Part E Sound Insulation Compliance Engineering

Project background

Environmentally Sound Limited (ESL) were appointed to support a conversion of an existing double-storey dwelling in Wolverton into two separate self-contained flats (one above the other). As a material change of use, the separating construction required appropriate sound insulation performance consistent with Building Regulations Approved Document Part E.

ESL’s engagement focused on engineering the acoustic separation at construction stage — providing practical guidance on how to install the acoustic system correctly and, crucially, how to avoid flanking transmission via structural junctions and cavities.

The problem: flanking transmission in conversions

In many residential conversions, acoustic performance is compromised not by the separating floor system alone, but by flanking paths — sound travelling through party walls, boxed wall cavities, and rigid junctions between ceilings, floors and walls.

• Sound propagation through wall cavities within boxed-in constructions.

• Rigid connections that create structural sound bridges at junctions.

• Incorrect build order that prevents continuous acoustic separation layers.

ESL’s solution: sequence-led detailing using Isomass systems

Lower floor: ceiling first, then party wall, then internal walls

ESL specified a strict construction sequence to ensure the ceiling isolation layer remained continuous and that junctions did not create rigid sound paths.

1. Construct the entire ceiling first across the full footprint beneath the upper flat. Internal walls were not permitted prior to ceiling installation.

2. Construct the party wall next (between the lower dwelling and the entrance passage/stairs), in full height and length, following the ceiling installation.

3. Construct internal walls last, providing separation gaps where internal walls meet the party wall, and sealing the gap with FR sealant to prevent leakage without rigid contact.

Upper floor: floating floor integration and kitchen isolation points

ESL noted that, unlike the lower ceiling, the Isomass floor system on the upper flat could be installed around internal walls without compromising performance, provided junction detailing followed the manufacturer’s guidance.

In the kitchen, ESL specified installation details for cabinetry including the locations of Isomass Impacta pads to reduce impact noise transmission from fixed units.

Outcome

• Acoustic performance was engineered into the build through explicit sequencing and junction control.

• Flanking transmission risks were addressed at source, reducing the likelihood of post-completion non-compliance caused by detailing errors.

• Contractors and inspectors received clear, buildable instructions aligned with proprietary system requirements.

Note: This case study summarises construction-stage compliance engineering and detailing. It does not reproduce confidential client data or measured test results.

Why Environmentally Sound Limited (ESL)

Many acoustic failures in residential conversions occur despite using recognised products, because junctions and build sequencing create sound bridges. ESL provide engineering-led compliance support — translating acoustic principles into practical site instructions that contractors can follow.