Flanking Noise

10th August 2024

Understanding Flanking Noise and How to Stop It

What is Flanking Noise?

Flanking noise refers to sound that travels through indirect paths in a building, bypassing the intended soundproofing barriers. Unlike direct sound transmission, which moves straight through walls, floors, or ceilings, flanking noise travels through alternative routes such as structural elements, gaps, or connected spaces. This can significantly reduce the effectiveness of soundproofing measures and create unwanted noise in areas thought to be protected.

Example of a common flanking path in a building

One of the most common flanking paths is between the cavity of a floor and the ceiling in a timber joist floor. You can soundproof your walls to stop direct sound from passing through them, but if you leave the floor cavity untreated, the sound could transfer indirectly through the untreated cavity.

Common paths for flanking sound to transfer through a building

Electrical outlets: Plug sockets and light fittings create a hole in the wall or ceiling.
Floor/ceiling cavities: The cavity between timber joists at the junction of a partition wall.
Doors: Lightweight or poorly fitted doors can be the weak point in a soundproof wall.
Pipework: Pipes and plumbing chased into walls and through floors is a point of weakness.
Shared structural building components: Floor joists, floorboards, concrete slab floors and structural walls.
Gaps and cracks: Sound will easily transfer through small cracks and gaps in any separating structure.

Empty floor cavities create an easy flanking path to transfer sound below or above your soundproofing

empty floor cavities are an easy route for flanking sound

What is the best way to stop the most common flanking noise paths?

How to improve the sound insulation of a building to reduce any flanking paths.

Electrical outlets: Avoid fitting outlets back to back, making direct sound transfer harder. Use an acoustic putty pad inside the back box to ensure the acoustic integrity. Acoustic insulation inside a cavity between the outlet blocks absorbs sound transfer between sockets.
Floor/ceiling cavities: The floor adjacent to the wall is one of the most vital areas for party wall soundproofing. Use 100mm acoustic insulation inside the floor joists to add mass and density and absorb sound that can transfer below or above your soundproofing. Insulate against the wall, coming back into the room 600mm.
Doors: Upgrade your door to improve the sound insulation of internal walls. Most door manufacturers produce fire doors with good acoustic ratings. A cheaper alternative is to use a solid-core door and ensure it is well-fitted to the door frame.
Pipework: Insulate the pipework to reduce noise transfer and seal any gaps where pipework penetrates wall, floor and ceiling junctions.
Shared structural building components: Isolating one part of a building from another by creating a room within a room will stop flanking sound from transferring between shared structural building components. Common methods include floating floors and decoupled walls and ceilings. Using the sound isolation clip AcoustiClip system is the best method of decoupling an acoustic ceiling or wall from the existing structure.
Gaps and cracks: Acoustic sealant ensures the acoustic integrity of the building by sealing gaps and cracks in the structure. Filling gaps with an acoustic sealant between plasterboard edges and the perimeter of walls and ceiling junctions also reduces sound transmission.

Soundproofing materials used to stop flanking noise

Acoustic Putty Pads Single & Double Sockets

£4.35 exc VAT.

Acoustic Sealant 310ml & 900ml

£3.95 exc VAT.

AcoustiClip - Sound Isolation Clip

£4.95 exc VAT.

Acoustic Insulation 100mm DFM Per Pack

£41 exc VAT.

Noisedeck 28 2400mm x 600mm x 28mm T&G Flooring

£29.2 exc VAT.

Conclusion

Flanking noise can be a significant issue in buildings, but it can be effectively minimised with proper understanding and strategic interventions. The key is to address both the structural elements and the smaller gaps and cracks through which sound can travel. By improving structural integrity, sealing gaps, using soundproof materials, and considering design layouts, you can create a quieter and more comfortable environment, free from the disruptions of flanking noise.