What is an Rw 26 dB acoustic barrier and is it enough?

There's a grey or green wall of padded panels clipped to the site fence next door, and the breaker behind it still sounds far too loud. You've been told it's an "acoustic barrier rated at 26 dB". So why doesn't it feel 26 dB quieter?

If you're trying to work from home, get a baby down for a nap or just enjoy your garden, that gap between the label and what you hear is frustrating. It can feel as though nobody is being straight with you.

This article explains what an Rw 26 dB barrier actually is, what it can and can't do on a real site, and how to tell whether the one next to you is doing its job.

In this article you'll learn:

• What "Rw 26 dB" and "αw" mean in plain English
• Why the reduction you hear is always lower than the lab rating
• How to judge whether a barrier is installed properly
• When Rw 26 dB is enough, and when the site needs something heavier
• What to ask the contractor or the council for

What is an acoustic barrier rating?

Rw (weighted sound reduction index) is a single number, in decibels, that says how well a material stops sound passing straight through it, measured in a laboratory to ISO 10140 and calculated to ISO 717-1. The higher the number, the less sound gets through the material itself.

So an Rw 26 dB panel, tested in a lab between two sealed rooms, earns a single-number rating of 26 dB for sound passing through the material. That's a large reduction on paper. The catch is the words "in a lab".

αw (weighted sound absorption coefficient) is a number between 0 and 1, rated to ISO 11654, that says how much sound a surface soaks up rather than reflects. An αw of 0.9 means roughly 90% of the sound hitting the face is absorbed. That matters on a construction site, because a hard barrier can bounce noise back across the works and out over the top.

dB(A) is a sound level weighted to match how the human ear hears, and it's the unit councils normally use when they measure noise at your home.

Why is the reduction on site lower than the Rw rating?

Short answer: sound doesn't only travel through a barrier. It also goes over it and around it.

In the lab, the panel is the only path. On site, noise bends (diffracts) over the top edge and around the ends, and leaks through any gap at the joints or along the ground. The reduction you actually get at your window is called the insertion loss: the difference in noise level at a given point with the barrier in place compared with no barrier at all.

Insertion loss depends on:

• Height. If you can see the machine from your window, the barrier isn't blocking the direct path.
• Distance from the source. A barrier close to the noisy plant works far better than one on a boundary 30 metres away.
• Gaps. A small gap at a joint or under the base can undo much of the panel's performance.
• Frequency. Low, rumbling noise (large engines, piling) bends round obstacles more easily than higher-pitched noise.

A real example helps. Hushtec reports a pile shroud using its Rw 32 dB Premium material reducing a piling rig from 89.9 dB to 82.7 dB at Woodhall Golf & Spa. That's a useful 7.2 dB, but well short of 32 dB, because the measured result includes every path the sound took. Expect the same pattern with any barrier, from any supplier.

Is Rw 26 dB enough?

It depends — mainly on three things: what's making the noise, how close you are, and how well the barrier is installed.

For most temporary barriers, the panel itself is rarely the weak point. Once the material is reasonably good, sound going over the top and around the ends usually limits what you hear. That's why a well-installed Rw 26 dB barrier can outperform a poorly installed heavier one.

Rw 26 dB is generally a sensible choice for:

• General site perimeter screening on fences
• Small plant: compressors, generators, cutting stations, mixers
• Short-duration works near homes
• Sites where panels are moved and refitted often, so lighter weight helps

It's often not enough on its own for:

• Piling, rock breaking and heavy demolition right next to homes
• Long-running works with a lot of low-frequency noise
• Situations where your window is above the top of the barrier

In those cases the better answer is usually a heavier barrier, a shroud or enclosure around the machine itself, or a taller supported wall. BS 5228-1:2009+A1:2014 is the UK code of practice for noise control on construction and open sites, and it's the document councils and contractors usually refer to when judging whether noise is being properly controlled.

What makes a good acoustic barrier?

