Part E Sound Insulation: What You Need Between Dwellings

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Last reviewed: March 2026

What Part E is

Part E is the soundproofing bit of Building Regulations. It's about stopping noise passing between homes, between rooms in the same home, and around common areas in blocks and HMOs.

The aim is "reasonable resistance to sound" - not recording-studio quiet, but enough that normal living noise from next door or the flat above doesn't drive people mad.

This guide is a summary to make Part E easier to use on site. It does NOT replace Approved Document E: Resistance to the passage of sound (current edition).

You must read and follow the full Approved Document E and any acoustic design for your project.

This guide is written for England. Wales, Scotland and Northern Ireland have their own versions of building regulations - the principles are similar but the documents and approval routes differ, so check local requirements if you're working outside England.

Where it applies on your jobs

Part E bites on:

• New-build houses and flats - separating walls and floors between dwellings must hit the Part E performance standards.
• Conversions into flats and HMOs - turning a house into flats/bedsits or adding "rooms for residential purposes" (HMOs, student lets) triggers sound-testing and stricter separating construction.
• Loft conversions - new floors over party walls, and sometimes treatment to existing party walls/roofs.
• Internal layouts - sound control between bedrooms/WCs and other rooms inside a dwelling.
• Common parts in blocks - reverberation in stairwells, corridors and lobbies.

Key "trigger points" - what matters on site

Separating walls and floors between dwellings / HMOs (E1)

• Walls and floors that separate one dwelling/room from another (e.g. semi-detached party wall, flat-to-flat floor) must achieve the airborne and impact sound performance levels in Part E.
• Typical minimum airborne sound insulation between homes is around 45 dB in new build and 43 dB in conversions - the acoustic design will target or exceed this.
• Part E splits sound into:
  • Airborne (voices, TV).
  • Impact (footsteps, doors slamming, stuff dropped on floors).

Internal walls and floors within a dwelling (E2)

• Internal walls between bedrooms or rooms with WCs and other rooms, and internal floors, must give "reasonable resistance" to sound - usually means some mass and insulation, not hollow echo boxes.
• Stud walls to bedrooms and WCs should be built with the right board and often acoustic insulation in the cavity; flimsy 63 mm studs with one layer of thin plasterboard and no insulation are asking for trouble.

Reverberation in common parts (E3)

• In blocks and HMOs, common corridors, stairwells and lobbies must not be overly echoey - finishes should absorb some sound.
• Hard surfaces everywhere (tiles, bare plaster, concrete) in stair cores make noise harsh - you may need acoustic ceilings, wall panels or softer finishes.

Loft conversions and existing party structures

• New loft floors and any work to party walls must not make sound transmission worse than before - the principle is "don't downgrade separating elements".
• Often you'll need resilient bar ceilings, acoustic mineral wool in joists, and sometimes extra layers of board to meet Part E when adding a habitable storey.

Sound testing vs "Robust Details"

• Most new builds and flat/HMO conversions need pre-completion sound tests on a sample of separating walls/floors.
• In some new-build cases, you can use registered Robust Details to avoid testing - but then you must build exactly to that detail; no creative tweaks.

Quick reference table - common jobs

Converting a house into 4 flats or HMO

• All new separating walls and floors between flats/rooms must meet Part E airborne and (for floors) impact performance.
• Expect an acoustic design: resilient bars, acoustic mineral wool, multiple layers of board, and possibly floating floors.
• You'll normally need sound testing before sign-off.

Loft conversion in a semi-detached

• New floor over the party wall must be detailed so sound doesn't flank across (e.g. floor deck breaking onto party wall).
• May need acoustic treatment to the existing party wall and new floor (mineral wool between joists, resilient bars, extra plasterboard).
• Local Building Control "easy guides" often spell out minimum loft sound treatments - worth following.

New-build pair of semis

• Party wall construction must match either a Robust Detail or a tested build-up from the design - block type, cavity, insulation and board layers all matter.
• Party floors in stacked layouts (e.g. flats) need both airborne and impact control.
• You'll either:
  • Build to Robust Details and skip testing, or
  • Build to a specific spec and pass pre-completion sound tests.

