Among the many other things designers and builders of residential homes need to consider, ventilation and overheating are probably towards the top of the list of things the end users will probably notice most (perhaps second only to noisy neighbours!).
It is something that needs to be got right!
In modern homes, background ventilation is usually provided by trickle vents or an MVHR system but as proven by recent heatwaves in the UK, what if this is not enough for the residents to keep cool.
The obvious answer is to open a window – but what happens if by doing that, you allow noise to enter the home, so breaching the criteria of BS 8233, your design targets, planning conditions and ultimately preventing sleep and generating complaints from occupants?
As the importance of a good night’s sleep and protection of amenity becomes more and more of an issue to tenants and homeowners, many local authorities have been raising concerns about this at the planning stage for new residential developments. This can lead to some confusion over appropriate design strategies.
Luckily there is some new guidance presented in Approved Document O [ADO], which your acoustic consultant can consider as part of any noise assessment where glazing and ventilation is of concern.
The ADO guidance presents some noise thresholds, focussing on the nighttime hours, to indicate when opening windows to mitigate overheating is likely to be acceptable and when it is not.
The guidance states the following:
3.3 Windows are likely to be closed during sleeping hours if noise within bedrooms exceeds the following limits.
a. LAeq,T 40 dB, averaged over 8 hours (between 11pm and 7am).
b. LAFmax 55 dB, more than 10 times a night (between 11pm and 7am).
In quieter rural or suburban locations, these levels may well not be exceeded, and your ventilation strategy can allow for openable windows in the event of overheating.
However, in most urban locations, these levels are very likely to be exceeded and alternative means of purge ventilation should be considered in your ventilation strategy.
This new guidance is more robust than that which has typically been applied before, therefore designers must be aware that what has worked before may not be suitable going forward.
Clement Acoustics includes an assessment of overheating in line with ADO as standard in our planning stage External Building Fabric noise exposure assessments and our experienced team can provide advice for your next project to ensure happy (and cool) customers.