Part E Building Regulations Explained – Sound Insulation for Builders & Contractors

What Is Part E?

Part E of the Building Regulations deals with resistance to the passage of sound.

Its purpose is to provide reasonable protection against unwanted sound passing between:

• Houses
• Flats
• Rooms for residential purposes
• Different rooms within dwellings
• Certain spaces within schools

For builders and developers, Part E most commonly affects the design and construction of:

• Separating walls
• Separating floors
• Internal walls
• Internal floors
• Flanking junctions
• Building conversions
• New dwellings
• Schools

Part E should not be confused with a general rule saying that every external window must achieve a particular acoustic dB rating.

The Quick Answer

Part E is mainly concerned with sound insulation between spaces.

For example:

• One flat and another flat
• One terraced house and another
• Bedrooms and other rooms within dwellings
• Hotel or hostel rooms
• School spaces

External windows and doors may still require acoustic performance, particularly on noisy sites, but that requirement will usually come from:

• Planning conditions
• Acoustic consultant reports
• Environmental noise assessments
• BS 8233 design recommendations
• Project specifications

rather than from a single universal Part E window rating.

What Types of Sound Does Part E Consider?

Part E principally considers two broad forms of sound transmission.

Airborne Sound

Airborne sound includes:

• Speech
• Television
• Music
• Traffic-like sound within adjoining spaces

The sound travels through the air and causes walls, floors or other construction elements to vibrate.

Impact Sound

Impact sound is created by physical impact on a building element.

Examples include:

• Footsteps
• Furniture movement
• Objects being dropped

Impact performance is particularly relevant to separating floors.

Separating Walls

Walls between adjoining dwellings need sufficient resistance to airborne sound.

This commonly affects:

• Semi-detached houses
• Terraced houses
• Flats
• Apartments
• Residential conversions

The complete wall construction matters.

It is not enough simply to specify acoustic plasterboard.

Performance can depend on:

• Wall mass
• Cavities
• Insulation
• Independent linings
• Junctions
• Sockets
• Penetrations
• Flanking construction

Separating Floors

Separating floors may need to control both:

• Airborne sound
• Impact sound

Floor construction can therefore include combinations of:

• Structural floor
• Acoustic layers
• Resilient layers
• Floating floor systems
• Suspended ceilings
• Acoustic insulation

The exact construction should follow the designed Part E specification.

Current Performance Standards

Approved Document E gives minimum performance standards for relevant separating constructions.

For purpose-built dwelling-houses and flats, the guidance includes an airborne sound insulation target of 45 dB DnT,w + Ctr for relevant separating walls and floors/stairs, with a maximum impact sound level of 62 dB L’nT,w for relevant separating floors and stairs.

For dwellings formed by material change of use, the airborne value shown is 43 dB DnT,w + Ctr, with a maximum impact level of 64 dB L’nT,w for relevant floors/stairs.

These are building-performance values, not glass-only Rw figures.

Why This Matters

A common mistake is comparing:

Part E DnT,w + Ctr

with:

Glass Rw

as if they are the same thing.

They aren’t.

Rw

Typically describes laboratory airborne sound insulation of a product or element.

DnT,w

Describes measured sound insulation between rooms/spaces, corrected for reverberation conditions.

The complete building construction affects the result.

Pre-Completion Sound Testing

Part E introduced pre-completion sound testing as a route for demonstrating compliance on relevant new dwellings and conversions.

Approved Document E also recognises Robust Details as an alternative route for certain new-build separating constructions where the applicable requirements are met.

Builders should establish early whether the project uses:

• Pre-completion testing
• Robust Details
• Another approved design route

What Are Robust Details?

Robust Details are approved separating-wall and floor constructions intended to provide reliable acoustic performance when built correctly.

The critical phrase is:

when built correctly.

Even a proven acoustic wall can fail if site workmanship creates sound paths.

Flanking Transmission

Sound does not only travel straight through a separating wall or floor.

It can travel around it through adjoining construction.

This is called flanking transmission.

Potential routes include:

• External walls
• Floors
• Ceilings
• Roof spaces
• Structural frames
• Service penetrations

A good separating wall can therefore still perform badly if its junctions are poorly detailed.

Where Do Windows Fit Into Part E?

External windows usually do not form the separating wall between two dwellings.

Therefore there isn’t a simple Part E rule saying:

“All windows must achieve Rw 40 dB.”

