Poor air quality is known to significantly affect human health, and comfort. While outdoor air quality often receives greater attention due to public awareness and legislation, the interaction between outdoor and indoor air quality is important and often overlooked. Understanding this relationship is the first step in creating healthier living and working environments, particularly as we spend around 80% of our lives indoors.

How does outdoor air influence indoor air quality?

Opening windows to let ‘fresh’ air into a space is a natural response to feeling that a room is stuffy, especially if there are unpleasant odours indoors and the air outside is perceived to be clean. Whilst, across much of the UK, opening doors or windows to ventilate indoor air is relatively safe, outdoor air could be more contaminated, particularly in busy urban environments. This is particularly likely if windows are opened at ground floor level, close to heavily trafficked or congested roads, or effuse points from industrial processes.

The age-old issue with raising awareness of air pollution is that we can’t see it and often, we also can’t smell it. Therefore, opening windows to ‘purify’ indoor air can simply be an illusion. As such, in highly polluted locations, such as Air Quality Management Areas (AQMAs), windows may be best left permanently shut and mechanical ventilation systems are used to actively remove contaminants.

Nevertheless, outdoor pollutants can still find their way indoors, especially in older, poorly sealed buildings. Fine particulate matter (PM_2.5), nitrogen dioxide (NO₂), and ozone (O₃) to name a few, can pass through gaps in façades and contribute to poor indoor air. These effects may be particularly prevalent in built up urban areas with ‘street canyons’, with busy roads between tall buildings. This creates a barrier that shields pollutants from the wind or leads to their recirculation, thus reducing their dispersion.

How do indoor pollution sources contribute to the problem?

There are countless household products which contribute to the worsening of indoor air quality, however due to a lack of research and public awareness in comparison to outdoor sources, and the usefulness of these chemicals in our everyday life; little action has been taken to educate the public on the known health effects or to restrict their use within the home.

Volatile organic compounds (VOCs) are released from common household sources such as cleaning and personal care products, air fresheners and candles, flooring, paints and upholstery, and can – often unknowingly – disrupt focus and cause discomfort, headaches, and respiratory conditions.

Also significant is particulate matter (PM₁₀, PM_2.5) which is released from cooking and combustion processes. A new study found that pollutants from gas stoves kill around 40,000 Europeans each year, twice as many as killed from car crashes. Interestingly, air frying was found to be the least polluting cooking method (adding to the long list of reasons you should get one!).

How can we tackle it?

Tackling indoor air quality is a complex issue, however a good starting point is to understand the interaction between indoor and outdoor air pollution as much as possible, to isolate any issues. Below are some measures that could be factored into the building design:

• Ventilation Control: Using high-efficiency particulate air (HEPA) filters in heating, ventilation, and air conditioning (HVAC) systems can ventilate rooms without the need for openable windows that may compromise air quality.
• Sealing and Insulation: sealing windows, doors, and other openings properly can limit the unintentional entry of outdoor pollutants, especially in high-traffic or industrial areas. However, awareness of the potential to trap indoor pollutants is vital.
• Accreditation: there are many guidance documents which set standards for indoor air quality, such as the WELL Building Standard and BREEAM. Gaining the Hea 02 Indoor Air Quality BREEAM credits is ensures that indoor air quality has been considered throughout the design, build and fit-out and that future building occupants can enjoy a safe and healthy indoor air environment.

https://www.theguardian.com/environment/2024/oct/28/pollutants-from-gas-stoves-kill-40000-europeans-each-year-report-finds#:~:text=Gas%20stoves%20kill%2040%2C000%20Europeans%20each%20year% 20by%20pumping%20pollutants,public%20awareness%20of%20their%20dangers

https://www.birmingham.ac.uk/news/2024/air-fryers-confirmed-as-least-polluting-cooking-method

• Health Concerns and Policy Implications – Air quality continues to be “the largest environmental risk to public health in the UK”. The COVID-19 pandemic has also raised questions about the link between poor air quality and COVID-19 outcomes (and therefore wider health impacts).

