Approved Document E sets the sound insulation that walls and floors between dwellings must achieve in England and Wales. If you are converting a house into flats, building flats, or a building control officer has asked for an acoustic specification, this is the document in question.
Our Sound Insulation Design Report specifies compliant build-ups from $595, in 5 working days.
The numbers
| Situation | Airborne (minimum) | Impact (maximum) |
|---|---|---|
| Conversions — material change of use | 43 dB DnT,w + Ctr | 64 dB L’nT,w |
| New build — purpose built dwellings | 45 dB DnT,w + Ctr | 62 dB L’nT,w |
Higher airborne numbers are better; lower impact numbers are better. Internal walls within a dwelling have a separate, lower requirement, and rooms for residential purposes such as HMOs are covered too.
Two routes to compliance
- Pre-completion testing. Build it, then test a sample of separating elements on site. This is the default route and the one conversions must use.
- Robust Details. For new-build only, register with Robust Details Ltd and build one of their approved constructions exactly as specified, avoiding testing.
A design report supports either route. It does not replace the testing.
Why schemes fail: flanking transmission
Most failures are not caused by the separating element itself. They are caused by sound travelling around it:
- A floor screed continuous across the separating wall
- A ceiling void shared between two flats
- Service penetrations and back-to-back sockets
- Rigid connections between the separating wall and a lightweight external wall
- Joists built into a separating wall from both sides
- Gaps at the wall head, unsealed perimeters, missing mastic
This is why a good design report spends as much space on junctions and workmanship as on build-ups. Specifying a 60 dB wall and then bridging it with a screed gets you a failed test and a rebuild.
What a design report should give you
- Every separating element scheduled and referenced
- Layer-by-layer build-ups, product-agnostic, with named examples
- Junction details for the critical connections
- A flanking strategy, not just element performance
- A workmanship checklist for site
- A testing strategy: how many tests, which elements, when
- A letter your building control body can accept
Working outside England and Wales?
Scotland uses Section 5 of the Technical Handbooks; internationally the equivalents are ISO 717 and ISO 12354 ratings in Europe, and STC and IIC under ASTM E413 and E492 in the US and Canada. We write to whichever applies — tell us in the brief.
If you have already failed a test
It is recoverable, and usually cheaper than people fear once the actual transmission path is identified. Send the test report and the as-built construction, choose the largest tier, and we specify the remedial work.