Upgrading floor between flat and shop below

• Floor build-up may need extra mass, resilient layers and ceiling upgrades to improve airborne and impact performance.
• Penetrations (services, downlighters) and flanking paths around beams can kill performance if not detailed properly.

Internal re-plan in a house with new en-suite

• Internal walls between bedrooms/WCs and other rooms should have decent sound insulation - e.g. 12.5 mm board each side on studs with acoustic mineral wool.
• Don't cut back to the minimum and leave bedrooms backing onto hollow, uninsulated stud walls for cost-saving.

Routes to compliance for trades

Use Approved Document E and/or Robust Details as your pattern

For separating walls/floors between dwellings, either:

• Follow a Robust Detail exactly (if the designer has chosen one), or
• Follow an acoustic specification and pass testing at the end.

For internal walls/floors, follow AD E examples - boards, studs and insulation types/thicknesses.

Coordinate with an acoustic consultant where needed

HMOs, complex conversions, and mixed-use buildings often benefit from an acoustic consultant to set the build-ups and details.

They'll specify insulation densities, board types, resilient layers and how to deal with flanking paths - follow that spec, don't "value engineer" it on the fly.

Build for sound, not just for looks

Key principles:

• Add mass (heavier layers),
• Add separation (resilient bars, floating floors, double studs),
• Add absorption (acoustic mineral wool),
• Avoid gaps/bridges (seal edges and penetrations).

A couple of missed sealant beads or hard-fixed boards through resilient bars can be the difference between pass and fail.

Expect and plan for sound testing

On non-Robust Detail jobs, allow time and budget for sound testing.

Don't cover up critical ceilings/walls until you're confident the build-up matches spec; failures mean re-work, not an argument over the microphone.

Who is responsible for what

On a typical domestic/HMO project:

• The designer/acoustic consultant is responsible for specifying the separating and internal constructions to meet Part E (or selecting suitable Robust Details).
• The builder/main contractor is responsible for building exactly to that spec - right products, right densities, correct fixings, no unauthorised shortcuts.
• Dryliners, floor fitters and M&E trades are responsible for not wrecking acoustic performance with shortcuts:
  • No unnecessary downlighters in separating ceilings,
  • Services grouped and sealed properly,
  • No "helpful" extra fixings straight through resilient layers.
• The client/owner ends up with noise complaints and failed tests if it's not done properly.

Blunt version:

If you ignore the acoustic spec and just whack in "whatever plasterboard was on the wagon", you'll either fail testing or saddle the client with a noisy building. Either way, you're the one getting the phone call.

Simple rule to drum into your team

If a wall or floor is between dwellings, flats, or HMO rooms, or between bedrooms/WCs and other rooms, treat it as a Part E element. Don't change build-ups, cut out insulation or add holes without checking the acoustic knock-on.

On-site checklist (Part E)

Before you start

• Identify all separating walls/floors (between dwellings/rooms) and all acoustic internal walls/floors (bedrooms/WCs to other rooms).
• Confirm whether you're following Robust Details or a project-specific acoustic spec, and get the details for each junction.
• Clarify with Building Control how many sound tests are expected and when.

While you're working

• Install the correct insulation (thickness and density), boards (type and layers) and resilient components exactly as specified.
• Keep services and downlighters out of separating elements where possible; if they must go in, follow the acoustic detail.
• Seal all perimeter gaps and penetrations with acoustic sealant or approved methods - no gaps left "for the decorator".

When you finish

• Check visible build-ups match the spec/Robust Detail before closing in.
• Arrange and pass sound tests where required; fix any failures properly, not with token patches.
• Keep test certificates and as-built details with the job record for HMO licensing or future sale.

Sources

Based on:

• Approved Document E: Resistance to the passage of sound (2003 edition with 2004, 2010, 2013, 2015 amendments).
• Planning Portal and building-control summaries of Part E for dwellings, flats, HMOs and internal sound control.
• Industry and acoustic-consultant guidance on meeting Part E in practice: Robust Details, sound testing, and typical separating/internal build-ups.

This guide was last reviewed March 2026. SiteKiln does not provide legal, financial or tax advice. All content is for general information purposes only. Always seek professional advice for your specific situation.

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