Setting noise limits and thresholds for construction sites is essential to protect the well-being of workers, nearby residents, and the environment. Regulations should be established based on the specific characteristics of each site, considering factors such as proximity to residential areas, time of day, and type of construction activities. Monitoring and enforcing these limits is crucial to ensuring compliance and minimizing the impact of noise pollution on the surrounding community. – if you are unsure about these, contact your local Sonitus Systems distributor for expert guidance: https://www.sonitussystems.com/contact/distributors.
Collaboration between developers, local authorities, and residents is key to finding a balance that allows for necessary construction works to be undertaken, while maintaining a healthy and peaceful living environment for residents and visitors to the area.
What are the noise limits and where do they come from?
Noise limits and thresholds for construction sites vary by country and are typically regulated by local authorities or environmental agencies. For example, in the United States, the Occupational Safety and Health Administration (OSHA) sets guidelines for noise exposure limits in construction sites, while in the United Kingdom, the Control of Noise at Work Regulations establishes limits for noise levels. It is important for construction companies to adhere to these regulations to protect the health and safety of workers and nearby residents.
Generally, noise limits, if regulated, tend to be consistent worldwide since the perception of construction noise pollution is universally similar. Even in the absence of regulations, setting thresholds can greatly assist developers in averting complaints and, in severe cases, lawsuits. Moreover, thresholds and the general measurement of noise data can aid in the development of other noise mitigation strategies such as absorption, blocking, and covering. Focusing on noise control at the source, utilizing barriers and enclosures, and applying operational measures to lower noise levels can significantly alter the impact – and the perceived impact – of the local noise locally. Clearly communicated noise limits and thresholds enable more responsible and considerate construction practices, ensuring regulatory compliance and lessening environmental and community impact.
As mentioned, regulations can play a significant role in minimizing the impact of noise from construction activities. The UK, for instance, has advanced documentation and regulations to manage noise pollution. These standards can be extremely useful for countries lacking such regulations, as they are founded on the human perception of noise as well as the mathematical and scientific principles of noise energy. For example, the UK standards are detailed in the below documentation and is the guidance to which UK professionals manage noise related to construction projects.
- BS 5228-1: 2009 Code of Practice for noise and vibration control on construction and open sites
What is a decibel anyway?
A decibel is a unit of measurement that quantifies sound intensity or electrical signal power. It employs a logarithmic scale to compare a signal’s power level to a reference level, where a higher decibel count signifies a louder sound or a stronger signal.
Perception of decibel levels can differ based on individual sensitivity to sound and exposure to various sound levels. Typically, a higher decibel level means a louder sound, which might be seen as more intense or bothersome. Factors like the distance from the sound source and exposure duration also affect our perception of decibels.
Noise that is considered unpleasant or unwanted is termed a nuisance, such as construction noise or loud music. When such noise exceeds the ambient or background noise, it becomes a nuisance to the listener, which can be expressed in decibels according to the below summary.
- 1dB above ambient noise; barely perceptible
- 3dB above ambient noise; double the energy, just perceptible
- 5dB above ambient noise; clearly noticeable
- 10dB above ambient noise; significantly noticeable and likely to be become nuisance
The following image illustrates how different decibel levels are perceived by humans.
Figure 1: Comparative Noise Levels dB(A)
Setting noise limits
Determining noise limits and thresholds involves judgement, as these are largely influenced by the construction project’s location and the pre-existing noise conditions. Sites with lower ambient noise levels may experience more significant adverse effects compared to those with higher ambient noise. Guidelines such as BS 5228 provide direction on this matter. Noise assessments and thresholds serve three primary purposes:
- For Environmental Impact Assessments (EIA) of major projects, where compensation for rehousing or noise insulation might be necessary.
- For developments not requiring EIA, yet still necessitating advice on potential impacts.
- For applications seeking prior consent for construction site work, which is beneficial for all involved parties. These applications detail the work, methods, and steps to mitigate noise, using noise prediction software like CadnaA or SoundPlan to calculate exposure based on the software’s inputs. Obtaining consent shields contractors from stop or enforcement notices and can set noise thresholds.
Although standards can specify fixed limits, they are rarely applied today as they do not account for the specific site location and existing noise levels. An older, simpler method provides the following basic guidance:
Between 7am and 7pm, the noise levels outside the nearest window of the occupied room closest to the site boundary should be:
- 70 dBA in areas away from main roads and heavy industry
- 75 dBA in areas close to main roads and heavy industry
The ABC method
The ABC method is widely used and considers ambient conditions when establishing noise thresholds. It requires the measurement of background or ambient noise before construction begins to determine the impact of the work. All measurements must be taken in dBA LAeq, which is the A-weighted equivalent continuous sound level adjusted for human hearing, using a noise monitor or Sound Level Meter.
The measurements should be extensive, typically from 8 AM to 6 PM Monday through Friday, and 8 AM to 1 PM on Saturdays, to accurately reflect the noise during working hours. If possible, measurements should span multiple periods and several days.
Figure 2: Example threshold of significant effect at dwelling
To proceed with the process, round your LAeq dBA measurements to the nearest 5dB. Depending on your rounded value:
- If it is less than the levels in category A, then use category A as your thresholds.
- If it is the same as the values in Category A, then use Category B thresholds.
- If it is more than the levels in category A, then use category C thresholds.
- If it is higher than the values in the table, refer to NOTE 2.
Figure 3: Calculation example
5dB(A) Change Method
This method stipulates that noise limits from construction activities are considered significant if:
- The construction noise (including ambient noise) exceeds the pre-construction ambient noise levels by 5dB or more.
- There are lower threshold values of 65dB for daytime, 55dB for evening, and 45dB for nighttime. Threshold values should not be set lower than these specified limits.
Placement of Noise Monitors and Threshold Adjustments
Due to practical constraints like power availability and theft prevention, it is not always feasible to install noise monitors at the closest residence. Therefore, monitors are often positioned at the site’s perimeter. In such cases, it may be necessary to modify the threshold levels of the monitors to account for their distance from the nearest dwelling.
Figures 3 and 4 provide standard distance corrections. A doubling of the distance from the noise source to the receptor requires a 6dB correction, as illustrated in the diagrams below. Alternatively, noise prediction software such as CadnaA or SoundPlan can be used for more precise adjustments.
Figure 3: Distance adjustment K’ for plant sound power method
Figure 4: Example to illustrate a standard calculation.
Sonitus Systems offers both the hardware and software for a range of environmental parameters on a continual basis, with real-time information available through our Sonitus Cloud dashboard. For more details on our indoor and outdoor noise and air quality monitoring products and services, please contact the team at https://www.sonitussystems.com/contact-us