As acousticians we regularly work with housebuilders, typically advising on them on matters of acoustic design relating to sound insulation and the control of external noise.  My practice, 24 Acoustics, is no different and we can list the majority of blue chip nationwide housebuilders as our clients.

The construction of housing either on brownfield sites or on the edge of towns means that the impact of environmental noise is often a significant consideration as part of their planning process.  Any residential development within earshot of a road or railway in particular (but also any other source of environmental noise) is likely to require a noise impact assessment to support the planning application.

Our role really should be to get involved at a very early stage and assess the impacts before the architects have sharpened their pencils.  Pleasingly some developers do exactly this and when given this opportunity we are able to mitigate external noise impacts through effective masterplanning and property orientation (internal and external). 

Often, however, we’re brought on board later and have to mitigate noise within an already largely defined layout.  What is left might then be considered a ‘residual impact’ and the last resort is to consider noise impact internally in dwellings with windows closed.  Depending on the site, it is not uncommon to have to specify windows systems with enhanced sound insulation characteristics in order to keep the sound at bay (this can comprise glazing with a variety of thicknesses, differing airgaps and acoustically laminated glass too). 

Clearly the issue with this is that if residents need to occupy their new homes with windows closed then in order to do so consideration must be given to alternative means of ventilation in accordance with Approved Document F of the Building Regulations (Ventilation) which defines requirements for both background and purge ventilation. 

Background ventilation is the provision of the air that we breathe day in, day out and (on non-noisy sites) is generally provided by the trickle vents that you’ll see in the head of a window.  For noisy sites acoustically-rated vents are available which can range from an attenuated vent in the window to a ducted vent through the wall (potentially with a built in fan) to full ducted mechanical ventilation and heat recovery systems (MVHR). 

Purge ventilation is defined as that necessary for the dispersal of odours and vapour.  Traditionally it’s provided by throwing open a window.  Of course, the disadvantage of this is that by opening the window you compromise the sound insulation that the building façade has been designed to provide and have to balance the resulting noise impact with the desire for fresh air (which may not in fact be that fresh if the noise source that you are attempting to mitigate is a road!).  It has generally been assumed (rightly or wrongly) that this would occur for only short periods of time and once the odour or vapour has dispersed the resident would be happy closing their window and enjoying the associated relative peace.  

There is, however, another factor at play and it is that of overheating.  Clearly any resident that needs to keep windows closed as a means of mitigation of external noise may be at risk of excess thermal gain in their dwelling. 

This has been conveniently ignored by us all for as long as I can remember.  Until now.  Approved Document O of the Building Regulations (Overheating) came into force in June 2022.  It did not apply to work subject to a building notice, full plans application or initial notice submitted before that date provided the work commenced before 15 June 2023.. hence is only now just starting to bite.

It’s obvious when you think about it.  In particular, southerly aspect dwellings with large glazed areas to habitable rooms and a requirement to keep windows closed or otherwise put up with unacceptably high levels of external noise, gives those unfortunate residents a trial-by-ordeal style choice of unsatisfactory living conditions.

Part O requires developers to design their new dwellings to minimise the risk of overheating and takes into account the situations in which it is necessary for residents to rely on closed windows as a means of noise mitigation.  Secondary design measures can include consideration of shading, glazed area, mechanical ventilation and, as a worst-case provision of cooling systems.

There is absolutely no substitute, however, for good acoustic design undertaken upfront at the conceptual stage which in some cases would avoid the need for the secondary measures described above.  A lot can be achieved with appropriate masterplanning and internal layout and we would encourage developers and their design teams to engage with us at an early stage to achieve sustainably designed dwellings in which people will enjoying living.

Reuben Peckham.