What is Flanking Sound?

For those of us that do not know what flanking noise is, it is both airborne and impact noise that usually transmits through the fabric of a building. This is mostly a problem through walls that penetrate floors or walls that timber suspended flooring are usually fixed to.

For those wanting to convert an existing dwelling into flats and also for new build, problems like this have to be avoided. Particularly as most flats constructed today have to be tested to prove compliance with the Part E building regulations for noise control through the separating floors. A floor that can be soundproofed to the highest standard can still fail a pre-completion sound test because noise was flanking down the walls!

We will deal with flat conversions first. For most properties built before the advent of cavity walls, flanking noise should not be a problem due to the solid construction of the main supporting walls (usually external) so a separating floor can be upgraded and as long as the work has been conducted correctly, the new flats will pass any required pre-completion sound testing comfortably. However, if a new wall has been built supporting a separating floor in an old building, any subsequent testing could result in a fail because flanking noise down the new wall will have affected the result. Flats built later using the cavity wall system all have lightweight internal walls so it is unlikely these would pass any pre-completion testing unless measures are taken to address the potential flanking noise problem these can create.

This now brings us on to new build constructions. Part E of the Building Regulations recognise that flanking noise is a problem particularly with newly built flats which is why it states that all internal walls, due to their lightweight nature should be sound insulated to stop flanking noise. So newly built walls in old buildings should be similarly insulated to avoid problems with test failures. Even using high density concrete blocks can still result in a test fail if they are not additionally soundproofed so clearly there is a problem here that needs to be addressed.

Sound Service has the answer with their 20mm M20AD sound insulation for walls and is a thin solution. Originally developed as a sound insulation for party walls to bring them into line with the current Building Regulation requirements for sound control, M20AD also makes an excellent answer to flanking noise problems on internal walls. To insulate either a separating wall or an internal structural wall, the installation is the same. M20AD is simply glued to the wall using Sta-Put a special contact adhesive in aerosol form for ease of use followed by two layers of 12.5mm acoustic plasterboard that is glued on top using the same special adhesive.

So, for those of you that have suffered a pre-completion test failure due to flanking noise, use the M20AD solution. For those of you that want to avoid a pre-completion test failure due to flanking noise, use the M20AD solution.

Flanking noise doesn’t have to be a problem anymore.

Written by Stephen Young

© Sound Service (Oxford) Ltd 2003