Does a higher-Rw board guarantee a quieter wall?

No single board has an Rw — the rating belongs to the tested partition. A denser board helps, but cavity width, insulation, decoupling and workmanship move the result just as much.

Why is the on-site figure lower than the quoted Rw?

Lab Rw suppresses flanking transmission and reflects ideal build quality. On site, sound flanks through junctions and services and workmanship varies, so field values (DnT,w) typically come in a few dB below the lab number.

Ctr is a spectrum adaptation term added to Rw or DnT,w to weight the rating towards lower-frequency sound (such as traffic and music). Regulations for dwellings are commonly written as DnT,w + Ctr.

Rw — airborne sound insulation

What does the Rw number on a partition system mean?

Rw is lab-measured airborne sound insulation in dB — higher numbers block more sound. On-site performance is usually a few dB lower; always verify against manufacturer system data.

Rw is a single number distilled from a board-system’s performance across a range of frequencies (to ISO 717-1). It is convenient shorthand, but it belongs to a tested wall or floor, not to a sheet of plasterboard — and the gap between the lab figure and what a finished room actually achieves is where most acoustic disappointment comes from.

Lab Rw vs on-site performance

Rw is measured in a laboratory with the flanking paths — the ways sound sneaks around a partition through the surrounding structure — deliberately suppressed. A real building has junctions, service penetrations and workmanship variation, so the field result is usually a few decibels lower than the lab Rw.

That is why UK regulation is written in field terms. Approved Document E (England and Wales) sets on-site standards using DnT,w + Ctr for airborne sound between dwellings — as an indication, of the order of 45 dB for separating walls in new build and 43 dB in conversions — measured in the completed building, not read off a board.

Where the board comes in

Airborne sound insulation is driven by mass, separation and absorption. Heavier leaves resist sound better (the mass law), decoupling the two faces of a partition helps, and cavity insulation damps the space between.

The board contributes mass — which is exactly why acoustic boards are dense (EN 520 Type D) and why specifiers reach for a second layer or a heavier board to lift performance. But the Rw is a property of the whole assembly: studs, cavity width, insulation and layering all move the number as much as the board does.

Reading acoustic figures honestly

Because Rw belongs to the tested system, a board’s density or mass per square metre is a useful comparison signal but not an Rw in its own right. When you are matching boards across brands, matching the mass and EN 520 type gets you a like-for-like leaf; the system’s acoustic rating still has to come from the system’s own test data.

drywallDB keeps that line clear: it compares boards on declared mass and classification, and treats system-level acoustic performance as something to verify against the manufacturer’s tested build-up rather than infer from a single sheet.

If an older spec cites BS 2750

BS 2750, the former British Standard for measuring sound insulation, has long been withdrawn. Measurement now follows the international ISO series — BS EN ISO 16283 in the field, ISO 10140 in the lab — and the single-number Rw rating comes from BS EN ISO 717-1. A “dB to BS 2750” figure describes the same physical quantity under a superseded method: treat it as historical, and ask for current test data.

Frequently asked questions

Does a higher-Rw board guarantee a quieter wall?: No single board has an Rw — the rating belongs to the tested partition. A denser board helps, but cavity width, insulation, decoupling and workmanship move the result just as much.
Why is the on-site figure lower than the quoted Rw?: Lab Rw suppresses flanking transmission and reflects ideal build quality. On site, sound flanks through junctions and services and workmanship varies, so field values (DnT,w) typically come in a few dB below the lab number.
What is Ctr?: Ctr is a spectrum adaptation term added to Rw or DnT,w to weight the rating towards lower-frequency sound (such as traffic and music). Regulations for dwellings are commonly written as DnT,w + Ctr.

Related guides

Plasterboard weight: kg/m² and per board — How heavy is a plasterboard, and why do brands declare it differently?
EN 520 board types explained — What do EN 520 Type A, D, E, F, H, I, P and R mean?
Reaction to fire vs fire resistance — Are 'A2-s1, d0' and '60 minutes' the same kind of fire rating?

This copy powers drywallDB’s in-app tooltips. The product behind it searches every UK plasterboard, compares cross-brand equivalents and cites every value to its manufacturer data sheet. Start free — 7 days, no card.