Acoustic performance
Acoustic Screed and Flanking Noise Explained
A failed Part E sound test often isn't a screed problem at all — it's noise flanking around the edges through a gap the screed detail was supposed to close.
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Acoustic floors in flats, conversions and party-wall builds depend on more than just an acoustic mat and a floating screed layer above it. If sound tests fail, the cause is very often flanking transmission — noise travelling around the isolated floor through a rigid bridge somewhere at the perimeter — rather than a fault in the screed itself.
This is a genuinely common misdiagnosis. A contractor sees a failed test, assumes the screed build-up is wrong, and specifies a change that doesn't address the actual leak path. Understanding flanking transmission first saves time and cost.
This page covers where flanking paths typically occur around a screed, how we detail against them, and what to check if a test has already failed.
Common flanking paths around an acoustic screed
- Screed bridging the perimeter isolation strip and touching the wall directly
- Skirting fixed through the floating layer into the structural slab below
- Services (pipes, cables) passing rigidly through the isolation layer without a sleeve
- Door thresholds detailed without a break in the floating system
- Acoustic mat compressed or torn during the screed pour, losing its isolating properties
How we detail against flanking transmission
- 1
Continuous isolation strip
A perimeter isolation strip runs unbroken around every wall and column the floating floor meets.
- 2
Mat protection during pour
The acoustic mat is protected from puncture and compression while insulation and reinforcement go down.
- 3
Service sleeving
Any pipe or cable crossing the isolation layer is sleeved so it doesn't create a rigid bridge.
- 4
Skirting detail check
Skirtings are specified to fix to the wall only, never through the floating screed into the slab.
- 5
Threshold detailing
Door thresholds maintain the isolation gap rather than closing it with a rigid strip.
Symptom vs likely cause
| Test result | Likely cause |
|---|---|
| Failed impact sound test, screed itself correct depth | Perimeter isolation bridged somewhere on site |
| Failed airborne sound test | Often relates to the wall/floor junction, not the screed layer |
| Inconsistent results across rooms | Localised bridging — a single skirting fixing or service penetration |
| Consistent failure across all rooms | Systemic detailing issue — isolation strip type or mat spec |
Get your acoustic floor build-up reviewed
Send us the acoustic system spec and any test results and we'll help identify whether the issue is the screed or a flanking path.
Before anyone touches the screed spec, walk the perimeter and check every place the floating layer meets something rigid. That's where flanking noise almost always gets in.
— Exeter Liquid Screeders
Acoustic & Flanking Noise — questions we get asked
Keep reading across the site
Get your acoustic floor build-up reviewed
Send us the acoustic system spec and any test results and we'll help identify whether the issue is the screed or a flanking path.