However, window openings can influence the acoustic performance of the overall external façade.

On noisy developments, the acoustic consultant may specify:

• Particular glass Rw
• Rw + Ctr
• Acoustic trickle vents
• Acoustic louvres
• Enhanced frame performance

This is related to the overall acoustic design rather than being a universal Part E window requirement.

Windows in Internal Separating Construction

Where glazing forms part of an internal acoustic partition or separating construction, its acoustic performance becomes much more directly relevant.

The complete partition should be assessed.

Do not simply match the glass Rw to the wall rating and assume the whole partition achieves the same result.

Acoustic Doors

Doors are often the weakest point in an acoustic partition.

A high-performance wall with an ordinary lightweight door may provide poor overall performance.

Where acoustic doors are specified, consider:

• Door leaf construction
• Frame seals
• Threshold seals
• Perimeter gaps
• Glazing
• Ironmongery

The whole doorset matters.

Schools

Part E also covers acoustic conditions in schools.

The current Approved Document refers school acoustic design to Building Bulletin 93 for relevant performance standards.

This is particularly relevant when supplying windows and doors to:

• Schools
• Nurseries
• Teaching buildings

where acoustic specifications may exceed normal domestic requirements.

Conversions

Part E can become particularly challenging when converting:

• Offices to flats
• Houses into multiple flats
• Commercial buildings into residential accommodation
• Hotels or hostels

Existing construction may not have been designed to provide modern separating sound insulation.

Upgrades may be required.

Service Penetrations

Common acoustic weak points include:

• Electrical sockets
• Pipe penetrations
• Ductwork
• Recessed boxes
• Gaps behind skirting
• Ceiling penetrations

Small gaps can substantially reduce acoustic performance.

Common Part E Mistakes

Mistake 1 – Thinking Part E is mainly about external windows

It isn’t.

Mistake 2 – Comparing glass Rw with Part E room-to-room performance

They are different measurements.

Mistake 3 – Building the correct wall but ignoring junctions

Flanking transmission can destroy performance.

Mistake 4 – Putting sockets back-to-back

This can create an acoustic weakness.

Mistake 5 – Changing the Robust Detail construction

A seemingly minor site change can undermine the recognised detail.

Mistake 6 – Leaving sound testing until the end

If the building fails, remedial works can be disruptive and expensive.

Real-World Example

A developer converts an office building into six flats.

The new separating walls look substantial.

However, the original concrete floor and façade provide flanking paths around the new partitions.

Pre-completion testing identifies poor performance.

The problem is not necessarily the plasterboard wall itself.

The complete acoustic junction design needed consideration before construction.

What Should Window Contractors Ask?

Where windows or doors are being supplied on an acoustically sensitive project, ask:

• Is there an acoustic consultant’s report?
• What Rw is required?
• Is Rw + Ctr specified?
• Is the figure for glass or complete window?
• Are acoustic ventilators required?
• Are there planning noise conditions?
• Are internal acoustic doors/screens required?

Do not simply quote:

“acoustic glass.”

Frequently Asked Questions

What does Part E cover?

Resistance to sound transmission in relevant dwellings, flats, rooms for residential purposes and schools.

Does Part E state a minimum dB rating for every external window?

No.

What is airborne sound?

Sound transmitted through the air, such as speech or music.

What is impact sound?

Sound generated by physical impact, such as footsteps on a floor.

What does DnT,w mean?

It is a building acoustic measurement used for sound insulation between spaces.

Is Rw the same as DnT,w?

No.

What are Robust Details?

Approved high-performance separating wall/floor designs that can provide an alternative to pre-completion testing on eligible new-build projects.

Do conversions need Part E?

Relevant material changes of use can trigger Part E requirements.

Does Part E apply to schools?

Yes. The Approved Document references school acoustic performance standards.

Related Guides

• Acoustic Glass Explained
• Laminated Glass Guide
• Trickle Vent Regulations
• Part F Explained
• New-Build Window Regulations
• Building Control Checklist

Trade Tech Technical Support

If your project has an acoustic specification, send us the consultant’s report rather than simply asking for:

“soundproof windows.”

We can then identify the relevant:

• Glass performance
• Window performance
• Ventilator requirements
• Safety/security requirements

before manufacture.

Important: Part E principally concerns sound insulation of building constructions. External façade/window acoustic requirements are project-specific and should follow the acoustic design or planning requirements where applicable.