Approved Document E (Sound Insulation): What Homeowners Need to Know

Part E sets minimum performance standards for:

• Airborne sound insulation — measured in decibels weighted (DnTw + Ctr). The minimum for walls between dwellings is 45 dB; for floors it is 45 dB.
• Impact sound insulation — measured as L’nTw. For floors between dwellings the maximum (lower is better) is 62 dB.
• Rooms used for residential purposes — such as student accommodation and care homes — have similar requirements.

These are the minimum values that must be achieved by physical testing (pre-completion testing, or PCT) unless a ‘Robust Details’ construction is used.

Part E applies when you:

• Convert a house into two or more flats — the new separating floors and walls must meet the performance standards.
• Build an extension to a semi-detached or terraced house — any wall or floor that becomes a new separating element between dwellings must comply.
• Convert a commercial building to residential — all new separating elements must meet Part E.

Part E does not require you to upgrade existing party walls and floors when you are simply extending within your own home, unless those elements are being materially altered.

There are two ways to demonstrate Part E compliance:

• Pre-completion testing (PCT) — an acoustic engineer tests the finished separating walls and floors with specialist equipment to show the performance standard is achieved. This costs roughly £300–£700 per test.
• Robust Details (RD) — a scheme that allows certain pre-approved construction details to be used without testing. You register the dwelling with Robust Details Ltd (fee approximately £51 per dwelling) and follow the RD specification precisely. Building control will inspect to confirm the specification has been followed.

Robust Details is generally simpler and cheaper for standard new-build construction; PCT is required when a non-standard construction is used.

For a house-to-flats conversion, typical sound-insulation approaches include:

• Separating floor: a floating floor (resilient layer + chipboard) on top of the existing floor, plus an independent suspended ceiling below (e.g. two layers of 15 mm plasterboard on resilient hangers). This can add 100–200 mm to the floor thickness.
• Separating wall: an independent leaf of masonry or a double-stud timber frame wall, isolated from the existing structure to prevent flanking transmission.
• Flanking paths — sound travels through connected structure as well as directly through walls and floors. Junction details (e.g. at floor/wall junctions) must be designed to minimise flanking.

If you are using Robust Details, building control will inspect the construction at key stages to verify the specification is being followed. Critical checks include the resilient layer type and thickness, plasterboard layers, and the absence of penetrations that would break the acoustic seal.

If using PCT, an acoustic engineer will test after completion but before any soft furnishings are added. If the test fails, remedial work is required before a completion certificate can be issued.