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
■ be staggered on each side of the wall to avoid them being back to back.

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 construction should comply with building regulations, including the recommended sound reduction between rooms that include a WC and:

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


To achieve the required level of sound reduction, 75mm timber studwork or 45mm steel framing should be constructed with either:

  • two layers of 12.5mm plasterboard (each sheet 10kg/m² min) on each side, with joints staggered and filled
  • one layer of 12.5mm plasterboard (each sheet 10Kg/m² min) on each side, with joints staggered and filled and 25mm unfaced mineral wool (10kg/m³ min) between the studs

Other forms of studwork construction may be acceptable where in accordance with the guidance in supporting documents to the building regulations or where independent evidence of performance is available.

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 or 12.5mm plasterboard, 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.

Sound insulation of soil pipes in floor voids and SVPs

All soil pipes running horizontally through a floor void above or below a habitable room should be wrapped in at least 25mm of mineral wool (10kg/m³ min) and be adequately supported to avoid contact with the floor decking or ceiling.

Sound insulation should be provided to soil pipes passing through homes by an encased boxing, using material (15kg/m²) and wrapping the pipe with a minimum 25mm of unfaced mineral fibre (10kn/m³ min). The insulation should be continued through the thickness of each sound-insulating floor).