Prevention of flanking issues in new build apartments
| Client: | Bohunone Building Contractors & Composition Design |
| Location: | Cranleigh |
| Region: | Surrey |
| Sector: | Residential |
The team developing a new build apartment scheme in Surrey approached Hush Acoustics to ensure they could successfully create two apartment blocks to a high acoustic standard, and in particular address the risk of flanking noise.
The Fairhaven development in Cranleigh features two, three-storey apartment blocks, which were constructed using brick and blockwork by Bohunone Building Contractors. One of the buildings 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.
THE CHALLENGE
The architects, Composition Design, sought to address what is a relatively common, but sometimes overlooked, issue in multi-occupancy buildings constructed using brick and block walls with timber joisted floors.
The key issue was not only to ensure that the separating walls and floors were acoustically insulated to levels compliant with Approved Document E of the Building Regulations, but that measures were incorporated to prevent the potential for flanking noise to transmit between properties through the continuous blockwork.
Flanking is the issue of sound bypassing the main sound insulation materials typically integrated into walls and floors. It 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 SOLUTION
To address the flanking issue, Hush Acoustics proposed a combination of floor and wall acoustic treatments. It recommended its HD1013: Hush System 2003 acoustic floor system for all the separating floors within both blocks, plus a wall lining on 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 RESULTS
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.
PRODUCTS USED
HD1013: Hush System 2003
Hush Panel 28
Hush Slab 100
Hush Bar
Hush Bar Deep
Hush Slab 25
