Improving Sound Insulation

The initial design, the materials and construction system used and the standard of workmanship all play a crucial role in determining the sound insulation performance achieved between adjoining dwellings.

Firstly the level of sound insulation performance required needs to be clearly identified, together with any potential sound transmission paths such that these can be taken into consideration during the design process.
The sound insulation performance of any separating wall or floor is affected by five key factors:

  • Isolation
  • Mass
  • Absorption
  • Resilience
  • Stiffness

A combination of these will determine the sound insulation performance of the partition at different frequencies. However, simply designing and constructing a good separating wall or floor may in itself not be sufficient, as junctions with other parts of the building structure may be equally important. This is due to flanking sound transmission via, for example, the inner leaf of the external wall, the external wall cavity and internal partitions. It is therefore important that the whole construction system be considered and not just the separating partition.

The following sections outline some examples of how poor design and workmanship can lead to reduced sound insulation performance.

Solid blockwork walls:

  • Not laying blocks on their side and full width.
  • Using double coursing of blockwork.
  • Incorrect block density.
  • Mortar beds not sufficiently filled with mortar and/or open joints.

Blockwork cavity walls:

  • Cavity too narrow.
  • Collection of mortar on wall ties.
  • Use of incorrect wall ties (should be type A wall ties, as defined in Approved Document E).
  • Mortar beds not sufficiently filled with mortar and/or open joints.
  • Cavity bridged by floor slabs or steel beams.

Timber frame walls:

  • No insulation in cavity.
  • Gaps at head plate and/or sole plate not sealed.
  • Wall linings not staggered.
  • Sockets located back to back and not well sealed.
  • Excessive bridging between studs.

Precast concrete slab floors:

  • Slab joints not fully grouted and sealed.
  • Slab not built into perimeter walls.
  • Using a slab with too low a mass.
  • Not sealing the small void created by the camber at slab and wall head junction.

Beam and block floor:

  • Not fully filling between beams and over blocks with grout/screed.
  • Gaps left between blocks as blocks not laid tightly enough.
  • Perimeter walls continuous between dwellings.
  • Junction of beam and perimeter wall not sealed well with mortar or grout.

In order to reduce impact sound transmission it is common practice to install a resilient floor surface treatment, commonly termed a floating floor. These can include bonded soft floor coverings, platform floors, flooring screed with isolating layers, resilient battens and resilient cradles. Listed below are some commonly found errors resulting in the performance the floating floor being compromised:

  • Resilient layer torn or damaged due to on-site activities.
  • Incorrect screws or fixings used such that the resilient layer is bridged.
  • Flanking edge strips not used or not installed properly allowing the screed or floor boards to come into contact with perimeter walls.
  • Joints in isolating layer do not overlap.
  • Penetration of isolating layer by pipes, for example for underfloor heating, leading to bridging.
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