The interface between drywall partitions and other surfaces frequently throws up many issues for specialist contractors. In particular, poor design or fitting of a detail could significantly limit or even ruin the acoustic performance of a drywall installation. This process, known as flanking, typically involves the noise finding the path of least resistance. Steve Menary reports.

“When I ran training courses I used to say that sound was like water and found the gaps,” says Greg Fletcher, the Tenon technical manager over at  SIG Interiors, who cautions against naive ambitions amongst some designers over attainable acoustics and subsequently successful interface with drywall.

He adds: “Most people are guided by the brochures but they need to be realistic. If the log data is 40 decibels (dB) on a partition, you won’t get that. That’s not a fault in the system. When products are put through an acoustic test, they are semi sterile conditions and you will never find that on a building site. It’s a tough call to get the installation done to the same level as the test.

“Typically, if the board is installed well against a raised access floor or a suspended ceiling and installed there’s no problem, but if it’s an open void there is a multitude of places that noise can come through like a light fitting. It’s only as strong as its weakest point and you’ll always get a reduced decibles reading through a door-set as most doors have a standard 6mm gap beneath them.”

Identifying that weak point is also essential. Steve Halcrow, Chairman of the British Standards’ committee on plastering and drywall, says: “Another issue is that drywall manufacturers say they have designed a brilliant partition system so you put it in your spec, but then you need to put a door in. So you get the door from someone else, who might have tested the door in a block wall but not necessarily drywall. And once you puncture a wall with a high acoustic rating with a door or window, then you can’t have the same acoustic rating.”

Jim Brennan, managing director of specialist contractor MACS, agrees, saying: “Although partitions have a dB rating that is special to the factory.”

Some moveable partitioning systems can achieve higher ratings with Sektor, the
interior solutions business launched last September, offering systems which provide up to 58dB sound attenuation and fully glazed options reaching 50dB.

Sektor sales director Steve Compton says: “Development in partition joints can additionally provide a completely flush aesthetic, especially when installed alongside frameless offices and doors. In addition to the traditional options for vertical mullions, dry glazed joints can give the appearance that the glass simply butts up against the next pane.”

This allows for a standardisation that is missing from on-site solutions. Although housebuilders have been moving more towards standardisation for years using timber framed housing, but on large scale commercial projects there is no standardisation. As a result, specialist contractors often face many different interfaces through a single major office or hospital project, let alone different projects.

“Standardisation is fine, but architects would buck against that as they want some creativity,” adds Mr Halcrow. “In terms of acoustics, the permutations are often unique to each job that you can’t acoustically test in a lab so the solutions to the problems have to be reinvented each time to cope with different glazing mullions or different walls.

“The issue that you are getting is that you fix the wall to an advanced state then have to take it down again if there’s a problem. The big message is that any interfaces need careful design, it needs to be carefully built and carefully checked.”

Some specialist contractors such as MACS do insist that supervisors individually check each detail. But not all specialist contractors are quite so diligent, particularly in an industry where some operatives have worked in the same manner for many years.

Mr Halcrow says: “As an industry, we are plagued by ‘that’s how I’ve always done it’ philosophy. Then there’s the demon on the other shoulder, the bloke who says ‘I’ve always done it this way for 15 years’ but he’s been doing it wrong.”

Yet specialist contractors also have to work around the workmanship of other trades. Greg Fletcher adds: “You are always at the mercy of the fixers. What should be 6mm might be 10mm but in their defence it’s also the other interfaces they are working with.”

Jim Brennan advocates a more linked-up approach with greater focus on achieving a high acoustic level amongst all the trades that interface with dry-liners.

“It wouldn’t go amiss we all understood the acoustic ratings as well as we do,” adds Mr Brennan.
“At pre-start meetings, we try to go through the acoustics and how important that is to be correct, because the outcome of the acoustic wall failing is unbelievable.”