Home Features Operable walls:  what you need to know  

Far fewer operable walls are installed on interiors projects than demountable or relocatable partitions, yet the risks involved are exponentially higher.  FIS technical manager Joe Cilia highlights these risks and provides guidance on overcoming them to achieve a successful installation.

The number of operable walls being installed is increasing as their  benefits are being more widely  recognised. With certain sectors, such as education and conferencing, rigid acoustic targets may necessitate an on-site acoustic test to ensure that the product installed performs as required in the specification. This is where one of the greatest risks can be become apparent.

Partition specifications will often refer to dB Rw, whereas specifications for an operable wall may well refer to ‘dB DnTw’. Both are single-figure dB ratings, but the first is a laboratory figure while the second is an on-site figure. Because of flanking, the  on-site Db DnTw figure will always be lower than the dB Rw figure.  This simple difference has the  potential to make a profitable  project go into the red, let alone risk a contractor’s reputation.

“Confusion about performance can be found across the supply chain,” explained David Bolton of Accordial. He added: “There can be a lack of understanding of product types and their performance. Julian Sargent, managing director at Style, commented: “I would be as bold as to state that over 75 per cent of the selection process team don’t really understand the true meaning of the acoustic level, which makes it difficult to select a product.”  Mr Sargent added: “There are even examples where old and  out-of-date certificates are  confusing the market, which is  why we support the FIS Test Certificate Verification Scheme where manufacturers can submit test certificates for verification by an independent acoustician. I think this scheme will give specifiers the confidence to know that the test result is current and verified.”

The additional weight of  operable walls must be considered by a structural engineer as part of the design and specification process, which has to allow for the load to be concentrated in a single point, such as the parking bays and even mid-run. This often requires additional steel work.

Any risk of structure-borne sound transference which could disturb other tenants should be designed out. Some support framework is likely to be installed ahead of a final site survey, so allow sufficient time from survey to installation, as panels will be manufactured with a minimum tolerance to ensure the best sound reduction performance. Airborne sound insulation of an installed  operable wall relies on flanking sound being addressed. Flanking sound is where sound energy can transfer from one space to  another, maybe through gaps in the ceiling and floor void, or because the wall has been installed between two walls of lower performance than the operable wall, or the seals around the panels haven’t been properly set, leaving gaps.

Where an acoustic engineer is involved in the process, a series of  interventions should be designed into the scheme to mitigate the risk. But when there’s no engineer involvement, the operable wall manufacturer should be involved to ensure the products perform as expected. This may also include  recalculating the reverberation in the room if hard surfaces are specified on the operable wall panels.

Unlike demountable or even  relocatable partitions,  operable walls are dismantled and reinstalled on a regular basis, and often by non-specialist staff. This means there is a huge risk of users getting all, or even part, of this process wrong, which can result in poor sound insulation or damage to the panels. Time should always be allowed after completion to train an operable wall champion, and it’s also worth providing an ongoing maintenance proposal.

Operable wall panels can be big and heavy, and often higher than your average plasterboard, so extra attention is required during a site survey to ensure that the panels can be offloaded and carted safely to where they are required.

As with any specialist product, FIS recommends that the  manufacturers are consulted at every stage in the process to reduce risk and ensure the client is completely satisfied. Find out about the FIS Test Certificate  Verification Scheme at  www.thefis.org/specialist- interest-forum/test-certificate- verification-scheme

JOE CILIA
joecilia@thefis.org

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Supplying an operable wall –  what to take into account:

  1. Understanding the specification.
  2. Understanding the requirements.
  3. Considering the implications of the additional load/weight that the wall will put on the structure.
  4. Understanding the acoustic and fire performance requirements.
  5. Ensuring you have correct and verified information from a site survey.
  6. Ensuring that there is a planned ingress route to the final position.
  7. Ensuring there are adequate sound barriers in the ceiling and floor voids.
  8. Ensuring that the products abutting the operable wall are equal to or exceed the performance requirements of the operable wall.
  9. Being aware that a hard surface finish can increase reverberation within a divided space.
  10. Ensuring that a training and maintenance programme is offered when discussing the sale

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