Temporary Fence Scrim, Signage and Wind Loading in New Zealand

Scrim, shade cloth, printed banner mesh, signage, sound mats, acoustic blankets, dust mesh and plastic sheeting can all increase the wind load on temporary fencing.

The practical rule is simple:

If it blocks wind, it changes the fence design assumption.

A temporary fence run that is stable as open mesh may become unstable once screening, signage or acoustic material is attached. The more solid the attachment, the more the fence behaves like a sail.

In New Zealand, there is no single temporary fencing rule that covers every site condition. Fence stability is normally managed through site-specific risk assessment, manufacturer requirements, WorkSafe expectations, council conditions, the Building Code where relevant, and the PCBU’s duties under the Health and Safety at Work Act 2015.

For low-risk, sheltered sites, light permeable scrim may only require extra checks and moderate bracing. For 70–90% blockout scrim, printed banner mesh, repeated signage, sound mats or acoustic blankets, the fence should be treated as a high wind-load installation.

On exposed, public-facing, long-duration or heavily screened sites, get manufacturer guidance or a suitably qualified engineering review before installation.

Practical bracing guide

This table is a practical Tower Temporary Fencing guide only. It is not site-specific engineering design, temporary works design, certification, or a substitute for manufacturer requirements.

Actual bracing may need to increase depending on wind exposure, terrain, ground condition, fence height, fence condition, installation quality, public interface, traffic exposure, duration, scrim type, signage area, acoustic mat weight and project-specific risk assessment.

Blockout is not the same as permeability

Scrim and shade cloth are often described using percentages such as 30%, 70% or 90%. These percentages are not always used consistently between suppliers.

For this guide:

These percentages are indicative only. Real wind performance depends on weave type, fibre density, printed ink coverage, overlap, age, tension, dirt build-up, moisture, edge fixing, tie spacing and whether multiple layers are installed.

A 70% shade cloth, 70% printed banner mesh and 70% privacy screen may not behave the same way in wind. Printed products can be less permeable than expected because ink coverage and laminated finishes can close the weave.

Why fence-mounted products increase wind load

Open mesh fencing lets much of the wind pass through. Once scrim, shade cloth, banners, signage, sound mats or plastic sheeting are attached, the projected wind area increases.

Wind pressure rises quickly as wind speed increases. A fence can appear stable in ordinary wind and still fail in gusts.

A simplified dynamic pressure relationship is:

q = 0.5 × ρ × V²

Where:

• q = wind pressure in Pascals
• ρ = air density, commonly taken as about 1.2 kg/m³
• V = wind speed in metres per second

The practical point is that wind pressure increases with the square of wind speed. If wind speed doubles, wind pressure increases by about four times.

Formal wind assessment is more involved than this simple formula. AS/NZS 1170.2:2021 provides the wind-action framework used in New Zealand structural design. A proper assessment considers wind region, terrain, shielding, topography, direction, height, design life, importance level, projected area, drag behaviour and the actual fence restraint system.

Product-specific guidance

Open temporary mesh fence

Open mesh fencing has the lowest wind-load profile because air passes through the panel. That does not mean it needs no bracing.

Brace ends, corners, gates, long runs, sloped ground, exposed areas and public-facing interfaces. Treat open mesh as the baseline condition. Every fence-mounted product should be assessed as a modification to that baseline.

30% blockout scrim / light dust mesh

A 30% blockout product is usually relatively open. It can improve site presentation and reduce visible dust movement while still allowing much of the wind to pass through.

It is the lowest-risk screening category, but it is not risk-free. On coastal, hilltop, open subdivision, road corridor or public-facing sites, even light scrim may justify extra bracing and more frequent inspection.

Practical guide: brace every 3rd panel.

50% blockout scrim / medium shade cloth

A 50% blockout product creates a meaningful change in wind behaviour. It gives better screening than light mesh, but it also increases overturning load.

Do not add medium scrim to a standard fence and “see how it goes.” Install bracing before the fence is exposed to strong wind.

Practical guide: brace every 2nd panel.

70% blockout scrim / heavy shade cloth

A 70% blockout product is a high wind-load attachment. It may be useful for privacy, dust reduction, visual screening or public-facing presentation, but it can substantially increase overturning risk.