• Governance and Enforcement – Following Brexit, environmental law, regulations and policy are no longer subject to EU oversight. This change may lead to shifts in how air quality regulations are monitored and enforced, potentially affecting developers and planners in terms of compliance requirements and enforcement mechanisms.

• Changes to EU Air Quality Standards and Objectives – The European Commission intends to revise the Ambient Air Quality Directive to align air quality standards with World Health Organization (WHO) recommendations, which are much tougher. It is likely that the UK will follow, and we have already seen some Councils, such as London Borough of Camden, adopt stricter limits. As such, the constraint posed by air quality is likely to vary significantly from borough to borough.

• EU Infringement Proceedings and Judicial Reviews – The UK has faced EU infringement proceedings and private judicial reviews related to its failure to meet air quality targets. These legal challenges have resulted in the government being required to produce air quality plans aimed at reducing pollutant levels. Fines may still be imposed – although it’s not clear legally whether the UK could be forced to pay, following Brexit.

The full report is available here: https://researchbriefings.files.parliament.uk/documents/CBP-9600/CBP-9600.pdf

What is Part O?

Over the past year, Part O has steadily made its presence felt in the planning and design stages of residential projects. Most residential designers and developers will now have some experience of it.

Part O was introduced to the Building Regulations to address the increasing problem of overheating in new residential properties. The problem has escalated over the last couple of decades as buildings have become increasingly insulated, more airtight, and equipped with lightweight facades featuring expansive glazing. Simultaneously, rising global temperatures have exacerbated external heat levels. (We have all probably had some experience of trying to relax or sleep in an overheated room – it’s not pleasant!)

Part O contains specific design requirements for the control of overheating that now must be complied with. There are two routes to compliance, a simplified method and a detailed method. We provided a webinar discussing the criteria in detail at the time when Part O was introduced. If you are interested, the relevant section of the webinar can be seen here.

Noise requirements

Regardless of whether compliance is sought via the simple or detailed method, Part O contains a separate noise-related requirement that if noise levels will exceed defined levels in bedrooms at night with their windows open, then the dwellings must be designed so that they will pass the overheating assessment with the bedroom windows closed.

The aim of this requirement is to help avoid the situation where residents are forced to open windows and expose themselves to high noise levels that may disrupt sleep quality – a crucial consideration for health and well-being. (We’ve all probably experienced the detrimental effects of noise on a good night’s sleep!)

The noise limits in Part O are very low, and therefore we have seen that for most new developments, even those in areas we would considered to be relatively quiet, there have been restrictions on the opening of bedroom windows for the overheating assessment.

In nearly all cases where bedroom windows have needed to be kept closed, the bedrooms have failed the overheating assessment initially and additional mitigation has been necessary.

It’s worth noting that ongoing industry discussions are advocating for the relaxation of the stringent noise limits in Part O due to the absence of sufficient technical evidence supporting their current severity. Stay tuned to our LinkedIn page for updates on this front.

Solutions

The ideal solution for Part O compliance is to design residential developments so that all bedrooms have access to a window on a quiet facade. Occupants will then be able to keep the windows open without compromising internal noise levels.

However, this is often not possible due to site locations and other design considerations/limitations, particularly the need to optimise the value of the site and therefore achieve a good density of dwellings. The layout of the development is also normally already fixed by a planning consent and therefore there is little to no flexibility in the development layout.

Furthermore, as above, the noise criteria in Part O are also very low and therefore we regularly see exceedances on sites that would otherwise be thought of as relatively quiet.

In these cases, modifications must normally be made to the design of the development to reduce overheating. From the projects we have worked on since Part O’s introduction (roughly 40 separate developments), the following additional mitigation have been chosen for affected dwellings/bedrooms to achieve compliance (from most common to least common):

• Low g value glazing (including triple glazing)
• Enhanced mechanical ventilation (either MVHR systems, or in some cases purge fans to affected rooms)
• Tempered air (normally a cooling unit attached to an MVHR system)
• Full comfort cooling (i.e. air conditioning)

Blinds are known to be effective at helping to mitigate overheating however only integral blinds (i.e. those where the blind is within the glazing) are officially allowed for Part O compliance. These are expensive and generally considered to be undesirable due to maintenance, cleaning etc.

