Sound insulation is not the first thing most homeowners think about when planning a house extension – but it is something that building regulations address directly, and in certain circumstances it can have a real impact on how your extension needs to be designed and built. Part E of the Building Regulations covers resistance to the passage of sound, and while it is most closely associated with new-build properties and flats, it also applies to some house extension scenarios that are worth understanding before work begins.
At Simply Extend, we factor Part E requirements into our designs wherever they are relevant – which is more often than many homeowners expect, particularly for semi-detached and terraced properties.
What Does Part E of the Building Regulations Cover?
Part E sets minimum standards for sound insulation between different parts of a building and between dwellings. It covers two types of sound:
- Airborne sound – voices, music, television, and other sound transmitted through the air and through building elements such as walls and floors
- Impact sound – noise transmitted directly through the structure of the building, such as footsteps on a floor above
Part E specifies minimum performance levels for sound insulation, measured in decibels, that building elements must achieve. For walls separating dwellings, the standard is a minimum of 45 dB DnTw (airborne sound insulation). For floors, the standard is 45 dB DnTw for airborne sound and a maximum of 62 dB L’nTw for impact sound.
When Does Part E Apply to House Extensions?
Extensions Involving Walls Shared with a Neighbouring Property
The most common scenario where Part E is directly relevant to a house extension is where the extension shares a wall with the adjoining property – the party wall. This arises in semi-detached and terraced houses where the extension is built against or close to the boundary shared with a neighbour.
Where the extension itself incorporates a new section of separating wall – for example, a side return extension that creates a new wall alongside the neighbouring property – that wall must be designed to meet Part E standards for sound insulation. Simply building a standard single-leaf block wall may not achieve the required performance. Party wall constructions used in extensions typically involve a cavity wall or a wall with an acoustic lining, and the junction with the existing party wall must be carefully detailed to avoid flanking transmission – where sound bypasses the main wall by travelling through connected elements.
Rooms Above Existing Living Space
Another scenario where Part E is relevant is the addition of living space above an existing room – for example, building a first-floor extension above an existing single-storey ground floor room. The floor between the new room above and the room below must achieve the required airborne and impact sound insulation performance. This typically means incorporating acoustic insulation within the floor construction and using appropriate ceiling linings.
This is not just about keeping the household’s noise under control – the regulations require the floor to perform to a defined standard, which must be demonstrated to building control.
Conversions of Existing Buildings
Part E also applies where an extension or conversion changes the use of a space – for example, converting a garage into a habitable room that adjoins the main house. The walls and floors separating the new habitable space from the rest of the dwelling, and from any neighbouring property, must meet the required standards.
Pre-Completion Testing
One aspect of Part E that sometimes comes as a surprise is the requirement for pre-completion testing in certain circumstances. Where an extension involves a new separating wall between dwellings – such as a party wall extension that creates new sections of the shared wall – building control may require acoustic testing of the completed wall to confirm that it meets the required performance standard before a Completion Certificate is issued.
This testing is carried out by a specialist acoustic tester and involves measuring the actual sound insulation performance of the completed construction. If the wall fails to meet the standard, remedial works will be required before the certificate can be issued. Specifying the wall construction correctly at the design stage – and ensuring it is built correctly on site – is therefore essential.
In practice, pre-completion testing is most commonly required for new-build properties and conversions. For extensions, whether testing is required will depend on the specific nature of the works and the position of the local building control body. Your building control officer can advise on whether testing is required for your specific project.
What About Noise from the Extension Itself?
It is worth noting that Part E is not concerned with noise from mechanical equipment – extractor fans, heating systems and the like – which is a separate consideration. Part E is focused on the acoustic performance of the building fabric. However, good practice in designing a comfortable, quiet home will also consider the location and specification of mechanical services to minimise noise nuisance.
Flanking Transmission
One of the most technically complex aspects of sound insulation in practice is flanking transmission – where sound travels around a well-specified wall or floor via connected elements. A wall may achieve excellent airborne sound insulation in isolation, but if it is connected to a floor or another wall through which sound can travel freely, the overall performance will be compromised.
Managing flanking transmission requires careful attention to the design and construction details at junctions between building elements. This is particularly important at the point where a new extension wall meets an existing party wall, and where new floors connect to separating walls. At Simply Extend, our designers are experienced in specifying construction details that address flanking transmission, not just the primary wall or floor element.
Why Part E Matters
Sound insulation can have a real impact on the quality of life in a home – both for the occupants of the extended property and for their neighbours. Poor sound insulation through a party wall means that conversations, music and television from the adjoining property are clearly audible in your new room, and vice versa. An extension that looks fantastic but fails to provide adequate acoustic separation from a neighbour is a disappointment that is expensive to fix after the fact.
Getting the acoustic specification right at the design stage – and ensuring it is built correctly on site – is the most cost-effective approach. At Simply Extend, we treat sound insulation as a design consideration from the outset, not an afterthought.
Planning an extension and want to make sure everything is covered? Get in touch with Simply Extend today for a free site survey and expert advice. Call us on 0800 917 7571 or email info@simplyextend.co.uk and one of our team will be happy to help.
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