On exposed or public-facing sites, 70% blockout should trigger a documented bracing review. Standard feet and clamps alone should not be assumed sufficient.

Practical guide: brace every 2nd panel and increase ballast or use 3 feet per braced bay where practicable.

90% blockout scrim / privacy mesh

A 90% blockout product behaves close to a solid screen from a wind-risk perspective. It should not be treated as normal temporary fence scrim.

For exposed wind, road frontage, public footpaths, schools, long-duration installations or high-risk interfaces, obtain manufacturer-specific bracing guidance or an engineering review.

Practical guide: brace every 2nd panel with 3 feet per braced bay where practicable.

Printed banner mesh

Printed banner mesh is often more wind-sensitive than expected. Ink coverage, laminated finishes and dense weave can reduce permeability.

Do not assume that “mesh” means low wind load. A continuous printed banner across multiple panels should be treated similarly to high-blockout scrim unless product data shows otherwise.

Practical guide: brace every 2nd panel, or every banner bay where the banner is large or repeated.

Individual safety signs

Small individual safety signs usually have limited wind impact if isolated and properly fixed.

Risk increases when signs are large, closely spaced, mounted high, double-sided, fixed to exposed fence runs or grouped into continuous notice boards.

Do not remove essential safety signs to reduce wind load. Fix them properly, avoid oversized boards on exposed fence lines and brace the fence where signage creates a meaningful wind face.

Large corflute signs, site notice boards and advertising boards

Large rigid signs can be more problematic than fabric scrim because they create concentrated load points. Practical guide: brace every panel carrying a large sign, or use independent support.

Sound mats and acoustic blankets

Sound mats are high-risk from a wind-load perspective. They are usually dense, heavy and low-permeability. Some can also hold moisture, increasing dead load on panels and couplers. Practical guide: brace every 2nd panel with 3 feet per braced bay where practicable. Use independent support or engineering review for exposed public-facing sites.

Tarpaulins, plastic sheeting and impermeable wraps

Impermeable products create the highest wind risk. They can quickly turn a fence into a sail. They should generally be avoided on standard temporary fencing.

Practical bracing options

Standard temporary fence braces

Purpose-made temporary fence braces are usually the cleanest option where space allows. They are designed for the fence system and are easier to install consistently.

Use them for screened runs, gates, corners, exposed boundaries, long fence lines and public interfaces.

1.8 m Y-posts

Y-posts can be useful where standard angled braces do not fit and the ground allows driven posts. They provide a closer support line to the fence than conventional angled braces.

Check underground services before driving posts. Pull-out resistance depends on soil condition and embedment.

Bracing timbers

Timber bracing can work on constrained civil sites or irregular ground, but it is more dependent on competent installation.

Timber quality, fixings, bearing points and trip hazards matter. Treat timber bracing as a temporary works method, not an improvised prop.

Fence returns

Returns are one of the simplest ways to improve stability. A long straight fence line is weak in overturning. Returns create plan stiffness.

Use returns at ends, corners, gate areas and screened runs where space allows.

Concrete blocks and deadman blocks

Concrete blocks can help resist sliding and overturning, especially on hardstand where posts cannot be driven.

Blocks must be positively located and must not create public hazards. Loose blocks placed randomly on feet are not a robust bracing method.

Independent posts or frames

Where wind loading is high and fence-mounted controls are essential, stop relying on the temporary fence panel as the main support.

Use independent posts, frames, scaffold-supported systems, hoarding or purpose-designed acoustic barriers for large signs, continuous banners, sound mats and near-solid screening.

Field checklist

Before installing scrim, signage or acoustic products on temporary fencing:

• Use the most permeable product that still achieves the site purpose.
• Keep screening discontinuous where possible.
• Brace before installing screening.
• Brace gates, ends and corners first.
• Use returns where space allows.
• Use Y-posts only where ground conditions and service locations allow.
• Use concrete or deadman blocks on hardstand where suitable.
• Use independent supports for large signs, continuous banners and acoustic mats.
• Inspect after installation, strong wind, impact, vandalism or ground movement.
• Remove, roll up or reduce screening before severe wind if the system is not designed for it.