Reducing flanking noise risk in new build apartments in Surrey

Hush Acoustics helped the developer of a new build apartment scheme in Surrey to deliver high quality homes which are highly insulated against the risk of flanking noise from the properties below and above.

Composition Design, the architects tasked with designing the two, three-storey apartment blocks in Cranleigh, approached Hush to advise on what is a relatively common, but sometimes overlooked, issue in multi-occupancy buildings constructed using brick and block walls with timber joisted floors.

In addition to ensuring the separating walls and floors were acoustically insulated to levels compliant with Approved Document E of the Building Regulations, measures were incorporated to prevent the potential for flanking noise to transmit between properties through the continuous blockwork.

Flanking can be a major issue in buildings created with masonry walls and timber joisted floors because of the lightweight blocks and large voids which are characteristic of this type of construction method, particularly in walls of continuous brick and blockwork for the full height of the building.

This can result in a noise issue so significant that projects of this kind are highly susceptible to sound test failures due to flanking. Hence why the architect sought specialist guidance from Hush Acoustics at an early stage.

The Fairhaven development features two apartment blocks, which were constructed by Bohunone Building Contractors. One of the blocks incorporates three 2-bedroom flats, and the other provides four 2-bedroom flats and one 1-bedroom property, all designed and built with a traditional brick and tiled roof exterior to complement other properties in this established residential area.

To address the flanking issue, the HD1013: Hush System 2003 acoustic floor system was used for all the separating floors within both blocks, and a wall lining was specified for the inside of any masonry walls that rise up continuously to the full height of the building.

The wall lining consisted of the Hush Bar Deep resilient bars, Hush Slab 25 acoustic insulation slabs and a single layer of 15mm SoundBloc acoustic plasterboard. It was applied to all of the separating walls of the first floor properties, mostly single sided but double sided on those that are most susceptible to flanking, as well as the walls between any flats and the communal stairway.

The HD1013 acoustic floor system consists of a floating floor created using Hush Panel 28, a 19mm plasterboard plank and Hush Slab 100 absorbers within the voids between the timber joists. Hush Bar resilient bars are then attached to the joists to provide acoustic separation, to which two layers of plasterboard are then screwed to form the ceilings – one being a layer of 15mm Fireline and the other a 12.5mm SoundBloc.

Both the wall and floor acoustic systems were sealed at the perimeters to further prevent flanking noise.

Once approved by the architect, the systems were installed by the building contractor under supervision from Hush Acoustics to ensure all the components and materials were fitted in accordance with its guidelines.

The performance was confirmed by the pre-completion sound test. It recorded airborne sound levels as high as 60 dB DnT,w+Ctr for the party walls, demonstrating far higher acoustic performance than the minimum of 45 dB required under Approved Document E.

The party floors were found to perform equally well, recording levels as low as 49 dB DnT,w+Ctr for airborne sound and 51 dB L'nT,w for impact sound. The latter also represents a significant improvement compared to the minimum compliance level of 62dB or lower stipulated by the Building Regulations.

As the Fairhaven project demonstrates, early design consultation is key to addressing the potential for flanking noise and reducing the risk of sound test failures further down the line. If flanking is not considered and treated in the floor/ceiling or wall design and the building fails a sound test, the cost and disruption associated with remedial work could be extremely high.