flames or switch on electrical devices, and call the gas emergency line or 112. If you uncover a cable, stop work and contact the network operator.

1. Check the boundary, the marked services and what your local building authority requires.
2. Stretch a string line along the fence and mark the corner and intermediate post positions.
3. Dig the holes roughly 80 to 100 cm deep and at least 30 cm wide, wider for corner and gate posts.
4. Put a layer of gravel at the bottom of each hole and tamp it down.
5. Fit a cap on top of the post so rainwater cannot get in.
6. Stand the post in the hole with your helper, set the height to the string line and pack it up.
7. Check the vertical in two directions with a long spirit level and brace the post with battens.
8. Mix the concrete as the manufacturer instructs and place it in layers, compacting each one.
9. Check the vertical and the height again and again while pouring.
10. Shape the top of the footing into a cone sloping away from the post.
11. Leave the concrete to cure, keep it damp for the first few days in warm weather and leave the bracing in place.
12. Fit the struts and tension the mesh only once the concrete has hardened enough.

When you check the top of the post from a ladder, make sure the ladder is stable and someone holds it. If the fence carries a gate motor or lighting, leave all electrical work to an electrician.

Mistakes on tall posts do not go unnoticed. What gets away with it on a low fence shows up here by the first winter or the first storm.

• Shallow footing. Over time the post leans in the direction of the prevailing wind, and frost can lift it. On a three-metre fence the lean is visible from the street.
• Narrow hole. If the hole is only slightly wider than the post, the concrete forms a thin sleeve and the post flexes inside it like a pipe in a tube.
• Concrete below ground level with no slope. A dip forms around the post and water collects in it. The steel at the base starts to corrode sooner and frost can break up the concrete.
• Open post top. Water runs into the tube, freezes in winter and can split the post. A cap is a small thing, but it matters.
• Missing or weak struts. Once the mesh is tensioned, the corner posts bend inwards and the mesh goes slack.
• Tensioning the mesh too early. Fresh concrete cannot hold the pull of the line wires and the post moves. Mesh is usually tensioned after several days at the earliest, later in cold weather.
• Fabric that was never planned for. The owner later hangs a shade or privacy screen on a fence that was not designed for it. The fence suddenly behaves like a sail and the posts lean over.
• Damaged galvanising. Cutting a post to length exposes bare steel. Without touching it up with zinc spray, the cut starts to rust.

The time per post depends mainly on the soil and the access. In soft ground with an auger, far more posts go in per day than on a stony slope dug by hand. Corner and gate posts take longer because they have bigger footings and struts, and lining them up is more demanding.

Concrete needs time. For the first few days the post should carry no load and the bracing should stay in place. Mesh, line wires and fabric are usually fitted after roughly a week, later in cold weather. Concrete generally reaches its full strength after about 28 days. A heavy gate or a gate motor is best hung once the concrete has hardened well, following the gate supplier's advice.

After the posts come the mesh or netting, and possibly the gate and its motor. Agree the order in advance, so the mesh installer does not turn up before the concrete has hardened, and so the electrician is involved when the ducts are laid.

Check the posts before the mesh goes on, while everything is easy to see and any correction is still simple. Look along the row of posts from one end of the fence: the tops should form a smooth line and the posts should stand in one straight line. Check a few posts at random for vertical with a long spirit level. At handover, go through this list:

• The posts stand in the agreed positions and in line with the string
• The post tops are at an even height or follow the slope smoothly
• The posts are vertical in both directions, including corner and gate posts
• The spacing matches what was agreed and what the fence system requires
• The footings have the agreed depth and width, ideally backed up by photos taken during pouring
• The concrete surface slopes away from the post and no water stands against it
• Struts are fitted at corners, ends, gates and changes of direction
• All posts have caps and any cut ends have had their coating repaired
• Cable ducts are laid where they were planned
• The posts do not move when you push the top by hand
• The site is tidy and the excavated soil has been removed or spread as agreed