Internal walls

Also see:

6.3.7Sound insulation

Walls shall be insulated with materials of suitable thickness and density to provide adequate resistance to the transmission of sound. Issues to be taken into account include:

  1. sound-resisting construction
  2. rooms which contain a WC.

Sound-resisting construction

Masonry separating walls

In England and Wales, separating walls may be built in accordance with Robust Details ‘Resistance to the passage of sound’.

To maintain sound insulation:

  • the correct blocks should be used
  • fully fill joints, mortar beds and perpends
  • use only approved wall ties
  • space wall ties 900mm minimum horizontally and 450mm minimum vertically
  • avoid any reduction in the thickness of masonry
  • ensure spaces around joists are fully filled with masonry and pointed
  • where external cavity walls have blown or pumped insulation, separating walls should be constructed with flexible cavity stops so that insulation cannot enter the cavity
  • care should be taken when specifying dry lining, as the thickness of plasterboard layers, and the methods of sealing and fixing, can affect the transmission of sound
  • holes, voids and hairline cracks should be avoided or made good, as they can significantly reduce the effectiveness of a sound-insulating wall.

In masonry separating cavity walls and where the cavity is up to 75mm, flexible wall ties should be:
■ butterfly type ties, or
■ tested to show compliance with building regulations.

Solid separating walls should be taken through the inner leaf of an external cavity wall and tied. Where the same blocks are used for both walls, tooth bonding is acceptable.

Chases can reduce the sound insulation value of a wall and should:
■ be cut only where specified in the design
■ not be cut using impact power tools where there is a risk of damage
■ not exceed 1/6 of the thickness of the single leaf where horizontal
■ not exceed 1/3 of the thickness of the single leaf where vertical
■ not be chased where hollow blocks are used, unless specifically permitted by the manufacturer
■ be fully filled with mortar
■ have positions of electrical socket outlets staggered on opposite sides of the wall.

Separating walls of framed construction

Separating walls of framed construction should not have gaps in the:

  • mineral wool quilt
  • plasterboard layers
  • fire stopping.

Flanking walls

The construction of the flanking wall and the position of openings should comply with building regulations.

Rooms containing a WC

The guidance below applies in Northern Ireland, Scotland and the Isle of Man. In England and Wales, the construction should comply with building regulations.

A minimum sound reduction of 38dB (100-3150Hz) when tested in accordance with BS EN ISO 140-4 is required between rooms that include a WC and:

  • living rooms
  • dining rooms
  • studies
  • bedrooms, except where the WC is ensuite.

Timber studwork

Timber studwork should be used with one of the following on each side:

  • two layers of 12.5mm plasterboard
  • one layer of 12.5mm plasterboard and 25mm mineral wool between the studs
  • one layer of 9.5mm plasterboard, 5mm skim coat and 25mm of mineral wool between the studs
  • one layer of 12.5mm panel board and 75mm of mineral wool between the studs.

Other forms of studwork construction may be acceptable where the sound reduction is achieved and independent evidence of performance is available.

Where mineral wool quilt is used for acoustic insulation in partitions, it should be of a suitable thickness and density. Where two layers of plasterboard are used, joints should be staggered and properly filled.

Blockwork partitions

Masonry partitions provide adequate sound insulation without additional treatment where:

  • blocks have a minimum density of 600kg/m3 and are finished on both sides with 13mm of plaster, and
  • blocks are tied at every course to adjoining walls, with joints fully filled.

Proprietary partitions

Independent test evidence of the system’s performance is required in accordance with Technical Requirement R3.