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!