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Attenuated natural ventilation options

With the advent of the guidance in ProPG: Planning and Noise, there is an increased need for sound-attenuated natural ventilation to achieve reasonable internal conditions in dwellings, considering noise, ventilation, and overheating.  The first stage of the acoustic assessment described by ProPG is to apply the principles of good acoustic design; this includes the review of site layouts, building massing, orientation and internal layouts, so that reasonable internal noise levels can be achieved in as many dwellings as possible with open windows providing natural ventilation.  However, if some façades of habitable rooms are exposed to noise levels which could result in unacceptable indoor noise levels with simple open windows, then attenuated natural ventilation is an option to consider.

This page outlines the options that are available to provide natural ventilation with enhanced sound insulation compared with typical opening windows.  Information is drawn from our own experience in developing these designs as well as from others in the Association of Noise Consultants’ group for Acoustics Ventilation and Overheating, our literature search, and our conference papers listed at the bottom of the page.

The starting point is “typical” opening windows.  The open area requirements and opening directions can influence the ventilation rates and the sound reduction provided from external noise sources. Typically a reduction of 10-15 dB is quoted as the difference between external freefield levels and internal reverberant levels for partially open windows.  In practice, the range be greater than this, depending on the open area required and the location and type of incoming sound field.  Further information on traditional open windows can be found in the Napier University Technical Report on Sound Insulation through ventilated domestic windows.

Various types of opening windows enabling natural ventilation with enhanced sound insulation have been acoustically tested in Denmark

A large body of research has been conducted in Denmark, with a major report being published in May 2017 entitled “Open windows with good sound insulation”.  This contains detailed information on different approaches to increasing the sound insulation of opening windows, including secondary glazing with an attenuated plenum providing the air path, and external “sound shutters”.  The work is arranged around the Danish requirement for a natural ventilation free area of 0.35 m2, although the authors note that some of the solutions restrict the air flow and hence impede mitigation of overheating.  [We have translated the text into English – this is now available here].  Further details of various types of windows that have been tested can be found in the Apex Acoustics paper ‘Methods of controlling noise levels and overheating in residential buildings’, ICSV24, 2017.

Sound absorption to balcony soffits can reduce the noise impact on the facade

Balconies can reduce the noise levels impacting on natural ventilation openings in the façade; this is acknowledged within the ProPG text. The range of effect of standard balconies is determined by the location of the balcony (protruding or within the building footprint), whether the balustrades are solid or open, and whether there are absorptive or reflective finishes on the soffit.  Several papers have been produced based on both measured and predicted levels, and improvements of up to 10 dB can be achieved.  More recent studies have looked at partially enclosed balconies, sometimes referred to as winter gardens, and these can provide even greater improvements.  However, fully enclosed winter gardens can have a negative impact on other indoor environmental quality factors such as daylight and sunlight. Our ICSV24 conference paper provides references to these relevant studies, and further information is available in Annexe C of BS EN 12354-3, as illustrated below.

Extract from EN 12354-3 illustrating the factors influencing the noise reduction provided by a balcony

Another option with balconies is to create a convoluted path horizontally, by staggering the openings, as illustrated below.

Staggered air path to allow natural ventilation with less noise ingress

An alternative to these methods, which all use open glazed windows, is to separate the function of providing a natural ventilation air path from the glazed window itself.  Attenuated ventilators can provide large equivalent open areas, and give the ventilation benefits of an open window, but with enhanced levels of sound insulation.  These have been used successfully on several UK projects, achieving a level difference of up to 27 dB from external to internal noise levels while providing natural ventilation to control overheating.  Further details can be found in the Apex conference papers below.

NW Cambridge, Lot 5: The grilles on the left of the windows cover the vents, and note the sliding external shading
Internal grille beside opening doors covers an attenuated air inlet enabling natural ventilation. It is controlled with a motorised damper within the wall, to achieve good thermal performance when closed.

 

Conlan, N., Harvie-Clark, J., Apex Acoustics (2017). Methods of controlling noise levels and overheating in residential buildings, 24th International Congress on Sound and Vibration, London, July 2017

Conlan, N., Harvie-Clark, J., Apex Acoustics (2017) Challenges of using passive ventilation to control the overheating of dwellings in noisy environments, 38th AIVC – 6th TightVent & 4th Venticool Conference, Ventilating healthy low-energy buildings, Nottingham, UK, September 2017 [available when published at conference]

Birgit Rasmussen, Experiences with sound insulating open windows in traffic noise exposed housing, Internoise 2015

More Danish work available here.

International Energy Agency, Energy in Buildings and Community Programme (IEA-EBC) Ventilative Cooling: State-of-the-Art Review, Annexe 62

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Noise, ventilation, and overheating

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