t’s warm. The windows are open … and now it’s noisy too. Many people have little choice but to let street noises drift into hot rooms. Or do they? There are no easy off-the-peg-solutions. But we can use new guidance to minimise or eliminate potential problems for future development through Good Acoustic Design.
With extreme heat now encircling much of the world – and having just been through the hottest June in UK records – a growing challenge in the built environment is to understand how we can reduce not only the impact of higher temperatures, but also noise nuisance issues during hot weather.
This is a serious concern and one, as I would like to explain, that we are keen to address at Enzygo (www.enzygo.com) as the climate crisis becomes more severe.
Modern dwellings are generally being constructed to higher standards than previously required, with a greater emphasis on energy-efficiency and heat retention in individual properties. During winter, this is a great benefit that reduces heat losses and the need for additional heat sources such as central heating.
‘Hot in the city tonight …’
The flip side – as Billy Idol’s song lyrics suggest – is that in summer months when temperatures in urban areas rise, pushed to extremes by global warming, buildings can often become so warm inside that there is a distinct risk of overheating.
Overheating is bad news. It can lead to adverse health effects, including heat cramps and heatstroke, and exacerbate existing conditions that compromise the body’s ability to regulate its internal temperature, with potentially fatal consequences.
The problem is more acute in city centres where the heat island effect can push the risk of overheating up even higher. Worse still, external factors, including security, air quality and in this instance, noise often limit our options for controlling uncomfortable and dangerous heat levels.
Cooler but noisier
When indoors temperatures rise, the typical approach is to open windows and encourage air to flow through rooms and corridors.
Unfortunately, this leads to a second problem – elevated internal noise levels which mean that outdoor sounds can be heard clearly indoors.
The negative impacts of noise include loss of amenity and sleep disturbance. This is a particular concern in city centres where noise intrusion can be significant during both daytime and night-time.
Clearly, a balance has to be struck between the risk of overheating and acceptable indoor noise levels.
Guidance and standards
Recent guidance on noise impacts during periods of overheating highlights the need for a more connected approach to the design of residential properties which balances the two problems.
To help illustrate this, I want to refer to a number of documents which represent current guidance not only on the risks but also treatment options to ameliorate overheating effects in properties.
The Good Homes Alliance guidance on Overheating in New Homes (https://goodhomes.org.uk/wp-content/uploads/2019/07/GHA-Overheating-in-New-Homes-Tool-and-Guidance.pdf) provides a simple means of assessing the risks of overheating in new residential developments. A beta update was released in 2022 (https://goodhomes.org.uk/news/new-tool-and-guidance-launched-to-tackle-overheating-risk-in-existing-homes-and-retrofit-projects).
This tool considers factors such as site geographical location, arrangement of buildings, and the general nature of the surrounding area. Mitigating factors in the design are also considered. These include the general design of a development, massing of dwellings, and other design factors (https://goodhomes.org.uk/wp-content/uploads/2019/07/GHA-Overheating-in-New-Homes-Tool-and-Guidance-Tool-only.pdf).
A simple scoring assessment follows: – in which the resulting score is used as a guide to a development’s overheating risks. The guide then links this score to further steps that need to be taken, including dynamic thermal modelling of the site, and the inclusion of mitigation measures.
The principal forms of guidance that support assessing noise impacts during overheating periods are documented in the following: –
Acoustics, Ventilation and Overheating Design Guidance document (Jan 2020) – https://www.association-of-noise-consultants.co.uk/wp-content/uploads/2019/12/ANC-AVO-Residential-Design-Guide-January-2020-v1.1-1.pdf
Approved Document O of the Building Regulations 2010 – https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1057374/ADO.pdf
Various other supporting documents have been used in this methodology and there are references to other standards within the guidance.
Good design is the key
The principal means of addressing overheating is good design in both cases.
In its most basic form, good design includes considering overheating risks at an early stage of development by looking at factors – already mentioned above – such as site geographical location, buildings and infrastructure, general development design, plus green spaces and natural shade.
Moving on from this, passive design measures are encouraged to tackle excess heat gain. This might include measures that mitigate unwanted solar gains, such as site layout changes, or external shading in the form of shutters or brise soleil that deflect sunlight.
However, mechanical cooling is always considered as a last resort.
Acoustics, ventilation and overheating design guidance
Guidance published by the Institute of Acoustics (IOA) and the Associated of Noise Consultants (ANC) in the Acoustics, Ventilation and Overheating Design Guidance document (Jan 2020) sets out to reconcile sound insulation with ventilation to create good internal acoustic conditions.
