Building Regs Part E and Acoustic Dry Lining: Airborne vs Impact Sound, STC Ratings and Separating Wall Systems

Summary

Part E applies to new dwellings (including conversions) and material change of use. If you are converting a house to flats, building a new semi-detached or terrace, or constructing rooms in a flatted development, Part E compliance is required. The Approved Document E sets out two compliance routes: the Robust Details route (pre-approved systems requiring no pre-completion testing) and the performance testing route (design to standard, then test before handover).

Drylining plays two distinct roles in Part E compliance. First, as a separating element itself — an entirely drylining separating wall can achieve Part E compliance if designed to the correct system. Second, as an upgrading lining applied to an existing wall or ceiling to improve its acoustic performance — common in conversions where the existing structure does not meet the standard.

Acoustic performance is affected by far more than just the partition itself. Flanking transmission — sound travelling around the separating element through junctions, floor, wall, and ceiling connections — frequently accounts for the failure of otherwise well-specified systems. The most common cause of Part E failures at pre-completion testing is flanking, not the separating element itself.

Key Facts

• Approved Document E covers dwellings; commercial requirements are in Part E volume 2 or BS 8233
• Airborne sound (walls) — Dn,T,w minimum 45 dB (higher = better insulation)
• Airborne sound (floors) — Dn,T,w + Ctr minimum 45 dB
• Impact sound (floors) — L'n,T,w maximum 62 dB (lower = better; impact sound is measured as noise transmitted, not insulated)
• Robust Details scheme — pre-approved wall and floor types that meet Part E without pre-completion testing; requires annual subscription and correct registration; use RD mark on Building Notice
• Pre-completion testing — acoustic test required before occupation; must be conducted by an accredited laboratory (UKAS)
• Separating wall (Type 1) — solid masonry; (Type 2) cavity masonry; (Type 3) masonry/concrete core with drylining; (Type 4) timber or metal frame
• Separating floor (Type 1) — concrete base; (Type 2) concrete base with soft floor covering; (Type 3) timber frame; (Type 4) concrete base with floating floor
• Flanking transmission — sound travelling around the separating element; controlled by: cavity barriers, perimeter seals, correct junction details, no gaps in construction
• STC (Sound Transmission Class) — US rating system; not used in UK Building Regulations. Use Rw or Dn,T,w for UK compliance.
• Rw — laboratory-measured weighted sound reduction index; used for product data
• Dn,T,w — field-measured in situ performance; always lower than Rw due to flanking
• Acoustic quilt — 50–100mm unfaced mineral wool in stud cavity; essential for performance; do not substitute with thermal insulation
• Resilient bar/channel — decouples board from stud; increases performance by 8–15 dB; mandatory in high-specification systems
• Perimeter sealant — acoustic mastic at all junctions; often overlooked; a 1mm gap reduces performance by several dB

Quick Reference Table

Detailed Guidance

Separating Wall Types and Drylining

Type 3 — Masonry with Drylining This is the most common drylining-based separating wall. A 100mm blockwork core (minimum 415 kg/m² mass) is lined with independent drylining on both sides. The drylining must be fully independent — no mechanical connection to the blockwork — with a residual cavity of at least 25mm maintained between the back of the board and the face of the block.

Typical build-up:

• 100mm dense aggregate block (415 kg/m² minimum; 140mm preferred)
• 25mm residual air cavity
• 70mm metal stud lining (CW70 at 600mm centres)
• 50mm acoustic quilt in stud cavity
• 2 × 12.5mm Gyproc WallBoard (or 15mm FireLine for combined fire requirement)
• Overall thickness: ~250mm

This system is registered as a Robust Detail (E-WM-11 series) if constructed correctly. See the Robust Details Handbook for the specific E-WM number that matches your construction.

Type 4 — Timber or Metal Frame Used where structural masonry is not available. Achieving Part E with a pure drylining/metal stud separating wall requires:

• Twin stud construction: two separate rows of studs with a gap between (25mm minimum); studs must not touch
• Heavy board mass: typically 2 × 15mm or 3 × 12.5mm per side
• Resilient channels between studs and boards
• Complete acoustic quilt fill
• Perimeter seals at all junctions

Twin stud systems are challenging to achieve Part E without pre-completion testing. Robust Details type E-WM-21 covers steel frame separating walls — verify your specific build-up against the RD handbook.

Upgrading Existing Walls and Ceilings

In conversions, the existing structure often does not meet Part E. A drylining lining can be added to improve performance. The key metric is:

Improvement needed = required performance − existing performance − flanking allowance

A typical solid brick wall (225mm) achieves approximately 45–50 dB Rw in the lab but only 40–43 dB Dn,T,w in situ (flanking). Adding an independent lining with acoustic quilt can improve by 8–12 dB, sufficient to reach 45 dB Dn,T,w.

