Approved Document E Explained: Sound Insulation Rules

"We'll sort the soundproofing at the end" is one of the more expensive sentences in residential construction. Approved Document E sets specific, testable decibel thresholds for sound insulation between dwellings, and missing them after the walls are closed up is far costlier than designing for them from the start.

What the actual figures are

For new-build separating walls and floors between dwellings, Approved Document E requires airborne sound insulation of at least 45 dB DnT,w + Ctr, and for floors, impact sound insulation of 62 dB L'nT,w or lower. Airborne insulation measures how well a wall or floor blocks sound like voices and music; impact insulation measures how well a floor blocks structure-borne sound like footsteps.

Where a dwelling is created through conversion or material change of use rather than new build, the bar is slightly more lenient in recognition of the constraints of existing structures: 43 dB DnT,w + Ctr for airborne insulation, and 64 dB L'nT,w or lower for impact. It's still a hard requirement, just calibrated to what's realistically achievable when you're working within an existing building rather than starting from foundations.

Within a single dwelling, internal walls and floors carry their own, separate minimum of 40 dB Rw, a lower bar than between-dwelling separation, but still enough to matter for anyone converting a room into a home office or media room.

Why airborne and impact are tested separately

These two figures don't move together. A wall or floor can perform well against airborne noise, voices, television, music, while performing poorly against impact noise, footsteps, dropped objects, dragged furniture, because the physical mechanisms are different. Airborne sound needs mass and sealed junctions to block it; impact sound needs decoupling, resilient layers that stop the vibration reaching the structure in the first place. A specification that only addresses one will fail on the other.

When pre-completion testing is required

For most new-build separating walls and floors, pre-completion testing by a suitably qualified tester is a Building Regulations requirement, not an optional check. The test happens before completion, which means a failure discovered at that stage means remedial work on a finished building, exactly the expensive scenario that early specification is meant to avoid.

Why it applies to more projects than people expect

Loft conversions, extensions with a habitable room adjoining a neighbour, and hotel guest room separation all fall under the same principles, even when the project doesn't feel like "new residential construction." Assuming a conversion sits outside Building Regulations is one of the most common and costly misjudgements we see.

Common questions

Does Document E apply to a loft conversion? If the work creates or affects a separating structure between dwellings, or between habitable rooms, yes. It's a frequent oversight on conversion projects specifically.

What's the difference between DnT,w and Rw? DnT,w is a field measurement taken on the completed building; Rw is typically a laboratory rating for the product or construction build-up alone. Building Regulations compliance is judged on the field figure.

Checking whether your project needs it

See our guides to hotel acoustics and residential acoustics, or book a free survey to find out which figures apply to your project.