Pass Your Sound Insulation Testing

Noise flanking or sound flanking is a sound that transmits between spaces indirectly, going over or around, rather than directly through the main separating acoustic element. This can allow sound to transmit between spaces even though the main separating element itself provides good acoustic insulation.

Flanking noise or sound is defined as sound from a source room that is not transmitted via the separating building element e.g. the wall or floor partition. The sound is transmitted indirectly via paths such as external walls, windows, doors and internal corridors or where construction elements are not isolated as resulting in indirect or flanking noise transmission.

Pass Your Sound Insulation Testing

One of the most popular reasons for excessive flanking noise and potential sound test failure in apartment blocks is due to the use of lightweight blocks within the inner perimeter construction. The lightweight blockwork acts like a large snare drum allowing sound to travel straight up and across the inner perimeter wall from one unit to the other. Even if you have used an acoustically robust party wall or floor partition there is a high chance the sound insulation testing may still fail. If you have used lightweight blocks in your onsite construction and the building subsequently fails the sound insulation testing, you may need to construction an independent lining throughout the inner perimeter wall; this should provide some isolation and mass to reduce the chance of noise flanking.

Invariably, sound will usually find the easiest noise transmission path through construction materials. For instance, construction workers sometimes run lightweight inner envelope walls straight through the whole elevation. Unfortunately, even though acoustically robust walls may be pulled of the inner envelope, it doesn’t stop sound travelling from unit to unit via the continuous perimeter wall. In this instance the party wall should run straight through to the back of the cavity and the perimeter wall should abut the party wall. This will provide a continuous cavity and a break in the perimeter wall.

Typical Sound Flanking Pathways are as follows:

  1. Dividing Floor Partitions – through Floor and Floor Joist Space (if insulation has not been installed or direct fixing to joists without a drop ceiling below the partition under test)
  2. Dividing Ceiling Partitions – above and Through the Ceiling Space (where an adequate acoustic break has not been carried on through the ceiling void)
  3. Shared Building Components – floor Boards, Floor Joists, Continuous Drywall Partitions, Continuous Concrete Floors, and Cement Block Walls.
  4. Plumbing Chases – within walls & floor slab should be filed with mortar etc. to add mass to this weakened area
  5. Via Electrical Fixtures – Light Switches, Telephone Outlets, and Recessed Lighting Fixtures (if penetrations have been cut back to back with the opposite dwelling under test)
  6. Via Structural Steel – structural steel beams are often a major cause of noise transmission as it may run through separate dwellings and plasterboard is often fixed directly to the steel without sound breaks.
  7. Through Windows – if they are single glazed and are in close proximity to separate dwellings within the building envelope, and do not have secondary glazing as a minimum.
  8. Structural Joints – perimeter and movement joints should be filled with acoustic mastic.
  9. Small gaps or air paths – seal all perimeter and party wall/floor partitions with sealant.

To reduce the chance of noise flanking transmission, the acoustic design should be considered at the initial design stage of the project. Good design detailing will minimise the chance of noise flanking and should help the project pass its sound insulation testing negating the need for expensive remedial treatments at the end of the project.

Pass Your Sound Insulation Testing

We can advise on all types of acoustic design, whether it’s accomplished during initial construction or during a refurbishment/renovation project. We also undertake UKAS accredited sound insulation testing, providing a ‘one stop’ solution for all your acoustic requirements.

If you would like more information in regards to sound insulation testing and/or acoustic design advice, then please call us now at or call us on 07775623464. Alternatively please visit our website at

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