Solar shading is an excellent solution to overheating however needs to be factored into the design of buildings early on and prior to the planning application. We anticipate a growing use of solar shading in development design over the next 5-10 years as shading products improve, and architects and developers increasingly recognize their broader benefits.

It is also worth saying that we have seen a large variation in attitudes from Building Control Officers in relation to the need to achieve full compliance with Part O. Some officers have taken a more pragmatic view on achieving full compliance given some of the practical difficulties and conflicts with other building regulations requirements (e.g. security, max. window openings, etc). As with all new and complicated regulations, individual officers’ understanding of the requirements can also vary.

How to avoid issues on your projects

 Given the cost and design implications of the mitigation measures listed above, we would always recommend that developers and design teams start thinking about Part O compliance at the earliest stages of design (i.e. RIBA Stages 1 & 2). This will ensure that any necessary mitigation is minimised and/or costed into the project as appropriate. It will also allow measures such as solar shading to be considered.

Having worked on a number of projects to date (and being very familiar with noise affecting developments generally) we are more that happy to give initial advice on where Part O noise limits are likely to be exceeded and provide free outline advice on possible solutions. Please do get in touch if you have a project you would like us to look at for you.

We would also recommend early consultation with Building Control to establish their views.

Summary

• Part O compliance has significantly impacted the design of new residential developments, particularly those situated in urban areas where noise levels are typically higher.
• Addressing compliance early in the design process allows for more accurate budgeting and better optimisation of treatments.
• We are available to provide initial advice on where Part O noise limits are likely to be exceeded and outline guidance on possible solutions for budgeting and design coordination.

We hope you find this article helpful. Should you require more detailed information, we can offer comprehensive CPDs on Part O. Additionally, remember to follow us on LinkedIn to stay informed about developments in Part O and other matters related to acoustics and air quality.

Two key new Bills with a focus on environmental protection, which will influence our assessment methodologies and planning submissions, are currently passing through parliament.

Part 6 of the Levelling-up and Regeneration Bill introduces Environmental Outcomes Reports (EORs). These are intended to replace EIAs/SEAs in many cases and will require developers to prepare a report on the environmental outcomes of projects of a certain type/scale (to be confirmed in subsequent regulations). The EOR would need to be submitted to the relevant local authority and made available to the public.

The intention is for statutory environmental assessment to follow a clearer path, with:

• Clear criteria for what aspects of which disciplines need assessing
• Proportionate assessment against agreed outcomes
• Greater clarity on mitigation requirements and alternative schemes that should be considered
• Succinct, non-technical reporting that is accessible to all stakeholders, including decision makers and communities
• Stronger enforcement of mitigation, with post-construction monitoring and reporting to support understanding of the long term environmental impact.

Alongside this, the Clear Air (Human Rights) Bill seeks to enshrine that the right to breathe clean in UK law. The Bill aims to reduce air pollution by introducing measures such as low-emission zones and promoting active travel. It also includes provisions to improve air quality monitoring and to increase public awareness of the health impacts of air pollution. This is likely to lead to great scrutiny of planning applications, with respect to air quality.

In summary these Bills, which have cross party support, are set to have a significant impact on planning applications, with greater clarity on (and likely tougher) assessment criteria, mitigation requirements, and an increased emphasis on post-construction monitoring.

Sections 60 and 61 of the Control of Pollution Act 1974 (the Act) deal with the control of noise and ‘prior consent for work’ on construction sites.

What is a Section 60 Notice?

The local authority may impose noise control requirements (typically via conditions attached to a planning consent) on a person or company (the Contractor) when they carry out engineering works.  The notice may specify:

• Working practices (e.g. methodology or equipment);
• Working hours;
• Noise limits for the site, possibly including specified hours.

The Act requires that in serving notices the local authority should have regard to:

• Ensuring that “best practicable means” are employed by the Contractor to minimise noise;
• Making the Contractor aware of other methods or plant or machinery that the local authority considers more acceptable; and
• Protecting any ‘sensitive receptors’ near the site from the effects of noise.

