Part E Acoustic Underlay — What the Building Regs Actually Require
Written by our acoustic insulation specialist — 15+ years experience supplying soundproofing to UK homeowners, developers and contractors. About our experts.
If you're working on a project subject to Part E acoustic building regulations, choosing the wrong underlay can mean failed inspections, costly remedial work, and delays to completion. This article explains what Part E actually requires for floors and which products meet the standard.
What Is Approved Document E?
Approved Document E (ADE) is the UK Building Regulations guidance document covering sound insulation in dwellings. It applies in England and Wales. Scotland follows Section 5 (Noise) of the Building (Scotland) Regulations; Northern Ireland uses Technical Booklet G — both with similar requirements.
ADE covers four types of building elements: separating walls, separating floors, internal walls, and internal floors. For most acoustic underlay projects, the relevant section is separating floors between adjoining dwellings.
Part E Requirements for Separating Floors
| Project Type | Impact (L'nT,w) | Airborne (DnT,w + Ctr) | Testing Required? |
|---|---|---|---|
| New build — purpose-built flats | ≤ 45 dB | ≥ 43 dB | Yes (PCT) |
| Material change of use (conversion) | ≤ 62 dB | ≥ 43 dB | Recommended |
L'nT,w is a field measurement — it includes room geometry effects and flanking transmission paths, which is why field values are typically higher than laboratory ΔLw values. Laboratory results inform design; field results determine compliance.
How Acoustic Underlay Contributes to Part E Compliance
Acoustic underlay alone does not make a floor Part E compliant. Compliance depends on the complete floor assembly: substrate, underlay, floor covering, and ceiling treatment below. However, the underlay is the most critical variable within the floor assembly for impact noise control.
Our recommended Part E products:
6mm Recycled Rubber Acoustic Underlay (74 dB ΔLw)
The most popular choice for Part E projects. At 74 dB ΔLw, it provides maximum impact isolation within the floor assembly. When installed under a floating floor on a concrete separating slab, typical field measurements of L'nT,w 50–60 dB are achievable — well within the conversion threshold of 62 dB and approaching the new-build target of 45 dB with appropriate ceiling treatment.
12mm Acoustic Flooring System (30 dB impact / 58 dB airborne)
For projects requiring maximum performance on both impact and airborne transmission, the 12mm system is the professional's choice. It combines impact resilience with mass for airborne isolation. For separating floors in conversion projects and some new-build configurations, it provides the performance margin needed to pass Pre-Completion Testing with confidence.
Pre-Completion Testing (PCT)
For new-build dwellings, Building Control requires PCT — field measurements by an accredited acoustician — to verify compliance. The number of tests required depends on development size, but typically 1 in 10 rooms must be tested.
PCT results are influenced by:
- Floor assembly specification (underlay, floor type)
- Ceiling construction below (plasterboard, resilient fixings)
- Flanking paths at perimeters
- Workmanship quality
Our performance data is provided in the format required by accredited acousticians. Contact us for technical data sheets suitable for PCT submissions.
Common Compliance Mistakes
- Specifying acoustic underlay but fixing the floor to the subfloor — invalidates the acoustic isolation entirely.
- Fitting rigid skirting boards through the floor — creates flanking paths that can reduce field performance by 10+ dB.
- Using only underlay without treating the ceiling below — necessary for achieving ≤ 45 dB in new-build separating floors.
For Part E projects, contact us for technical support: Acoustic Underlay Range | 6mm Rubber (74 dB) | 12mm System