The Acoustics, Ventilation and Overheating Design Guidance (AVO) summarises a number of pertinent standards and guidance documents, including elements of the Building Regulations, planning policy, and appropriate internal noise guideline values.
The guidance document uses this additional information to propose a two-staged approach for assessing overheating – the first defining the risk based on external noise levels, and the second assessing internal noise levels on the basis that windows are open for ventilation.
How does this help?
In all instances, the guidance also assumes that there is a degree of tolerance for higher noise levels during (relatively) short periods of overheating. This assumed tolerance is shown in Figure 3-2 which plots the increased tolerance of noise impacts inversely against the frequency with which events occur.
Incidentally, it is important to note that the AVO only considers noise from transport sources.
Approved Document O
More recently, Approved Document O of the Building Regulations 2010 has been introduced to address overheating; it aims “to protect the health and welfare of occupants of the building by reducing the occurrence of high indoor temperatures.”
The document includes the following limits above which “windows are likely to be closed during sleeping”: –
a. 40dB LAeq, T averaged over 8 hours (between 11pm and 7am).
b. 55dB LAFmax, more than 10 time a night (between 11pm and 7am).
The Approved Document also includes a list of geographic areas which are thought to have a higher overheating risk, such as large parts of London and some areas in central Manchester.
The approach championed by the document is to ensure that the overheating risk is mitigated by the following measures: –
- Limiting unwanted solar gain in summer months; and
- Providing an adequate means of removing excess heat from the indoor environment
The background and theoretical basis of the above are all well and good. However they raise a couple of important further questions: –
1) What are the benefits of assessing overheating risks?
2) How is it assessed?
Aside from the planning and statutory obligations, considering overheating risks at an early stage leads to a better understanding of the potential risks associated with any particular development scheme. This can help to maximise the developable potential and highlight mitigation requirements at an early stage, so helping to inform a more holistic approach to the scheme’s overall design.
An initial baseline noise survey at the site will establish existing noise levels in the surrounding area. This will define noise levels that effect various dwellings across the site and highlight the potential ingress of noise.
Alongside the survey, a risk assessment is needed to identify the site’s potential exposure to overheating risks. This will include factors like the site’s geographical location, arrangement, nature of the immediate vicinity, and other pertinent factors such as whether established trees offer shade.
Both the baseline noise levels and overheating risk assessment can be fed into the development’s design, so highlighting and informing elements like the overall design approach, layout considerations, and other factors such as ventilation strategy.
The resulting additional information can then feed through the design process and, ultimately through good design provide cost benefits that reduce or negate the need for expensive, energy-intensive mechanical plant.
Practical mitigation measures
For a residential development, inherent design measures like the three below may provide an ‘easy win’ when applied to overheating risks: –
– Site layout features – design measures such as the provision of green spaces / land buffers between noise sources and dwellings can provide a double benefit. Firstly, increasing the distance provides extra attenuation; secondly, green infrastructure helps to reduce ambient temperatures. Where space is at a premium – as in city centre locations – providing sound attenuating balconies can also help to reduce noise levels affecting a façade.
– Building design – this can include factors like limiting the façade’s glazed area in proportion to the overheating risk; locating sensitive internal spaces on elevations exposed to lower noise levels, and external measures to limit solar gain, such as brise soleil, shutters or external blinds.
– Ventilation strategy – where open window ventilation is not appropriate because of high external noise levels, alternative passive cooling methods can be used – including attenuated or plenum windows, or attenuated vents / louvres.
Approved Document O states: –
‘It should be demonstrated to the building control body that all practicable passive means of limiting unwanted solar gains and removing excess heat have been used first before adopting mechanical cooling.’
Enzygo noise services (www.enzygo.com/noise/)
I want to include more detail on how Enzygo provides noise and vibration services with technical support for residential, industrial, commercial, energy, minerals and waste projects.
Because we are often called on to link a series of interconnected environmental factors, we frequently bring in related disciplines from other team members to guarantee consistent high-quality solutions through all stages of development.
The web link above outlines our service offer in detail. However, points I would like to underline specifically are that: –
– We help – developers, architects, planners and land agents by assessing noise impacts arising from and acting upon existing and future sensitive receptors. Our work helps to maximise developable areas, identify site constraints and where necessary, advise on mitigation measures.
– We also provide – technical support for planning applications; EIA screening and scoping reports; Environmental Statements; planning/permit condition advice and evidencing; plus noise management plans.
We also have expert skills and experience in: – noise and vibration measurement; 3D noise modelling; detailed acoustic design; and building acoustics.
If you would like more information, or want to discuss any of the issues above in more detail, please feel free to contact me directly.
Mark Harrison, Principal Noise Consultant, Enzygo Ltd