Construction noise monitoring at Ocean Village, Southampton for Bouygues

What’s the Problem with a Section 60 Notice?

A Section 60 notice may be served by the local authority at any time without consultation with the Contractor or developer. Furthermore, the requirement under a Section 60 notice can be made more onerous if the local authority receives and upholds complaint in the vicinity. This can have significant implications for the programming and costs of the works.

Failure to comply with a Section 60 notice is an offence without “reasonable excuse” and can lead to prosecution in a Magistrates Court.

What’s the Alternative?

The Contractor may apply to the local authority to start work under a Section 61 Agreement.  The Agreement must be completed prior to the start of construction work and requires the Contractor (typically in conjunction with their acoustics consultants) to provide detailed information on:

• The works and the method by which they are to be carried out; and
• Measures to minimise noise resulting from the works.

If the local authority approves the Section 61 application then legally they cannot serve the Contractor with any Section 60 notices throughout the construction programme, provided that the Agreement is adhered to.  This protection can be an attractive approach for sites where noise or vibration is likely to be an issue.

In our experience Section 61 Agreements can take some time to negotiate, especially for complex construction sites.  However, once an application has been submitted, the local authority must inform the applicant of its decision within 28 days.

Monitoring Noise & Vibration at Creekside, Greenwich for Essential Living

How Can We Help?

• We can accurately and cost-effectively calculate noise emissions;
• We can advise the Contractor or design team on appropriate noise reduction measures having regard to programming and cost implications;
• We can assist the Contractor in negotiating and securing suitable Section 61 agreements;
• We can provide assistance with temporary or permanent noise, vibration and dust monitoring to comply with any obligations imposed under Section 60 or 61 of the Act, or in the event of complaints.

The term decibel or ‘dB’ is often used in the development and construction industries but very few people know what, for example, a 1dB noise reduction sounds like, or whether it is worth achieving. This can lead to unnecessary argument over what can be negligible improvements.

This short film shows the effect of different reductions in noise levels (in this case 1dB, 3dB, 5dB and 10dB) comparing the starting ‘reference’ noise level with a given noise reduction. It replays the same short film clip over and over so a direct comparison between the different levels is possible.

Food for thought perhaps when someone insists that you achieve that last 1dB of a contractual requirement!

Cass Allen has worked on the acoustic design of many large-scale mixed-use developments containing gyms. The gyms have ranged from small single-room gyms for residents only through to larger independent commercial gyms (Fitness First etc). Here are five key acoustic considerations when designing gyms in mixed-use developments:

1. The location of the gym in the development

Gyms can generate high levels of airborne and impact noise and so they should ideally be located away from residential units. However, this is not often possible and gyms are increasingly being located in mixed-use developments adjacent to habitable areas. In these cases high acoustic performance separating wall and floor constructions will normally be required to ensure that neighbouring residents are adequately protected.

2. The type and size of gym

Some gyms will generate more noise than others. This depends on the size of the gym but also the type of activities and equipment used in the gym. The following activities/areas generally dictate the type and levels of noise generated:

• Group fitness classes – high music noise levels and potentially high levels of impact noise from people exercising in unison, etc.
• Free-weights areas – high impulsive noise from free-weights impacting on the floor.
• Machine-weights areas – can generate high noise levels from weights impacting on each other and the machine body.
• Cardio-machine areas – bikes, rowing machines etc. These machines tend to be quiet compared with other noise sources.

In medium to large gyms, music tends to be played at high noise levels and often dictates the overall average noise levels with impacts from free-weights dictating maximum impact noise levels.

Cass Allen has carried out a number of noise surveys in gyms of different sizes and types in order to quantify noise levels from different activities and equipment.

3. Appropriate acoustic design targets

To minimise the risk of complaints regarding gym noise, we recommend that new mixed-use developments are designed so that noise from the gym is generally inaudible in adjoining dwellings. This will require a much higher level of sound insulation than the minimum requirements in Part E of the Building Regulations.

