
Noise Assessments – March to June 2020 – Recent Work
Our work these past few months in conducting noise assessments and building acoustic design all over the UK and beyond.
COVID-19:
We remain open, providing a full range of noise assessment and building acoustic design services
The aim of our articles are to break down acoustic terms and concepts as simply as possible, without going too far into the mathematics and every nitty gritty technicality, that acousticians usually love to get stuck into.
So please, if you’re an architect, contractor, developer, planner… or really anyone who occasionally needs to dabble in acoustic design and assessments… then read on…
Is there an acoustic, noise, or vibration related topic or problem that you would like explained? Send us an email and we’ll write an article about it.
There are many sets of Building Regulations requirements which a new or refurbished residential development must meet. One of these, is to achieve a minimum standard of sound insulation performance internally between dwellings. This is an important regulation, as we seek some level of sound privacy from our neighbours, ensuring we can live and sleep in peace.
The specific acoustic performance requirements for new builds and conversions are set within Approved Document E ‘resistance to the passage of sound’, as shown in the table.
Requirement E1 – on-site airborne sound insulation performance targets for separating (party) walls and floors
Separating Element | Airborne sound insulation DnT,w + Ctr dB (minimum values) | Impact sound insulation L’nT,w dB (maximum values) |
Purpose built dwelling-houses and flats (new build) | ||
Walls | 45 | – |
Floors and Stairs | 45 | 62 |
Dwelling-houses and flats formed by material change of use (refurbishment) | ||
Walls | 43 | – |
Floors and Stairs | 43 | 64 |
Purpose built rooms for residential purposes (new build) | ||
Walls | 43 | – |
Floors and Stairs | 43 | 62 |
Rooms for residential purposes formed by material change of use (refurbishment) | ||
Walls | 43 | – |
Floors and Stairs | 43 | 62 |
Approved Document E classes ‘rooms for residential purposes’ means a room, or a suite of rooms, which is not a dwelling-house or a flat and which is used by one or more persons to live and sleep and includes a room in a hostel, a hotel, a boarding house, a hall of residence or a residential home, but does not include a room in a hospital or other similar establishment used for patient accommodation. |
As shown above, the criteria for refurbishments are slightly more lenient than for new builds. This recognises that it can be more difficult to soundproof an existing structure if it cannot be replaced, compared to implementing a construction from scratch.
This relates to sound insulation internally, between residential properties which share a separating wall or floor. It relates to separate properties, not internal walls/floors within a dwelling, which carry a much lower requirement for sound insulation which is not subjected to sound testing.
Standards for noise ingress from outside (i.e. road traffic) are not covered under ADE and the Building Regulations, with the local planning authority having more of an input into what they consider to be a suitable internal noise level target.
Airborne sound insulation relates to sound that travels via the air and through separating structures between rooms. For example, airborne sound across a lightweight floor would pass through the plasterboard ceiling, into the floor void, through the floorboards and into the room. It relates to noise sources such as speech, music, television sound…any noise source that radiates into the air, rather than directly into the structure.
The DnT,w + Ctr relates to a level of on-site sound insulation. In simple terms, put a noise source in one room (the ‘source room’), measure the noise level, then go next door (the ‘receiver room’) and measure again, then calculate the difference. Well actually, this would be a ‘D’. A Dw is similar, but with the ‘w’ denoting a weighting across frequency which accounts for the way humans perceive different frequencies. A DnT,w is a Dw which is then ‘normalised’ to account for the reverberation time of the room (the ‘nT’), recognising that the level difference is dependant on how reverberant the receiver room is, and that every room will have a slightly different reverberation time, hence we need to normalise the result to assess every sound test on a level playing field against a fixed target. A DnT,w + Ctr then adds the addition of a low frequency correction (the ‘Ctr’), as low frequency noise is difficult to control and therefore the regulations add this correction to improve the standard of sound insulation against low frequency noise such as music.
Confused? Let’s look at it really roughly. Take a source level in one flat of 100 dB(A), then a receiver level in the neighbouring flat of 55 dB(A), the level difference is 45 dB, hence our sound insulation performance should be somewhere in the region of 45 dB DnT,w + Ctr…
The higher the DnT,w + Ctr, the better the level of airborne sound insulation.
Impact sound insulation relates to noise generated by actual impact on a structure. Hence this typically is only assessed for intermediate floors, to consider noise such as footsteps, chair scrapes and any other object being dropped or impacting on the floor.
The L’nT,w is determined from measuring sound levels within a room where the floor above is being excited by an impact. Your acoustic consultant will use what’s called a ‘tapping machine’ to do this, which drops a series of weights/hammers on the floor in regular succession at a fixed force (as if the acoustic engineer varied the force every time they test, they’d get completely different results!).
The lower the L’nT,w, the better the level of impact sound insulation.
Airborne sound insulation tests are conducted by placing a loudspeaker, or two loudspeakers in the ‘source’ room. These loudspeakers play white or pink noise at a very high amplitude, to the tune of 95 – 110 dB(A) within the room (the acoustic engineer will be wearing hearing protection!). The reason for using this type of noise, is that it is constant in amplitude, with an even spread of sound energy across frequency, keeping our test nice and consistent. The engineer will use their sound level meter to make a series of measurements in the source room. They will then go to the adjacent room (with the loudspeaker still on) and take a series of measurements within the ‘receiver’ room.
Sets of tests in flats with a separating floor and a separating wall |
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One set of tests should compromise 6 tests (4 airborne, 2 impact): • 1 airborne test across a wall between (where possible) a pair of living rooms • 1 airborne test across a wall between (where possible) a pair of bedrooms • 1 airborne and 1 impact test across a floor between (where possible) a pair of living rooms • 1 airborne and 1 impact test across a floor between (where possible) a pair of bedrooms |
![]() | Sets of tests in flats with separating floors but without separating wallsOne set of tests should compromise 4 tests (2 airborne, 2 impact): • 1 airborne and 1 impact test across a floor between (where possible) a pair of living rooms • 1 airborne and 1 impact test across a floor between (where possible) a pair of bedrooms |
Sets of tests in dwelling-houses with separating walls but no separating floors |
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One set of tests should compromise 2 tests (2 airborne): • 1 airborne test across a wall between (where possible) a pair of living rooms • 1 airborne test across a wall between (where possible) a pair of bedrooms |
I hope you enjoyed this short article, and keep an eye out for more articles on the common questions that I get asked by clients in my job as an acoustic consultant. Feel free to connect and message me through LinkedIn, send me an email at chris@parkerjonesacoustics.com, or through our Contact Us page.
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