So, what Causes Sound Test Failures in Flats? here are the top issues we see in London and the South East. Sound test failures in London flats are extremely common — especially in conversion projects, where the original structure was never designed to meet modern acoustic standards. Older timber floors, lightweight partitions, and poor workmanship all contribute to under‑performance during Approved Document E (Part E) sound insulation testing.
Below are the most frequent causes of failure, why they happen, and how to avoid them on your next project.
1. Poorly Installed Acoustic Insulation
One of the biggest causes of airborne sound test failure is incorrectly fitted insulation within separating floors or walls.
Common issues include:
- Insulation slumped at the bottom of joists
- Voids or missing sections
- Low‑density insulation used instead of acoustic‑grade mineral wool.
For guidance on correct build‑ups, see: Designing for Sound Insulation
2. Gaps Around Perimeters and Service Penetrations
Sound travels through the weakest point in a structure. In London flats, we frequently find:
- Unsealed gaps around floor perimeters
- Holes around pipes, sockets and cable penetrations
- Gaps behind skirting boards
- Open voids around steel beams or joist ends
- Fireplace openings that have not been sealed properly.
These gaps act as flanking paths, allowing sound to bypass the main structure entirely.
A single 5mm gap running along a floor perimeter can reduce airborne performance by up to 10dB.
For a full breakdown of required testing types, see: What Types of Sound Insulation Testing is Needed on Flats?
3. Lightweight Floor Finishes Without Acoustic Underlay
Impact sound failures are extremely common in London flats, especially where:
- Laminate flooring
- Engineered timber
- LVT
- Tiles
all of the above installations can fail, if they haven’t been installed without a high quality acoustic underlay.
Hard finishes transmit footfall noise directly into the structure, causing high impact levels in the flat below.
Typical reasons for failure:
- No resilient layer beneath the floor
- Incorrect underlay (thermal, not acoustic)
- Underlay installed incorrectly
- Floating floor not isolated from walls
For more detail, see: Sound Testing Floors in Flats
4. Bridging Between Structural Elements
Bridging occurs when two parts of a structure that should be acoustically separated are accidentally connected.
Examples include:
- Resilient bars screwed directly into joists
- Floating floors touching perimeter walls
- Acoustic hangers installed incorrectly
- Ceiling joists touching partition walls
- Plasterboard fixed through resilient layers
Bridging creates a rigid path for sound transmission, often causing both airborne and impact failures.
5. Incorrect Build‑Ups in Conversions
Many London conversions start with separating floors that only achieve 30–35dB airborne performance — far below the 43dB minimum required under Part E.
Common problems include:
- Thin timber joists
- No insulation between joists
- Single plasterboard ceilings
- No resilient layers
- Historic construction with voids and gaps
Without proper acoustic upgrades, these floors cannot pass testing.
APT strongly recommends sample sound testing before works begin to determine the correct upgrade strategy.
For methodology details, see: Pre & Post Construction Sound Testing Methodology
6. Lightweight Masonry (Thermalite Blockwork)
Lightweight masonry—particularly Thermalite and other aircrete blockwork systems—is one of the most frequent causes of sound insulation test failures in commercial and residential developments. Although these blocks offer excellent thermal performance and are easy to handle on site, their low mass makes them acoustically weak. Under Approved Document E, separating walls must achieve minimum airborne sound insulation values, and lightweight blockwork often struggles to meet these requirements without additional treatment.
- Aircrete blocks typically have a density of 400–600 kg/m³, far below the mass needed to resist airborne sound transmission effectively.
- Mortar joints are inconsistent or poorly filled
- Chases for services are cut too deeply
- The blockwork is not fully bonded at junctions
- Flanking paths are present via floors, ceilings, or adjoining walls
Lightweight masonry can pass sound testing, but only when supported by the right construction details and acoustic upgrades. APT’s acoustic design review helps to identify weak points early, as well as containing recommendations to reduce the risk of costly failures at the final testing stage.
Foe more details please see the reasons for party floor failing the sound insulation testing
How to Achieve a Sound Insulation Test Pass First time
To achieve a first‑time pass:
- Use acoustic‑grade insulation (45–60kg/m³)
- Seal all gaps with acoustic mastic
- Avoid lightweight masonry
- Install resilient bars correctly
- Use acoustic underlays beneath hard floors
- Avoid bridging at all costs
- Follow a proven acoustic build‑up
- Undertake pre‑completion checks before testing
APT can review drawings, inspect site installations, and provide targeted advice to ensure compliance.
Recommended Reading
Here is some good articles on sound testing in London Flats, we hope it helps.
- What Types of Sound Insulation Testing is Needed on Flats?
- Designing for Sound Insulation
- Sound Testing Floors in Flats
- Sound Testing & Acoustic Design for Lease Conditions
Why Use APT Sound Testing?
APT Sound Testing is one of the UK’s leading acoustic consultancies, offering:
- UKAS‑accredited testing laboratory status
- ATTMA Level 2 certification
- 22 years’ experience in acoustics and sound insulation testing
- Specialist expertise in London and South East developments
- Fast attendance, often within 24–48 hours
- Same‑day certification
- Combined services including air testing, thermal imaging and diagnostic smoke surveys
- In‑house sound test engineers — no subcontractors
Our experience means we can identify issues quickly, provide practical solutions, and help ensure your project passes first time.
Contact Us
For sound insulation testing of flats in London and the South East, or for help with acoustic design:
APT Sound Testing
Email: Info@aptsoundtesting.co.uk
Phone: 07775623464
Web: www.aptsoundtesting.co.uk
We can usually attend site within 24–48 hours, and certificates are issued same day.