Inaudibility is difficult to quantify as it is dependent on the background noise levels at the receptor position, which cannot be accurately predicted if the development is not yet built. In these cases it is necessary to adopt nominal design targets. The following internal noise targets are normally recommended:

• Design targets for maximum gym noise levels in habitable rooms of adjoining residential properties:
  • Daytime (0700-2300hrs) – 20 dB LAmax
  • Night-time (2300-0700hrs) – 10 dB LAmax

If the development site is particularly quiet it may be necessary to reduce these noise targets.

4. Control of impact sound transmission

Free-weights areas and gym classes can generate high levels of impact noise, which, if unmitigated, is likely to travel effectively through the building structure and disturb adjoining residents. Impact noise from gyms is difficult to quantify and predict and therefore a ‘best practice’ approach is generally proposed whereby the following anti-vibration treatments are included within the gym design:

• Cardio machines, weights machines – Machines placed on resilient floor matting
• Free-weights areas – Resilient floor systems (sprung floor or bespoke resilient floor build-up incorporating mass layer)
• Group gym class areas – Specialist sprung floor systems

Even with the treatments listed above, it may be necessary to impose management restrictions regarding, for example, the hours that the gym can be used, and it is still recommended that gyms are not located directly above residential units wherever possible.

5. Reverberation control

Reverberation treatments should also be considered for medium and large-scale gyms to provide good quality acoustic environments within the gyms themselves. This is particularly important for group class areas where speech intelligibility between the teacher and class members is important. Generally, good internal noise environments can be achieved using acoustic absorptive ceiling or hanging absorbers.

If you would like further information on the acoustic design of gyms in mixed-use developments please call us on 01234 834 862.

We are experienced in the planning, design and testing of large developments for major developers (e.g. Barratt Homes, Berkeley Group, Bouygues, Bellway Homes, Morgan Sindall, Hill Partnerships, Midgard, Kier Group, Mulalley, Mace Group, Taylor Wimpey, Telford Homes, United Living (South) Ltd).

As part of the acoustic design reviews we carry out we always look for value engineering opportunities. We can often save our clients a significant amount of money by ensuring that materials are only specified where required.

Please see below 10 common value engineering opportunities in the design of new residential developments:

1) Acoustic resilient layers in addition to EPS insulation in concrete floors:
Where floors are constructed from precast or in situ concrete slabs, an EPS thermal layer under a floating screed will normally provide the required impact sound insulation. A dedicated acoustic resilient layer is therefore not normally required.
2) Extra acoustic insulation in walls or floors:
As a general rule, it is not worth adding more than 25mm of mineral wool into a wall or floor cavity that is smaller than 100mm and more than 50mm of mineral wool in a cavity that is more than 100mm. The additional benefit of thicker insulation is marginal and therefore generally not cost affective.
3) Acoustic insulation in internal walls:
Insulation is not necessary within internal walls within dwellings provided that you have room to use a 70mm stud. The following wall construction is compliant with Building Regulations Part E requirements and is often much easier/quicker/cheaper to install onsite that a thinner wall containing acoustic insulation: 12.5mm high density plasterboard (min. surface mass 10.6kg/m2) either side of a 70mm metal C-stud.
4) Reverberation control in common areas:
Building Regulations Part E requires that reverberation control is provided in communal areas (corridors etc). However, reverberation control is only strictly required in communal areas that provide <strongdirect access to dwellings. Communal areas that do not contain apartment front doors do not need to be treated. This generally means that reverberation control is not required in entrance lobbies or stairwells.</strong
5) Attenuators in MVHR systems:
Attenuators are often over-specified in MVHR or MEV systems. As a general rule it is not necessary to include attenuators in ducting between MEV/MVHR units and external supply inlets and discharge outlets. If attenuators are required between the MEV/MVHR units and habitable rooms it may be more cost effective to upgrade the MEV/MVHR units to quieter models (see below) rather than use the attenuators. Some attenuators also only offer poor sound attenuation and therefore are not cost effective.
6) Acoustic resilient layers in hotels or student accommodation:
Carpet can be used to control impact sound within hotels or student accommodation because the building operators will have control of floor finishes. Therefore, a dedicated acoustic resilient layer may not be required.
7) ‘Acoustic’ products:
We sometimes come across ‘acoustic’ products that claim to have special ‘acoustic’ properties. Often the benefit of these materials is marginal at best. Sometimes the claims are simply wrong. If in doubt contact Cass Allen for an impartial view.