Use this checklist when you look over the fence. You don't need a sound meter for most of it.

• Height: it should break the line of sight between the noisy machine and your windows, including upstairs.
• No gaps at joints: panels should overlap or be sealed edge to edge.
• No gap at the base: the bottom should sit on or close to the ground, not hang 20 cm above it.
• Close to the source: the nearer the barrier is to the plant, the better it works.
• Absorptive face towards the works: the soft, padded side should face the machinery.
• A stated Rw rating: ideally with the test standard (ISO 10140 / ISO 717-1).
• A stated absorption figure: αw to ISO 11654, or an equivalent.
• Secure fixing: panels flapping in the wind leave gaps and can be a safety risk.

Hushtec Performance barrier: what it is and how it compares

This site is supported by Hushtec, a UK manufacturer of temporary acoustic barriers made in Wakefield, West Yorkshire.

The Hushtec Performance barrier is the company's entry-level temporary acoustic panel. It is designed to be clipped to site fencing, scaffolding or frames to form a continuous wall or enclosure.

From Hushtec's product page and reference data:

• Sound insulation: Rw 26 dB. The product page also lists STC 26, the American rating that does a similar job.
• Absorption: quoted as NRC 0.9, an American absorption rating similar in purpose to αw. If your project requires αw to ISO 11654, ask for that figure specifically.
• Construction: PVC outer with an acoustic foam core; no fibreglass.
• Panel size: 2000 mm × 1250 mm as standard, with custom sizes on request.
• Fixing: stainless steel eyelets and hook-and-loop (Velcro) edges on all four sides, so panels join to form walls of any length.
• Weather: described as waterproof and snowproof, rated –40 °C to +70 °C.
• Fire: described as "fire-rated". No classification is given on the product page, so ask for the test certificate if this matters on your site.

One caution. Like many manufacturers' pages, Hushtec's headline "up to" noise reduction figure is not the reduction you should expect at your home. Use the Rw rating and the installation checklist above instead.

How does it compare with the rest of the range?

There's a less obvious option too. Two layers of Performance barrier with an air gap between them can outperform a single Premium layer, because the gap decouples the layers so sound has to cross two separate barriers. That's worth asking about where space allows.

Pros

• Light, so it's easier to fit high on fences and move around a changing site
• Highly absorptive face, which helps reduce reflected noise
• Panels join on all four edges, which makes gap-free walls easier to achieve

Cons

• Rw 26 dB is the lowest rating in the range, so it's not the right choice on its own for heavy, sustained works beside homes
• Fence-mounted barriers are limited in height. Where screening needs to be taller than about 2 metres, a supported system such as Hushtec Rapidwall (wind-load tested up to 8 m) is the better route
• Like any barrier, it does little if your window looks over the top of it

What should you ask the contractor or council for?

If a barrier is up but the noise is still a problem, these are fair, specific questions:

• What is the barrier's Rw rating, and to which standard was it tested?
• Was the barrier chosen as part of a noise assessment under BS 5228-1:2009+A1:2014?
• Has the council agreed noise limits or working hours for the works, and what are they?
• Can the barrier be raised, moved closer to the plant, or sealed at the base?
• Can the loudest machines be shrouded or enclosed instead?

Before you complain: checklist

• Can you see the machine over or around the barrier from your window?
• Are there visible gaps at the joints or under the base?
• Is the padded face pointing towards the works?
• Is the barrier close to the noise, or far away on the boundary?
• Have you asked the contractor for the barrier's Rw rating and the site's noise limits?
• Have you kept a dated record of when the noise is worst?

If the answers point to a poor installation, raise it with the site manager first. If nothing changes, contact your council's Environmental Health team.

For next steps, see our guides on machine noise, what contractors should be doing and how to make a complaint. You can estimate noise at your property with the noise calculator, or browse more in the Learning Centre and FAQ.

This article is general guidance, not legal or engineering advice. For your specific situation, contact your council's Environmental Health team or a qualified acoustic consultant.