Our work this week conducting noise surveys in Bristol, London, and Swindon, for residential, retail, and offices. A variety of acoustic assessments.
Acoustics A to Z
C = Construction Noise and Vibration
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…
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What can we do about Construction Noise and Vibration?
C is a topic which covers probably the most obvious of noise nuisances… construction noise. So, you might be thinking ‘surely there’s not much you can do about construction noise?’.
Unfortunately, you’d be half right, there is no magic trick which will eliminate construction noise. If we live or work near a construction site, we’re going to have to put up with the noise to some extent. But, if the noise is too loud, i.e. where conversation inside the nearest building would be difficult with the windows shut, this might be a ‘significant’ adverse effect, an effect that might be considered to be unacceptable.
In this case, the developer and contractor should be taking actions to mitigate the noise and reduce the impact using ‘Best Practicable Means’, that is, reasonable and practicable measures within technical and financial restraints. So, you’d be half wrong as well, there are some steps that can be taken to reduce noise nuisance from construction works.
So, what measures can be implemented?
There are several. We could control noise at source by fitting silencers to equipment; purchasing quieter alternative plant; and servicing machinery and vehicles regularly. We can use barriers or enclosures around equipment, such as moveable screens; site hoarding; or by taking advantage of existing site structures. We can ensure workers are trained to use equipment correctly and considerately, i.e. turning off vehicles and machinery when not in use rather than leaving to idle; taking advantage of barriers and structures; pointing equipment away from receptors; and dropping rubble from a lesser height.
Local acoustic enclosure/screen – reproduced from BS 5228-1:2009+A1:2014
There are also operational and phasing measures, i.e. using alternative methods of construction (there are several methods of piling for example); avoiding conducting the noisiest activities at unsociable hours; or scheduling these noisier works to occur simultaneously to minimise the total exposure time; conducting some of the preparatory work and maintenance off site; using pre-fabricated constructions; and phasing the works to construct buildings on the perimeter of the site first, such that later construction in the centre of the site benefits from noise screening provided by the new structures on the perimeter.
Even just keeping in regular dialogue with the community can be considered a good noise measure. Informing local residents of when, where and what construction activities are taking place, gives them a chance to prepare and avoids an unwanted surprise. Talking to residents about the noise mitigation initiatives also shows consideration to the community and the environment, which should ultimately help to reduce the number of complaints.
This is a brief list of measures, many more can be found in BS 5228 (a commonly used construction noise and vibration standard), or in code of practice guides produced by many local councils.
Will these measures make enough of a difference?
Unfortunately, even following Best Practicable Means doesn’t always mean that construction noise will be mitigated enough to avoid an unacceptable impact. If the noise is too loud and for too long over a significant period of time, even after all reasonable measures have been taken on the construction site, then further measures might be needed at the affected properties.
In the first instance, the affected properties may be eligible for ‘noise insulation’, that is, the installation of secondary glazing to affected rooms and if necessary, additional ventilation provisions to compensate for the need for windows to remain closed. In extreme cases, the contractor may have to offer temporary re-housing away from the construction site, and occasionally even permanent re-housing may be offered, if it is mutually beneficial to both parties.
Are developers and contractors obligated to mitigate construction noise?
Potentially yes, particularly if constructing in an area which is close to dwellings, places of worship, healthcare buildings or education facilities.
If a local authority receives a series of complaints from noise-sensitive properties, then under the Control of Pollution Act 1974, they have the power to serve a Section 60 notice on the site. This notice can restrict developers and contractors in their working practices (i.e. the equipment used or operational times of certain plant); restrict the general operating hours of the site; and potentially impost a noise level limit which should not be breached. This can all have significant implications on the programming and costs of the works, particularly when a Section 60 notice can be served at any time without warning. Failing to comply with the notice can lead to prosecution at the Magistrates Court, so it would be ill advised to ignore this.
So, can an adverse impact from construction noise be pre-empted and avoided before it happens?
Yes, and really in all cases the developer or contractor should assess the risks early on. In some instances, if the construction site does not have sensitive properties in the nearby vicinity, the developer can be reasonably confident that complaints won’t be received. But if this is not the case and the site may be contentious with regards to noise, then the developer may be best served to apply for a Section 61 consent. The purpose of this is to gain permission prior to the works commencing, which then prevents the local authority from serving a Section 60 notice.
Such a consent is obtained by first conducting a construction noise assessment. With knowledge of the schedule of works, the equipment to be used and the operational hours per day of individual machinery, a set of noise calculations and models can be used to predict the likely levels of noise exposure at nearby properties, and the length of time for which they will be exposed. This is used to assess the risk of significant adverse impact, including whether Best Practicable Means are required, or if noise insulation or rehoming is necessary.
Construction noise modelling – Credit: SLR Consulting
If a risk of adverse impact is identified, then the developer should produce a noise management plan. This sets out the programme of activities; the types of machinery and operational hours; the noise mitigation measures that will be employed; and an example of the complaints management procedure, to be agreed with the local authority. It is then the contractors to ensure that the management plan is followed correctly.
I earlier referred to importance of engaging with local community, and gaining a Section 61 consent demonstrates initiative on the developers part to consider the local residents and environment.
But how do we ensure that noise is being mitigated as per the management plan?
In many cases a noise level threshold will be agreed as part of the management plan, and therefore a programme of noise monitoring may be necessary to check that this threshold is being met.
On high impact sites this monitoring may be continuous throughout the whole construction process, with a sound level meter remaining on site in a fixed position at all times. This can transmit live data which can be accessed by an internet portal, to be reviewed by the consultant as and when, who would then produce regular reports (say every month) which are submitted to the local authority to demonstrate that the works are being mitigated and controlled in a compliant manner. Such a system can also be set up to alert the contractor (via text message or email) when a noise level threshold has been exceeded. The contractor can down tools temporarily, find the offending noise source, hopefully mitigate it, and then carry on working once at a compliant noise level.
Construction noise monitoring – Credit: SLR Consulting
On lower impact sites it may be that shorter periods of monitoring can be conducted to coincide with the noisiest periods of construction. For example, a consultant may visit site for a day or two to monitor during the piling phase. Or, monitoring could be done on an ad-hoc basis, in response to complaints received by the contractor, to determine whether noise level thresholds are actually being exceeded.
What about vibration?
Of course, the title of this article is ‘C = Construction noise and vibration’. I’ve referred thus far only to noise, for brevity’s sake, but much of what has been said above also applies to vibration. Vibration can be an issue in dense urban areas with properties within a few metres of construction activities, in particular from piling work.
There are two main issues from vibration. Firstly, the human perception of vibration, i.e. can a resident physically feel a low of level of vibration on their person which is uncomfortable, or in their house which subsequently radiates noise (particularly if you imagine plates and glasses rattling on a shelf). Secondly and in the most extreme cases, the risk of structural damage from vibration. Thankfully this is not a particularly common occurrence, and even when there is some cosmetic damage, i.e. plasterboard cracking, this doesn’t necessarily mean that there is structural damage. Still…. Probably best to get it checked out!
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 email@example.com, or through our Contact Us page.
An easy and obvious topic to start the A to Z… Acoustics! What is it and how does it affect our day to day lives?