- Project plans
- Project activities
- Legislation and standards
- Industry context
Last edited 28 Aug 2016
To help develop this article, click ‘Edit this article’ above.
Flanking sound (or flanking noise) is sound that transmits between spaces indirectly, going over or around, rather than directly through the main separating element. This can allow sound to transmit between spaces even though the main separating element itself provides good acoustic insulation.
Approved document E: Resistance to the passage of sound, defines ‘flanking transmission’ as, ‘Sound transmitted between rooms via flanking elements instead of directly through separating elements or along any path other than the direct path’. It defines a ‘flanking element’ as, ‘Any building element that contributes to sound transmission between rooms in a building that is not a separating floor or separating wall’.
A common example of flanking is sound transmitted between two spaces through a floor void (or even a floating screed) that runs under the separating partition, even though the partition provides good acoustic insulation preventing the direct transmission of sound.
- Windows and doors.
- Flanking ceilings, floors and walls which continue past the separating element into the adjoining space.
- Voids such as wall cavities, suspended ceilings and raised floors.
- Penetrating joists.
- Corridors and other circulation spaces.
- Ductwork and pipework.
- Poor workmanship.
Flanking should be considered early in the design stage of new developments and detailing should eliminate or minimise the inadvertent downgrading of sound insulation. Junctions between elements in particular can offer a potential flanking route if they are not carefully detailed and constructed. Good briefing, supervision and inspection on site can help to ensure that the quality of workmanship remains high so that details are constructed as designed.
Flanking can be a particular issue where adjoining spaces have different uses, such as; a lecture theatre next to an office, a private room adjacent to a circulation space, or between neighbouring houses with different patterns of occupancy and behaviour.
Approved document E of the building regulations: Resistance to the passage of sound, sets out requirements for sound insulation between spaces and provides guidance on how to detail separating elements to avoid flanking.
 Find out more
 Related articles on Designing Buildings Wiki
Featured articles and news
How can these valued spaces be reused?
Partnership avoids the need for listed building consent.
Connecting building design from inception to completion to operations.
Gregor Harvie predicts interoperability will be construction’s Uber moment.
Expert commentary and insight.
Guidance offered for stained glass window maintenance.
Define need before determining viability.
Framework examines social value of projects.
RfX or Request for [fill in the blank].
Organisation establishes Equality, Diversity, Inclusion taskforce.
Government announces plans for new building projects.
Outsourcing method to procure and manage supplies.
Joint support of Local Authority Historic Environment and Conservation Services.
The Chesapeake Bay Bridge-Tunnel is an outstanding achievement.
Buildings of the interwar years. Book review.