Lining specification for upgrading:

1. Independent metal stud lining (minimum 25mm residual cavity behind board to back of stud)
2. Fill stud cavity with 50mm acoustic quilt
3. Minimum 2 × 12.5mm board or 1 × 25mm SoundBloc
4. Seal all perimeters with acoustic mastic
5. Do not bridge the lining to the existing wall (no ties, no plasterboard clips touching the substrate)

Flanking Control Details

Flanking is the main reason acoustic systems fail. Control it by:

At the floor junction:

• Separating wall continuous from floor slab to structural soffit (not ceiling void)
• Or cavity barrier at ceiling level if separating wall does not extend to soffit
• No floating floor running under the separating wall

At the ceiling junction:

• Acoustic ceiling lining to underside of floor above in each apartment
• Resilient hangers between ceiling and structure
• No service penetrations running between apartments without fire and acoustic stopping

At external wall junction:

• Extend separating wall insulation to external wall face
• Avoid lightweight construction at flank walls (a single leaf of lightweight blockwork can flank enough to fail a test)

Services:

• Back-to-back sockets in separating walls: offset horizontally by minimum 150mm, or use back-box acoustic enclosures
• Pipes: wrap plastic pipes in acoustic pipe wrap; avoid running drainage pipes on separating walls if possible

Pre-Completion Acoustic Testing

Pre-completion tests are conducted by a UKAS-accredited laboratory using standardised test methods (BS EN ISO 16283-1 for airborne, BS EN ISO 16283-2 for impact). The test is done in the finished building, with furniture removed, on a representative number of dwelling pairs.

Requirements:

• Test every set of dwelling pairs unless using Robust Details (which requires no test but registration and compliance)
• One failed test means remediation and re-test before occupation
• Results must be included in the building control completion documentation

Common failure reasons (in order):

1. Flanking through floor/ceiling junctions not constructed to detail
2. Missing or incorrectly applied perimeter sealant
3. Resilient bar or acoustic ceiling not installed to specification
4. Services creating acoustic bridges
5. Substituted materials (e.g. thermal quilt instead of acoustic quilt)

Frequently Asked Questions

What is the difference between Rw and Dn,T,w?

Rw is a laboratory measurement of a partition's sound reduction — tested under controlled conditions with no flanking. Dn,T,w is the field measurement in the actual building — it includes flanking transmission. Rw is always higher than Dn,T,w. A partition might have Rw = 55 dB but only achieve Dn,T,w = 47 dB in situ. For Building Regulations Part E, only Dn,T,w counts — never use Rw figures to claim compliance.

Do I need acoustic testing for a loft conversion in an existing house?

No, if it remains a single dwelling. Part E applies when you create new dwellings or new material changes of use (e.g. converting a house to flats). A single loft conversion in one house does not trigger Part E. However, if the loft conversion creates a self-contained unit with habitable space, it may trigger Part E depending on the use class. Consult building control if unsure.

Can I use the Robust Details scheme for conversions?

The Robust Details scheme covers new dwellings (new builds and some conversions). For house-to-flats conversions, a subset of RDs applies — check the Robust Details handbook. Not all RD types are approved for conversion work. If your construction does not match an approved RD exactly, you must test.

What acoustic quilt should I use?

Use an unfaced mineral wool specifically sold as acoustic quilt — typically 50–100mm, 10–30 kg/m³ density. Do not use thermal insulation (e.g. foil-faced PIR or glass wool thermal batts) as acoustic quilt — the material type and density matter. Rockwool RW5 and Isover Party Wall Roll are commonly specified products. Check the specific British Gypsum or Knauf system data for the specified product.

Regulations & Standards

• Building Regulations Approved Document E (England and Wales, 2003, amended 2015) — sound insulation of walls and floors between dwellings

• Robust Details Handbook (current edition, available by annual subscription) — pre-approved construction types

• BS EN ISO 16283-1:2014 — field measurement of airborne sound insulation

• BS EN ISO 16283-2:2015 — field measurement of impact sound insulation

• BS EN ISO 717-1:2013 — acoustic rating: single number values for airborne sound insulation

• BS EN ISO 717-2:2013 — acoustic rating: single number values for impact sound insulation

• BS 8233:2014 — guidance on sound insulation and noise reduction for buildings (non-residential)

• Robust Details Ltd — scheme registration, current handbook, and compliant construction types

• Approved Document E — GOV.UK download

• British Gypsum White Book Acoustic Section — tested system performance data

• Association of Noise Consultants — directory of UKAS-accredited acoustic testers

• british gypsum systems guide — system reference numbers and board performance data

• acoustic ceiling systems — ceiling systems for floor impact and airborne sound control

• building regs part b fire lining — combining fire and acoustic requirements

• metal stud partition installation — installation details that affect acoustic performance