Part E Sound Insulation: Separating Floors and Walls, Pre-Completion Testing and Performance Standards

Summary

Noise between neighbouring dwellings is one of the most common sources of disputes in the UK housing stock. Part E of the Building Regulations addresses this by requiring minimum sound insulation performance in separating elements — the walls, floors and stairs that lie between two different dwellings (whether in separate buildings or in flats above/below each other).

The standard applies to new construction, conversions of existing buildings to flats (material change of use), and rooms for residential purposes (e.g. student accommodation, hotel rooms). It does not apply to existing construction where no building work is being done — but when renovation or extension work affects a separating element, Part E may be triggered.

For builders and developers, the practical challenge is achieving Part E during construction. Common failure modes include flanking transmission (sound bypassing the primary barrier through joist hangers, continuous screed, or gaps at the perimeter), and impact sound in separating floors. Understanding how to avoid these failures, and what to do if pre-completion testing reveals a failure, is essential knowledge.

Key Facts

• Approved Document E — Covers resistance to the passage of sound; 2003 edition with 2004 and 2010 amendments
• Separating wall — Wall between two dwellings; may be solid masonry, timber frame, or steel frame construction
• Separating floor — Floor between two dwellings (one above the other); includes concrete, timber and composite construction
• Airborne sound — Speech, TV, music transmitted through air and structure; measured as DnTw+Ctr (dB)
• Impact sound — Footfall, dragged furniture; measured as L'nTw (dB) — lower is better
• DnTw+Ctr — Standardised level difference weighted with spectrum adaptation term; the primary measure for airborne sound
• L'nTw — Weighted standardised impact sound pressure level; maximum permitted
• Minimum airborne (walls) — 45 dB DnTw+Ctr
• Minimum airborne (floors) — 45 dB DnTw+Ctr
• Maximum impact (floors) — 62 dB L'nTw
• Pre-completion testing (PCT) — Mandatory unless Robust Details used; conducted by accredited test body; typically 1 test per junction per dwelling type
• Robust Details — Approved construction details that can be used in place of testing; requires registration with Robust Details Ltd; specific plot registration fee applies
• Flanking transmission — Sound transmitted via indirect paths (joist hangers, services, masonry continuity); major cause of test failure
• Rooms for residential purposes — Hotels, student accommodation; slightly different target values apply

Quick Reference Table

Detailed Guidance

Understanding Sound Transmission Paths

Before designing or testing, understand how sound travels between dwellings:

Direct transmission: Through the primary separating element (wall or floor). This is what Part E is designed to limit.

Flanking transmission: Sound bypasses the main barrier and travels through connected elements:

• Flanking from floor: where solid floor screed is continuous across the separating wall, vibration crosses
• Flanking from ceiling: where plasterboard ceiling is continuous with ceiling in adjacent flat
• Flanking via joist hangers: metal joist hangers built into a separating wall transmit vibration directly
• Flanking via services: pipes passing through walls and floors
• Flanking through gaps: holes for services not sealed, gaps at wall/floor junctions

Flanking is the most common cause of pre-completion test failures. A perfectly constructed separating wall can fail its test because of a continuous screed or steel joist hanger.

Approved Construction Details for Separating Elements

AD E Appendix A gives approved constructions for new build. The main types:

Separating walls:

Type 1 — Solid masonry:

• Brick or concrete block; minimum 415 kg/m² (dense block) or 300 kg/m² (aerated)
• 2-coat plaster finish both sides; no dry lining that creates void at wall
• No continuous floor screed across wall
• No metal joist hangers built in to wall; use resilient hangers or bear on wall

Type 2 — Cavity masonry:

• Two leaves each minimum 100mm dense block or 150mm aerated; 50mm cavity
• No wall ties that bridge the cavity (use butterfly ties)
• Cavity insulation optional but benefits acoustic performance if fitted

Type 3 — Timber frame with absorbent material:

• Two separate structural frames with gap; mineral wool in cavity
• Each frame independently attached to structure
• Frames must not be structurally connected

Type 4 — Steel frame:

• Similar principles to timber frame; two separate structures

Separating floors:

Type 1 — Concrete base with soft covering:

• 300mm+ precast or in-situ concrete; soft floor covering (carpet) on top
• Ceiling: plasterboard on resilient bars (not direct fix to soffit)

Type 2 — Concrete base with floating floor:

• Concrete base; resilient layer (mineral wool or foam); screed; hard floor covering possible
• 25mm minimum timber batten or screed floating on resilient quilt
• No contact between floating layer and perimeter walls (perimeter strip required)

Type 3 — Timber, combined structure:

• Engineered joists; mineral wool in cavity; resilient floor treatment above
• Ceiling: plasterboard on resilient bars with mineral wool above
• Perimeter isolation crucial

Pre-Completion Sound Testing

When PCT is required:

• All new build dwellings where Robust Details not used
• Conversions where separating elements have been built

Sampling regime (AD E Section 1.5):

• Test 1 set of results per combination of separating element type per development
• Minimum 10% of junctions should be tested (one wall and one floor per set)
• Developer selects which units to test

Who conducts PCT:

