It’s hot outside, so can I open the windows? Well, that depends on how noisy it is outside at night.
In December 2021, Approved Document O – Overheating (ADO) was published.
Regarding noise, ADO states:
“Windows are likely to be closed during sleeping hours if noise within bedrooms exceeds the following limits.
a. 40 dB LAeq,T, averaged over 8 hours (between 11pm and 7am).
b. 55 dB LAFmax, more than 10 times a night (between 11pm and 7am).”
For reference, the above levels appear to be the 30 dB LAeq,8hr from BS 8233:2014 Guidance on sound insulation and noise reduction for buildings and the 45 dB LAFmax from World Health Organisation (WHO) guidance in bedrooms at night with a 10 dB relaxation on each.
Based on a partially open window providing an outside-to-inside level difference of 13 dB (reference Association of Noise Consultants’ Acoustics, Ventilation and Overheating Residential Design Guide – AVO Guide), this means that where external noise levels at night exceed either 53 dB LAeq,8hr and/or 68 dB LAFmax, an alternative cooling strategy must be adopted.
This will limit the use of windows as an overheating mitigation strategy in many urban areas.
Well before automatically turning to comfort cooling (air conditioning) which is arguably a non-sustainable approach, there are a few acoustic tricks up our sleeves. Incorporating open windows with a sound attenuating balcony could provide a noise reduction of around 20 dB. Similarly, the use of attenuated vents/louvres has the potential to provide a noise reduction of around 23 dB. By utilising both attenuated vents/louvres AND sound attenuating balconies, a noise reduction of around 30 dB is possible.
A couple of other things to note are that the ADO criteria only relate to night-time in bedrooms (i.e., no criteria for daytime noise levels during overheating mitigation) and that the criteria do not align with guidance from the AVO Guide.
Given the challenges involved in mitigating overheating while maintaining appropriate internal noise levels, early involvement with acoustic consultants is key. Our noise and vibration team here at Temple already work on several residential schemes where we’re helping to resolve these issues so feel free to get in touch if you would like us to help with yours.