By Jack Harvie-Clark, June 2025
(Please note that blogs express the views of the individual authors and do not necessarily reflect the views of the Institute of Acoustics)
Introduction: an evolution in acoustic design
There has been much debate over whether the proposed updates to BS 8233 are progressive or regressive. This article demonstrates how the proposals represent a natural evolution, taking the core principles of UK noise policy and the Professional Practice Guidance on Planning & Noise (ProPG) and reinforcing them within a new framework based on the latest health evidence. While UK noise policy aims to avoid significant adverse effects on health, we have lacked a clear, evidence-based framework to quantify these effects and apply them in the design process. The scientific evidence to measure and evaluate these effects has advanced considerably since the WHO 1999 Guidelines.
A fundamental challenge in UK acoustic practice has been the historical disconnect between internal and external noise levels. Previous standards have adopted the WHO 1999 internal guideline values without linking them to the corresponding external levels, a practice that has been described as taking them out of context [Ref 1]. ProPG began to bridge this gap: the new proposals for BS 8233 complete that bridge.
The vision of ProPG: Good Acoustic Design means freedom to open windows
When published in 2017, the Professional Practice Guidance on Planning & Noise (ProPG) marked a significant step forward. Its most crucial contribution was introducing the concept of "Good Acoustic Design" - a holistic process prioritising passive measures like site layout and building orientation over a simple reliance on façade insulation to enable “good acoustic conditions” for residents.
The guidance was visionary in its central objective: to achieve desirable internal noise levels while allowing residents to open their windows for ventilation. This ambition inherently shifts the focus to the external sound environment. To meet internal targets with an open window, the noise levels at the building's façade must be controlled.
This vision inherent to the ProPG lacked the scientific foundation to support it. Published in 2017, it preceded the evolution in health evidence by just one year. As the ProPG is set within the guidance of BS 8233: 2014, which prioritises the internal sound level targets from WHO 1999, practitioners must work backwards from internal targets to estimate risk from external sound levels. This shift of focus to the external sound environment was a prescient recognition that has been validated by subsequent health research.
The missing link: the arrival of new health evidence
The evidence that the ProPG needed to underpin its approach arrived just a year after its publication with the WHO 2018 Environmental Noise Guidelines [Ref 2]. This was a landmark update, crystalising the evidence-based link between external sound levels and long-term health outcomes.
For the first time, the WHO published source-specific Exposure-Response Relationships (ERRs) for road, rail, and air traffic. This means we can now quantify the percentage of people likely to be highly annoyed or highly sleep disturbed at specific external noise levels. With the publication of the EAA Environmental Noise Guidelines [Ref 3] in June 2025, we can understand that the greatest health impact is now considered to be premature death rather than annoyance or sleep disturbance per se; these are both significant evolutions from the older, environment-oriented guidelines from 1999 and it frees practice from relying on inferred risk. There is a crucial change of narrative implicit in the evolving science – it is the sound level outside a person’s home that is associated with the health impacts. See [Ref 4] for more information on this important shift in perspective from the noise and health science. See Chapter 3 of [Ref 3] for a description of how the health effects of environmental noise are understood.
This new evidence allows us to be specific. For instance, the ERRs show that at 55 dB Lden for road traffic, ProPG equivalently identifies as a “negligible to low risk” for daytime noise (53 dB LAeq,16 hr) and “low to medium risk” for night time noise (47 dB LAeq, 8 hr). But now we know that at 55 dB Lden, 10% of people are highly annoyed. The same level of annoyance is caused by railway noise at just 52 dB Lden and aircraft noise at 45 dB Lden. With this evidence now available, the question is no longer if we should use it, but how to integrate it into UK design practice.
From aspiration to application: how the proposals realise ProPG's vision
The proposals for BS 8233 take the health evidence and use it to create a practical framework that realises ProPG's vision. They use the (updated) WHO's Exposure Response Relationships (ERRs) to establish "Sound Exposure Categories" (SECs) that act as evidence-based acoustic design drivers. These categories translate percentages of the adversely affected population into design parameters, making health impacts tangible in the same way as energy performance targets, if desired. This isn't about replacing the process of Good Acoustic Design that ProPG champions; it's about providing better tools to make that process more effective and explicit. Just as thermal modelling doesn't constrain architectural creativity but guides it toward chosen energy-orientated outcomes, SECs inform rather than dictate constraints; it is a planning decision on how to apply the SECs in practice. Decisions on site layout, building orientation, and the use of barriers can now be informed by quantified health impacts, and the appropriate planning balance can be determined. There is nothing in this framework that inherently limits housebuilding; it simply reveals the health cost of the decisions that are made, where previously evidence was lacking in this regard.
What internal sound levels?
This evolution does not diminish the importance of internal acoustic conditions - these remain an essential element of acoustic comfort. What changes is the path to achieving them. After using the SECs to establish the health risk, an obvious response is to provide equal mitigation in terms of façade sound insulation where there is equivalent health burden. This is a big change from the current concept of seeking to achieve equivalent internal sound levels regardless of sound source – based on the old environment-orientated guideline levels.
The concept of equivalent façade sound insulation for equivalent health burden – rather than seeking equal decibel levels for different sound sources – is important, because it retains the perspective from the source of the health burden – which is the sound source and level outside the dwelling. The implied internal levels have been included in the draft proposals as an alternative design route, due to popular demand within the acoustics community.
Conclusion: the natural progression of evidence-based practice
The BS 8233 proposals continue the journey that ProPG began. Rather than abandoning ProPG's principles, they provide the scientific foundation that ProPG always needed, representing the consolidation of the ProPG aims. This is not a revolution, but an evolution — the natural progression from principle to evidence-based practice.
- What remains constant: The goal of protecting residents, the need for a good acoustic design process, and the importance of achieving acceptable internal conditions.
- What has evolved: The evidence base informing our decisions, and the transparency of the trade-offs.
Where ProPG provided the vision of Good Acoustic Design, the proposals provide the evidence to realise it. Where ProPG aspired to a holistic assessment, we can now quantify the health implications of design choices. By building on ProPG’s foundations with the best available science, this evolution positions UK acoustic practice at the forefront of evidence-based design, delivering what ProPG always intended: a framework where the health burden of noise is transparently considered in the planning balance for sustainable development.
References
- Use up-to-date Guidelines, B. Fenech & S. Stansfeld, IOA Acoustics Bulletin Jan / Feb 2025
- WHO 2018 Environmental Noise Guidelines for the European Region
- Environmental Noise in Europe - 2025, European Environment Agency
- Response to Clarke / Fiumicelli letter, IOA Acoustics Bulletin Nov / Dec 2024
Additional BS8233 Resources: https://www.ioa.org.uk/bs-8233-resources