• Must be conducted by an accredited test body
• Accreditation via UKAS (for organisations) or ANC (Association of Noise Consultants) member
• Test report issued; building control requires satisfactory results before completion certificate

Test method:

• Airborne: loudspeaker generates pink noise in source room; measurements in receiving room and background; calculate level difference
• Impact: standard tapping machine on floor; measure in room below; calculate standardised level
• Follow ISO 140-4 (field measurements of airborne) and ISO 140-7 (impact sound)

If the test fails: Investigate cause. Common remedies:

• Flanking via joist hangers: add resilient mount or replace with different connection detail
• Continuous screed: break continuity at separating wall base; requires excavation and isolation strip
• Gaps/holes: seal all penetrations with acoustic sealant; maintain fire resistance
• Plasterboard direct-fixed to ceiling: add resilient bars
• Re-test after remediation; must pass before occupation

Robust Details Scheme

The Robust Details scheme provides an alternative to pre-completion testing. Instead of testing, the developer registers individual plots and constructs to the approved Robust Details specification.

How it works:

1. Developer registers each plot with Robust Details Ltd (robustdetails.com)
2. Per-plot fee applies (currently approx. £68 per dwelling)
3. Developer constructs to the specific Robust Detail specification for the chosen wall/floor type (e.g., E-WM-1 for external masonry wall)
4. RDSQ (Robust Details Specialist Quality) system: checks during construction; inspector may visit
5. No PCT required unless RD inspector or building control has reason to believe non-compliance

Advantages:

• Avoids test programme risk
• Faster process for volume housebuilders
• Design certainty upfront

Disadvantages:

• Per-plot registration cost
• Must follow specification exactly; deviations require separate PCT
• Scheme only covers specific approved constructions

Conversions: Material Change of Use

When an existing building (house, office, barn) is converted to flats (material change of use), Part E applies:

• Separating elements must achieve the conversion standard (43 dB airborne, 64 dB impact)
• This is 2 dB lower than new build standard, recognising older construction difficulties
• PCT is required for conversions unless Robust Details or equivalent is demonstrated
• Existing elements that already achieve the standard need not be upgraded
• Challenge: existing timber floors (pre-1920 joists) rarely achieve 43 dB without major treatment

Treatment of existing timber floor for conversion: Options include:

1. Overlay with acoustic floor screed or floating floor deck
2. Add resilient ceiling below (on resilient bars with mineral wool quilt)
3. Combined: floating deck above + resilient ceiling below (best result)
4. Note: flanking through perimeter masonry is very difficult to address in existing buildings — often the limiting factor

Frequently Asked Questions

Does Part E apply to loft conversions within a single dwelling?

No. Part E applies to separating elements between different dwellings. A loft conversion within a single-family house creates a floor between floors of the same dwelling — Part E does not apply (though good practice acoustic treatment is still beneficial). Part E would apply if the loft conversion created a separate flat (separate tenure from the lower floors).

Our separating floor test failed impact sound — what are the cheapest fixes?

The cheapest fix depends on the cause. If the floating floor is correctly installed but there are perimeter contact points (floor touching the separating wall or skirting board through the resilient strip), addressing this can add 3–5 dB at low cost. Adding a soft floor covering (carpet, rubber-backed floor) is often the cheapest route to pass impact tests. A high-quality carpet with good underlay can improve L'nTw by 15–20 dB. If the ceiling below has no resilient mounting, adding resilient bars and an extra layer of plasterboard adds impact performance but at higher cost.

Can I use acoustic plasterboard to comply with Part E?

Acoustic plasterboard (denser, heavier than standard) adds to the mass and therefore improves airborne sound performance. However, it will not by itself achieve Part E performance. Part E compliance requires the whole separating construction to be designed correctly — including flanking control, resilient mounts, and mineral wool — not just a single higher-performance board. Use acoustic plasterboard as one element of a complete Part E solution.

What is the difference between Part E and Part F (ventilation)?

They are entirely separate approved documents. Part E covers sound insulation. Part F covers ventilation and air quality. However, they interact: acoustic sealing of separating elements to achieve Part E can conflict with ventilation requirements; sound-attenuating acoustic ventilators may be needed to satisfy both.

Regulations & Standards

• Building Regulations Approved Document E (2003 + 2004 and 2010 amendments) — Resistance to the passage of sound

• ISO 140-4 — Acoustics: measurement of sound insulation in buildings and of building elements (field airborne)

• ISO 140-7 — Acoustics: measurement of impact sound insulation in buildings (field impact)

• BS EN ISO 717-1 — Acoustics: rating of sound insulation in buildings and building elements — airborne

• BS EN ISO 717-2 — Acoustics: rating of sound insulation — impact sound

• Robust Details Handbook — Approved details for use in lieu of PCT; Robust Details Ltd publication

• GOV.UK Approved Document E — Full text of Part E

• Robust Details — Robust Details scheme; plot registration; approved detail handbook

• Association of Noise Consultants (ANC) — Accredited test body directory

• part k protection — Part K staircase geometry in flat conversions

• plasterboard types — Plasterboard types including acoustic options for Part E solutions