Sound Insulation Between Dwellings

What This Requirement Covers

Approved Document E requires that walls and floors separating dwellings provide adequate resistance to airborne sound (speech, music, television) and impact sound (footsteps, dropping objects). Poor sound insulation is one of the most common complaints from occupants of new homes and can significantly affect quality of life.

Key Requirements

Performance Standards

The minimum performance standards for separating walls and floors between dwellings are

Separating walls:

1. Airborne sound insulation: Minimum DnT,w + Ctr of 45 dB (pre-completion testing)
2. This means the wall must reduce the transmission of airborne sound by at least 45 dB across the frequency range

Separating floors:

1. Airborne sound insulation: Minimum DnT,w + Ctr of 45 dB
2. Impact sound insulation: Maximum L'nT,w of 62 dB (lower values indicate better performance)

Compliance Routes

Approved Document E provides two compliance routes

1. Pre-completion testing (PCT): Sound insulation is measured in the completed building by a registered testing body. Tests must be carried out on a sample of separating walls and floors before the building is occupied.

1. Robust Details (RDL): The builder registers with Robust Details Ltd and uses approved construction details that have been tested and proven to exceed the minimum standards. Site inspections are carried out by RDL inspectors, and pre-completion testing is not required.

Common Separating Wall Types

1. Type 1 (Solid masonry): Two leaves of dense blockwork with plaster finish; minimum mass 415 kg/m²
2. Type 2 (Cavity masonry): Two leaves of blockwork with an empty cavity; minimum 75 mm cavity width
3. Type 3 (Masonry between independent panels): Masonry core with independent timber or metal stud frames on each side, with absorbent material in the cavities
4. Type 4 (Timber or steel frame): Two independent frames with absorbent material and multiple layers of plasterboard; minimum 200 mm cavity between frames

Common Separating Floor Types

1. Type 1 (Concrete base with soft covering): Concrete floor with resilient floor covering (carpet with underlay)
2. Type 2 (Concrete base with floating floor): Concrete floor with a floating screed or platform floor on resilient layer
3. Type 3 (Timber frame with floating floor): Timber joist floor with resilient layer, absorbent material, and heavy ceiling (multiple layers of plasterboard)

Flanking Transmission

1. Sound can bypass the separating element through flanking paths: external walls, internal walls, and floor/ceiling junctions
2. Approved Document E and Robust Details specify flanking construction requirements for each separating element type
3. Common flanking issues: lightweight external walls, continuous floor screeds across the separating wall, and missing flexible joints

Practical Compliance Tips

1. Decide on the compliance route (PCT or Robust Details) at the design stage; Robust Details has additional costs but eliminates the risk of failing a pre-completion test
2. If using PCT, test early enough in the programme to allow remedial work if results fail
3. Fill all mortar joints in masonry separating walls completely; even small gaps significantly reduce sound insulation
4. Do not bridge the cavity in cavity masonry separating walls with mortar, debris, or wall ties
5. Use resilient bars or independent ceiling systems to improve impact sound performance on separating floors
6. Seal all service penetrations through separating elements with flexible acoustic sealant
7. Floor finishes matter: hard floor coverings (tile, laminate) on separating floors without a resilient layer will fail impact sound tests