Acoustic targets are often set as a requirement in specifications and contractor requirements in fit out contracts, but are they really understood and what are the risks of getting it wrong? Steve Menary reports.

Acoustics is a key area of overlap between fit out contractors and specialists working on packages. What is often an area of contention between designer and contractors, acoustics also has the potential to be costly.

“Acoustic specifications are a set of requirements and if contractors do not understand them, it could cost them a lot of money,” says Joe Cilia, technical manager at AIS FPDC.

Part of the problem for both fit out contractors and specialists has often been varying standards across the industry. On some projects, such as schools and where there is residency, such as homes, hotels and student accommodation sound insulation and reverberation times can be measured on site, with costly consequences to the contractor if they don’t meet the targets.

Education remains a major growth area and the issue of acoustics is seen as vital to the successful delivery of a project. Knauf technical services manager Mandeep Bansal says: “There is a clear link between poor acoustic performance and children suffering educationally; you can hardly learn what you have never heard.”

Section 1 of Building Bulletin 93 (BB93) covers specification of acoustic performance in education projects. Targets are laid down to achieve acoustic conditions that ‘facilitate clear communication of speech between teacher and student and between students and do not interfere with study’.

Complying with BB93 is central to meeting Part E4 of the Building Regulations but the regulation has become outdated. “Education design has changed a lot since 2003 when BB93 was published,” says Andy Parkin, a partner at Cundall Acoustics, who has been working on a revision that has been in the pipeline since 2009.

Consultation finally began in March 2014, but central government has insisted that any changes to BB93 must not add an extra layer of cost and savings must be demonstrated. The new standard includes changes to areas such as indoor ambient noise level and reverberation time in sports halls.

The Institute of Acoustics held a consultation event on the new standard in April and AIS FPDC has responded, after lengthy discussions with its members.

To ensure effective acoustics, Joe Cilia at AIS FPDC describes four key ways of controlling sound; A,B,C and D; absorption, blocking, covering (or masking) and diffusion, which is commonly used in auditoria. Used in harmony under the direction of an acoustician, they can help to provide an acoustic environment to allow for specific functions of collaboration, concentration or communication.

Controlling external noise can be beyond the remit of the fit out team. Yet external noise can be useful in spaces where privacy is important. The notion of introducing noise to improve acoustic performance seems strange. But this is far from unheard of in the commercial sector. “Some people put white noise in,” says Steve Crompton, sales director at partition supplier Sektor, to help provide privacy where no background sound exists, such as out of town and greenfield developments or where no air handling units are installed which would normally provide a degree of background sound.

Andrew Jackson, marketing director at interior products manufacturer SAS International, agrees. He says: “The best acoustic performance to achieve what is termed ‘Speech Privacy Potential (SPP)’ can involve a degree of background noise and you’ve got to make sure that the space works properly.” This concept is explained in more detail in the ‘Guide to Office Acoustics’ which was published by the association last year.

Clients’ interpretation of acoustic success can differ, says Joe Cilia. To explain the concept of sound masking he adds “At 2:00am in the morning, when there’s no traffic or birds and someone puts a milk bottle down on a door step you can hear it four streets away, but in the middle of the day you can’t even hear it on the same street; that’s how sound masking works. It’s not unusual for a brief to say they want it sound proofed, but what they really want is privacy.” And understanding SPP can be one way of achieving it.

Another of the key acoustic areas addressed in the AIS FPDC guide is sound flanking, which is where sound finds the weakest point in a construction; usually these are voids behind lining or cladding systems, or voids above a partition in the ceiling that damages the acoustic performance. Service penetrations like pipes and ducts and even plug sockets can also have a huge impact on the performance of a partition.

John Butler, technical services director at specialist contractor London Drywall, says: “The issues you get around the perimeter can be a huge area of acoustic weakness. Getting a detail that looks good and meets the acoustic standard is a nightmare and one that we encounter on most projects.”

To meet acoustic standards, baffles or barriers in the cavity are a typical solution but need careful detailing at specification and installation to have the right impact.

Steve Halcrow from AIS FPDC says: “If cavity barriers in floor and ceiling voids are badly installed, they achieve nothing. The design needs to be right. It depends on how much design responsibility that the specialist contractor has. If they are going to commercially take the risk, they need to understand what they are getting into and to understand the whole process and how acoustics work.”

In acoustics, like so many parts of the construction industry, cost, risk and supply chain co-operation remain at the heart of successful delivery.

AIS FPDC will shortly be launching an online training module designed to explain some of these issues and educate site operatives on the relevant things to look out for during installation.