A wind fence is set by porosity and height, not by how solid it looks

By Johnny · 23 October 2026 · 6 min read

The fence is the cheapest structure on a bulk site and the one most often built wrong. The mistake is almost always the same: it is built to look solid.

A solid wall reads as protection. In aerodynamic terms it is the opposite. Air arriving at a solid wall has nowhere to go but up and over, and it comes back down behind the wall as a strong recirculating vortex that scours the pile harder than open wind would have. Yards with a solid wall report more dust at the stockpile than yards with no wall at all, and the reason is not the wall's height or its quality of construction — it is that the wall has no porosity.

What the fence is actually doing

A permeable fence works by bleeding air through itself and creating a sheltered wake behind. The wake is a region of reduced velocity, and its size and strength are set by two numbers: how much open area the fence has, and how tall it is relative to what it is protecting.

Those two numbers, not the material or the finish, decide whether the fence does anything.

Porosity: the working range is narrow

Open area in the region of forty to fifty per cent is the range that reduces wind speed behind the fence without generating a damaging recirculation. Below that the fence starts behaving like a wall and the vortex returns. Above it, too much air passes through and the wake is too weak to matter.

The practical consequence is that a fence built from closely spaced boards, or from solid panels with a few slots, is in the wrong range even if it looks engineered. Louvred panels and mesh with the right open area are not decorative choices — they are the working parts of the device.

It also means porosity is worth verifying after construction, not just specifying. Panels get infilled with debris, guards get added, signage gets bolted on, and a fence that was 45 per cent open at handover can be 25 per cent open a year later.

Height sets the length of the protected zone

The sheltered wake extends downwind roughly ten to fifteen times the fence height, with the strongest reduction close behind the fence and the effect fading with distance.

That single relationship decides most fence layouts. A four-metre fence shelters a zone on the order of forty to sixty metres. A pile longer than that is not protected at its far end, and no amount of extra posts changes it — the answer is a taller fence, or a second fence line, or accepting that the far end is exposed.

This is where most yards get their numbers wrong: the fence is sized to the boundary, not to the pile. A fence that runs the length of the site at four metres protects the first part of the pile well and the rest hardly at all.

Distance from the pile matters as much as the fence

A fence placed tight against the stockpile puts the wake in the wrong place. The sheltered zone forms a few fence heights downwind, so a fence standing one metre from the pile has its wake forming inside the pile rather than over it.

Set back far enough that the wake develops over the material and the same fence does noticeably more work. That setback is a site-planning decision made at layout stage, and it is very hard to recover later because the space in front of a stockpile is exactly the space the loader wants.

One side is rarely enough

Wind does not arrive from one direction all year, and a fence on the prevailing side leaves the pile exposed for the rest of it.

For a yard where dust is a regulatory issue rather than a nuisance, the honest configuration is fencing on two or three sides, accepting that the corners — where two wakes meet — are the least protected part of the yard and the place where dust will still leave.

The corner is also where the structure is loaded most: a fence corner takes wind from two directions and the posts at that corner carry the sum. Detailing them like the straight run is a common and avoidable failure.

The foundation and the puddle

A fence line is usually the low point of a yard, because yards are graded to drain outward and the fence is at the edge.

That puts every post in the place water collects. Posts set in a puddle corrode from the ground line up, which is the part nobody inspects and the part that fails first. Setting yard levels so water runs to a collection line away from the fence, and detailing the post base so it is not permanently wet, costs almost nothing at construction and is impossible to retrofit.

What I want before drawings

• The pile dimensions, the material, and what fraction of it is fines.
• The prevailing wind directions across the year, and what lies downwind of the yard.
• Whether the driver of the fence is dust leaving the site, or material being lost from the pile — they lead to different layouts.
• How the yard is worked: dozers pushing from a fixed face, or a loader moving around the pile. The working pattern decides where the fence cannot stand.
• The space available between the fence line and the pile.
• The wind speed to be used, taken from the applicable code at the project site rather than a round number, plus the fence's own edge detail — a permeable fence is a light structure with a large sail area, and the corner posts and end returns carry loads the straight run does not.

A fence is a wind device, and like any device it has a working range. Specify the open area, size the height to the pile, stand it back far enough for the wake to form, and it will do what it was bought for. Build it solid, and it will make things worse while looking like the most serious thing on site.