Sound reduction index (SRI)
The sound reduction index (SRI, or sometimes just R) is a measure of the reduction in the intensity of sound when it passes through part of a building; in other words, the level of sound insulation provided. It is the difference between the sound intensity that hits one side of an object (such as a wall, door, window, partition and so on) and the sound intensity measured on the other side, expressed in decibels (dB).
When sound hits the surface of a material, some will be reflected, some will be absorbed by the material and some will be transmitted through it. By determining the SRI, the effectiveness of the element as an insulator (the amount of sound that it has prevented from passing from one side to another) can be assessed.
SRI is defined in the series of international standards ISO 16283 (parts 1-3). Standard testing methods, both in laboratory and field environments, have been established for measuring SRI.
In the USA, the sound transmission class rating is typically measured as the Noise Reduction Coeffiecient (NRC). This measurement is in the process of transitioning to the Sound Absorption Average (SAA).
NB Approved document E: Resistance to the passage of sound, 2003 edition incorporating 2004, 2010, 2013 and 2015 amendments, defines sound reduction index (R) as: ‘A quantity, measured in a laboratory, which characterises the sound insulating properties of a material or building element in a stated frequency band. See BS EN ISO 140-3:1995.’
[edit] Related articles on Designing Buildings
Featured articles and news
Shading for housing, a design guide
A look back at embedding a new culture of shading.
The Architectural Technology Awards
The AT Awards 2025 are open for entries!
ECA Blueprint for Electrification
The 'mosaic of interconnected challenges' and how to deliver the UK’s Transition to Clean Power.
Grenfell Tower Principal Contractor Award notice
Tower repair and maintenance contractor announced as demolition contractor.
Passivhaus social homes benefit from heat pump service
Sixteen new homes designed and built to achieve Passivhaus constructed in Dumfries & Galloway.
CABE Publishes Results of 2025 Building Control Survey
Concern over lack of understanding of how roles have changed since the introduction of the BSA 2022.
British Architectural Sculpture 1851-1951
A rich heritage of decorative and figurative sculpture. Book review.
A programme to tackle the lack of diversity.
Independent Building Control review panel
Five members of the newly established, Grenfell Tower Inquiry recommended, panel appointed.
Welsh Recharging Electrical Skills Charter progresses
ECA progressing on the ‘asks’ of the Recharging Electrical Skills Charter at the Senedd in Wales.
A brief history from 1890s to 2020s.
CIOB and CORBON combine forces
To elevate professional standards in Nigeria’s construction industry.
Amendment to the GB Energy Bill welcomed by ECA
Move prevents nationally-owned energy company from investing in solar panels produced by modern slavery.
Gregor Harvie argues that AI is state-sanctioned theft of IP.
Experimental AI housing target help for councils
Experimental AI could help councils meet housing targets by digitising records.
BSRIA Occupant Wellbeing survey BOW
Occupant satisfaction and wellbeing tool inc. physical environment, indoor facilities, functionality and accessibility.