Edinburgh Napier University

  Planning guidance is required to advise on appropriate standards against which the suitability of development can be assessed. Consideration is needed of the locale, its
existing character and of future residential amenity. In the noise context, advice is primarily required to define threshold exposure levels relative to extraneous sources of environmental noise. A thorough knowledge of the acoustic transmission characteristics afforded by the building envelope is therefore desirable to assist in the setting of threshold levels and to aid in the design and verification of development
proposals.

The insulation of an open window has been generally accepted as being 10-15 dBA although its precision and affect on opening style, open area and window size, are
not readily available. A programme of laboratory measurements have been undertaken by the Building Performance Centre at Napier University on behalf of the
Department for Environment, Food and Rural Affairs, in order to quantify the sound insulation provided by a variety of window types, opening styles, areas of opening
and ventilator devices.

Open Windows: The test regime measured the sound insulation provided by seven separate windows, with a combination of twelve different opening styles. The
variation in weighted level difference, Dw, across the different opening styles for approximately equivalent area openings has been consistently measured as between 4 and 6 dB.
The range of measured insulation ratings, for window with a free open area of 0.05 m2, is Dw 14 – 20 dB. This translates to the following dBA level differences, due to variations in the source noise characteristics:
• Road Traffic Noise 12 –18 dBA
• Railway Noise 12 –18 dBA
• Aircraft Noise 14 – 19 dBA
• Amplified Music 15 –20 dBA

The window results do not show any one opening style which provides significantly better insulating characteristics. In general the set of windows with an outward opening light performed well. The windows with no extending opening lights, namely the internal turn and tilt and the sliding sash, were also among the best performing open units; particularly when the source of noise was neither random nor normal incidence. Variations in the window size, frame material and glazing type have little significance on the insulating performance of an open window.

Closed Window. The introduction of a ‘closed’ 4000 mm2 slot ventilator within the window frame reduced the overall weighted insulation performance of the window by 6 dB. This reduction increased to 11 dB when the vent was in its ‘open’ condition.

Proprietary over frame vents gave a marked improvement in the high frequency acoustic performance; however the weighted insulation rating is generally dominated by low-frequency transmission which is not substantially improved over that of a slot vent.

Sound Directivity: Rotation of source incidence away from the normal, within a nondiffuse acoustic environment, is found to consistently improve the resulting open window façade insulation.