Approved Document O – Noise Implications across the UK

Approved Document O

The criteria for noise control under overheating conditions was previously based on the Acoustic, Ventilation and Overheating (AVO) guidance by the IOA and ANC. However, although informative, this document did not provide clear cut noise limits, requiring consultants and local authorities to use their professional judgement.

Approved Document O (ADO) was adopted in England on 16th June 2022. The approved document is largely centered around overheating, however it includes a number of statements which impact upon the design of noise mitigation. Prior to ADO, overheating and noise control had been applied sporadically and inconsistently, with differing advice from noise and overheating consultants. The release of ADO is therefore a milestone in providing a consistent approach in addressing overheating and noise control.

The Welsh Government will be adopting Approved Document O from the 23rd of November 2022. The Scottish Government will be considering overheating from the 1st of December 2022 and have amended their technical handbooks which explain how to achieve the requirements set out in the Building (Scotland) Regulations 2004.

What is clear is that the requirements of the building regulations in the different nations are not the same.

Approved Document O will have a significant impact on schemes going forward. How this is implemented both at planning and design stage will require careful thought.

All three nations require the building work to meet all relevant requirements of the Building Regulations and that the overheating mitigation strategy is “usable”. The English and Welsh versions state:

“Requirement O1(2)(a) is met in a new residential building if the building’s overheating mitigation strategy for use by occupants takes account of all of the following. 

1. Noise at night”.

ADO (England) 

ADO (England) goes on to state:

“3.2 In locations where external noise may be an issue (for example, where the local planning authority considered external noise to be an issue at the planning stage), the overheating mitigation strategy should take account of the likelihood that windows will be closed during sleeping hours (11pm to 7am). 

3.3 Windows are likely to be closed during sleeping hours if noise within bedrooms exceeds the following limits. 

1. 40dB L_Aeq,T, averaged over 8 hours (between 11pm and 7am).
2. 55dB L_AFmax, more than 10 times a night (between 11pm and 7am).”

The limits applied in 3.3 above are indoor noise levels at night. These limits could be interpreted as what building regulations consider reasonable indoor noise levels under overheating conditions.

The important point to note is that these limits are 10dB greater than those applied under normal conditions and with background ventilation in use. Secondly, it is a clear criterion that can be worked to by acousticians and local authorities (building control and environmental health) when providing noise control advice and determining applications.

ADO (Wales)

ADO (Wales) states:

2.2 High levels of external noise could limit the use of cross-ventilation to mitigate the risk of summer overheating. External noise is a material consideration considered when applying for Planning permission and mitigating measures may be required in the design in order to obtain Planning permission and controlled through a condition imposed on the consent. In exceptional cases, this could include non-openable windows. More commonly, windows will be openable in order to enable natural ventilation to occur at less sensitive times of day, when there is lower noise, when people are not present in the room, or when they are present but not engaged in noise-sensitive activities. But those windows may need to be kept closed at times to maintain acceptable indoor acoustic conditions, for example when people are using the rooms for sleep or office work. A noise issue may be identified at the Planning stage but rely on occupants to close windows at noise sensitive times rather than prevent them from ever opening them, and in those cases overheating strategies should assume windows will be closed during noise-sensitive periods even if they are not fixed closed.

2.3 When the removing excess heat as part of the overheating strategy, noise levels in bedrooms should be kept to a minimum during the sleeping hours of 23:00-07:00. Building control bodies may accept as evidence that this requirement is satisfied: 

1. documentation to demonstrate that the local planning authority did not consider external noise to be an issue at the site at the planning stage or; 

23. if the local planning authority did consider external noise to be an issue that should be controlled through a condition at planning stage, then documentation to demonstrate that the proposals for heat removal (during the sleeping hours of 23.00 – 07.00) are accommodated within or do not conflict with documentation provided to the local planning authority to satisfy any related planning permission condition(s). (For example any expectation that windows on one or more façade, or in certain rooms, will need to be kept closed during noise-sensitive periods.)”

ADO (Wales) does not apply any clearly defined noise limits. ADO (Wales) relies on the noise criteria within planning conditions or documentation submitted at planning stage.

It is important for the noise limits for overheating in Wales to be clearly defined at an early stage. This will require greater input from acousticians, planning consultants and local authorities. This will also require clients adopting and agreeing to overheating control measures at planning stage, rather than developing them through the design stages.

In most cases we would likely be working to the same noise limits applied in ADO (England). However the acceptability of these limits would be largely down to the local authority and some may apply a more or less onerous criteria.

Other risks for developments in Wales could occur when developers accept conditions which follow normal practice (i.e. setting indoor noise level limits based on BS8233 and WHO199)which may have been supported by a noise report which did not consider overheating.  At building control stage, a developer will then need to provide evidence that the overheating control measures comply with the original planning consent. These mitigation measures could be greater (10dB more onerous than England) than if  clearly defined overheating noise limits were agreed at planning stage.

Building Standards (Scotland)

Building Standards (Scotland) states:

3.28.4 Practicality of mitigation measures

“Where measures are implemented to mitigate overheating risk, they should be achievable in use. As is the case for provision of ventilation more generally to a building, measures to address overheating risk should take account of the environment within which the building sits. This is particularly relevant to the use of ventilation to reduce levels of overheating. Issues arising from both noise from the immediate environment and air pollution should be considered. Such matters are usually material considerations in the granting of planning permission for development and any proposed mitigation measures should be compatible with issues already identified at the development (for example location of a façade adjacent to a busy road). 

An assessment and statement on how these matters are considered as part of mitigating any identified overheating risk should be provided as part of the building warrant application. This should reference any relevant conditions set under other permissions and the environmental factors considered in determining the approach to ventilation for cooling. A summary of such information should be included within written information provided to the building occupant.”

As per Wales, Building Standards (Scotland) does not apply any clearly defined noise limits and relies on the noise criteria within planning conditions or documentation submitted at planning stage. Within the Scottish guisance it is not clearly defined whether this applies at night only, or at all times.

This will require greater input from and liaison between acousticians, planning consultants and local authorities and the risk of more onerous mitigation measures are likely if the criteria is not clearly defined.

In summary:

• The criteria for noise limits under overheating conditions was previously based on the Acoustic, Ventilation and Overheating (AVO) guidance by the IOA and ANC. However, although informative, this document did not provide clear cut noise limits, requiring consultants and local authorities to provide their professional judgement.
• ADO (England) has closed that gap, ADO (Wales) and Building Standards Scotland have partly closed the gap.
• ADO (England and Wales) require noise and overheating mitigation at night to be considered only.
• Building Standards Scotland has not clearly defined the time period to be considered.
• ADO (England) has clearly defined noise criteria under building regulations.
• ADO (Wales) and Building Standards Scotland criteria refers to the planning consent.
• Early engagement with acousticians and appropriate criteria needs to be agreed at planning stage in England and Wales.

As part of the changes to noise and overheating we are offering CPD presentations to planners, architects and contractors which will help decision makers and designers incorporate noise and overheating into the design at the correct stage to inform site layout, building design and how to effectively and efficiently balance the needs of noise control and ventilation.

With a team of 15 consultants in Bristol, London, Cardiff and Manchester we are ready for the changes across the UK utilising our wealth of knowledge in both planning assessments and technical noise control.