As a main element to most buildings, the glazed openings have long played a key role: contributing natural daylight and ventilation, as well as being integral to overall energy performance, both in terms of thermal insulation and solar gain. Arguably, however, it is in respect of their acoustic performance that the bar is continuing to be raised most dramatically, in response to the growing impact of noise pollution on our everyday lives.
Noise pollution is arising from higher traffic volumes, expansion of rail and air travel and a growing tendancy towards a non-stop society where the population lives, commutes, works, shops and seeks entertainment in ever closer proximity.
This can be detrimental to the quality of life available to building occupants: excessive noise from traffic and transport networks can induce stress, affecting health and wellbeing, but it can also lead to lower productivity and slower learning. There are consequently critical economic and wellbeing benefits to reducing noise in buildings.
Reducing noise pollution in new buildings can be partially achieved by methods such as site-specific assessment of the sound environment, with acoustic mapping of the site used to refine building orientation, layout and position. This will in turn influence capital cost and eventual patterns of occupancy.
However, when it comes to the design of the facade there are particular areas that have to be meticulously considered. For commercial properties the facade, including its glazing, is second only to the building services package in value; normally accounting for 15% to 25% of total construction cost. Therefore, when it comes to the acoustic design of the facade it is of vital importance that it is correct the first time.
The official guidance regarding acoustics for the design process is provided by BS 8233: 2014, taken in tandem with other authoritive documents such as LEED or BREEAM, which is regarded as the most holistic measure of a property's environmental credentials.
To ensure adherence it is important for an acoustician to conduct a detailed survey, measuring the noise levels on the projected footprint, at multiple points and at different times. Each level of the building must be assessed to determine the degree to which the facade system and its glazing elements must be specified: taking account of the minimum attenuation required to deal with the noisiest periods. This may be in order that bedrooms permit people to sleep undisturbed, or for offices to provide a comfortable and productive working environment throughout set operating hours.
The next stage in achieving good acoustic conditions within a building is to understand how the control offered by different materials or elements to envelope, can be compromised by their interconnections or the surrounding structure.
The phenomenon known as flanking sound or flanking noise, refers to the energy waves which pass over or around, rather than directly penetrating a barrier. So, although an insulating glass unit or architectural glazing system may offer good acoustic insulation, noise can still penetrate to the building interior, or pass between spaces.
The systems provider and facade consultant must therefore seek to address rigid connections, especially metal-to-metal interfaces, in order to prevent sound waves being transmitted through pressure plates, frame profiles, joints, brackets and anchor points. Flanking noise can therefore be reduced greatly by careful detailing, such as acoustic infills to mullion and transom profiles and creating additional acoustic barriers between the frame and floor slabs.
It is therefore essential to ensure the window, door or curtain walling system chosen features an effective acoustic seal, together in tandem with effective sealing for guaranteed air tightness.
The choice of glass type and dimensions, including that of the cavity, impacts dramatically on the level of acoustic performance that is achieved. Industry standard double glazing will deliver in the region of a 30dB to 35dB reduction in sound against normal passage through air.
This can be improved upon significantly through specifying thicker panes and special acoustic grade glass, and widening the cavity or by introducing secondary glazing. Rather than this being a linear improvement, every three decibels achieved represents a doubling in performance. And just as combining varying densities of material is effective at combating sound transmission, the best results for glazing units are obtained when the inner and outer panes are of different thicknesses.
It should also be assessed whether to include a laminate interlayer for enhanced acoustic performance - potentially also improving thermal efficiency and safety - or perhaps to go from double to triple glazing. In addition to increasing overall unit thickness, the latter raises glass cost by some 50%, and the additional weight may move beyond the capacity of the framing system originally considered.
By contrast, specifying an interlayer might add 60% to the total material cost, but improve project feasibility through slimness and lower weight. Two smaller opening lights could be considered instead of one, though this has an obvious impact on sightlines.
Developing a relationship with an aluminium systems manufacturer can be invaluable. The expertise available at TECHNAL extends to the crucial planning and previsualisation stages of development as well as being available as an ongoing source of advice during fabrication and installation. With technological innovations such as acoustic test laboratories, sound calculation software, and the renowned Hydro Technology Hubs, TECHNAL is making expertise available to its customers and clients at the earliest possible stages of the design process.
Possessing the right information and by taking a collaborative, cohesive approach from the beginning can lead to fewer on-site issues, improved programme certainty and continuing client confidence.