Resilient Bar Centres: Fixing Spacings for Walls and Ceilings Explained

Resilient bar spacing is one of the most important variables in any acoustic separation system – and one of the most commonly misapplied. For ceilings, bars should be fixed at 450mm centres. For walls, 600mm centres is the standard. Where 2400mm boards are being used, centres drop to 400mm to ensure adequate support across the full board length. Get this wrong and the acoustic performance of the system drops significantly, regardless of how good the bars themselves are.

Why Fixing Centres Matter for Acoustic Performance

The whole point of a resilient bar is to decouple the plasterboard layer from the primary structure. The bar flexes under sound pressure rather than transmitting vibration directly into the joist or stud. That decoupling only works properly if the board is adequately supported without being over-fixed. Too few bars and the board sags or vibrates excessively. Too many, and you start creating additional contact points that reduce the isolation effect and increase sound transmission.

In practice, most acoustic failures attributed to resilient bars come down to installation errors rather than product quality. Incorrect fixing centres are one of the most common causes, alongside screws accidentally contacting the structure behind the bar and bars making contact with perimeter walls.

Standard Fixing Centres by Application

Ceiling Applications: 450mm Centres

For resilient bar ceiling systems – the most common application in flat conversions, HMOs, and domestic acoustic upgrades – bars run perpendicular to the joists at 450mm centres. This spacing is consistent with the tested system specifications published by British Gypsum and reflects the structural and acoustic requirements of a standard ceiling build-up using 12.5mm or 15mm plasterboard.

At 450mm centres, a 2400mm board spans across either five or six bars depending on how the layout falls. The perimeter bar should sit no more than 150mm from the wall line to prevent board edge deflection.

Wall Applications: 600mm Centres

On wall applications, resilient bars run horizontally across the face of the studs at 600mm centres. The wider spacing reflects the different loading conditions on a vertical surface – there’s no gravity load on a wall system in the same way there is on a ceiling. 600mm centres remain consistent with tested system performance data for party wall and separating wall build-ups.

As with ceilings, the end bars should be positioned within 150mm of the floor and ceiling lines. Bars should not make contact with the perimeter walls, floor, or ceiling. Any contact at the edges compromises the decoupled layer and creates flanking paths for sound to travel around the system rather than through it.

2400mm Board Lengths: 400mm Centres

When specifying 2400mm boards – which is standard across most UK drylining work – centres reduce to 400mm for both walls and ceilings. The additional fixing point is needed to support the board across its full length without mid-span deflection. At 600mm centres, a 2400mm board would only hit four support points, which is insufficient for a flat, stable finish.

This is a detail that’s easy to overlook when reading fixing centre guidance, since many published specs state the headline figure (450mm ceilings, 600mm walls) without making the board length adjustment obvious. If you’re using standard 2400x1200mm boards – and realistically most jobs are – 400mm centres is the correct working figure for ceilings, and the same applies to wall applications where 2400mm boards are being run vertically.

Fixing the Bars: Key Points

Resilient bars are fixed through the mounting flange into the joist or stud using drywall screws. The critical rule is that the screw must pass through the bar’s fixing flange only – it must not contact the plasterboard or create any hard connection between the board and the structure. This is where a lot of installations go wrong. If a screw is slightly too long and catches the back of the board, or if a bar is fixed through both flanges instead of the mounting flange only, the decoupling is compromised.

Bars should be installed with the open channel facing downward on ceilings and toward the room on walls. Overlapping joints should be staggered – bars should not be joined end-to-end in line, as this creates a continuous rigid path along the ceiling or wall plane.

Spacing Summary Table

What Goes Wrong When Centres Are Incorrect

Installing bars at wider-than-specified centres is the most common mistake. Contractors familiar with plasterboard on timber battens sometimes apply the same logic to resilient bars, spacing them at 600mm on ceilings because that’s what they’d do with a timber batten. The result is a board that spans further than the spec intends, with reduced support and a finish that may show deflection over time – and acoustic performance that falls short of what the system should deliver.

The opposite error – fixing bars too close together – is less common but does occur, particularly when contractors are uncertain and decide that more must be better. Over-fixing increases the number of contact points between the board and structure and reduces the flexibility in the system. The acoustic isolation effect relies on the bar being able to flex. Pack them too tightly and you’re effectively creating a more rigid connection, which is the opposite of the intent.For straightforward domestic jobs, getting the centres right and keeping the bars free from perimeter contact will do more for acoustic performance than almost anything else. You can browse the full range of resilient bars at Online Insulation, including individual lengths and 50-length bulk packs for larger projects. For complete acoustic system builds, the MF ceiling system and metal stud and track ranges are also available if the project calls for a full drylining solution.