So what do you do with all those cost savings? Well, there are some areas where we generally recommend spending that little bit extra. The following items are normally recommended to improve the development and may save money in the long-term by preventing noise-related complaints from future occupants:

8) Independent wall liners to lift shafts, stairwells and bin stores:
Lifts tend to be well isolated these days however complaints regarding structure-borne lift noise do sometimes occur. We therefore generally recommend installing independent wall liners to any walls separating habitable rooms from lift shafts. Independent wall liners minimise the likelihood of complaints and subsequent expensive investigations and remedial works. We also recommend independent wall liners to bin stores and stairwells where regular impacts on the separating walls may also occur.
9) Over-sized MVHR units:
Noise levels generated by MVHR units can vary considerably when moving the same quantity of air. A smaller MVHR unit will have to spin faster and work harder than a larger unit and this leads to more turbulence and higher levels of noise. A doubling of fan speed results in a ~16 dBA increase in noise. It is therefore often worth spending a bit of extra money on larger MVHR units that can comfortably achieve required airflow rates. This is particularly cost effective if it means that attenuators or acoustic duct lagging are not required or if it prevent future complaints from residents.
10) Anti-vibration mounts for pipework in plant rooms:
Pipework in plant rooms is often hung directly from the slab above. Structure-borne noise from the pipework can be audible in the rooms above and consequently provoke complaints from affected residents. Where residents are located above plant rooms, we recommend installing the pipework on anti-vibration mounts/hangers to minimise the likelihood of complaints and/or subsequent expensive investigations and remedial works.

We hope you find the above examples useful. Please get in touch if you would like to discuss any of the above examples or if you would like us to review any of your projects in more detail.

Whenever a new development is built, it impacts the way in which wind moves through an area. This is not a consideration that you may immediately associate with acousticians, however, in tall buildings with certain types of façade elements, it can be a real acoustic problem.

Wind flow across any building will generate noise – this is due to turbulent airflow around the edges of the building. At higher wind speeds this is generally audible as a broadband or slightly tonal ‘wooshing’ sound. People are generally familiar and accustomed to this noise and therefore it is rarely considered to be a problem.

However, under certain conditions, wind can cause building elements to vibrate which can potentially generate high noise levels.

It is quite rare for this to be a problem, however, when it is, it can be quite dramatic.

The weird ‘alien like’ sound that can be heard in the video is caused by the vibration of the ‘blades’ on the roof of the building. This vibration occurs at certain wind speeds and directions.

Smaller façade elements tend to be most susceptible to tonal wind induced noise, such as architectural baguettes, solar shades, cables, small apertures etc. This is because the natural resonant frequency of these objects are more likely to be in the audible frequency range (20-20,000Hz).

There are general guidelines that can be followed to minimise the risk of vortex shedding problems in the design of new buildings:

• Any circular façade elements with a diameter of less than 50mm should be avoided where possible.
• Where small façade elements are required, ensure the façade elements are sufficiently damped and consider modifying the design of the façade elements to break up vortices (this can be achieved by adding fins or other design features designed to break up vortices).
• If repeated façade elements form part of the development design, they should be spaced irregularly to avoid periodic vortices becoming established.

Testing and modelling can also be carried out to further assess whether any issues are likely to occur including:

a) Modelling the façade elements using Computational Fluid Dynamic (CFD) software or;

b) Conducting tests of the façade elements in a wind tunnel.

If you would like guidance relating to tonal wind induced noise or any other acoustic aspect of your project, please contact us and we would be happy to assist.

If you’ve found this article interesting, have a look at these other examples of vortex shedding occurring in various contexts; some of them are quite dramatic!

The fall of the Tacoma Bridge

Cloud formations around madeira

Lamp posts dancing on the M62

Aeolian Harp – an instrument that sings in the wind as a result of vortex shedding