Making a noise about insulation
Roseview director Paul Bygrave argues that while the industry has already cracked energy efficiency, acoustic insulation could be the next big thing.
Our industry has spent years working on the energy efficiency of windows, with incredible results: modern windows are A-rated as standard; coatings, argon gas and warm edge spacers prevent heat loss through the glass; multi-chambered profiles, thermal reinforcing and breaks ensure frames do the same; and ultra-clear low iron glass increases solar gain.
As a result, U-values have tumbled; you can see how far simply by checking the changing Part L of the Building Regulations. In 1990, the maximum permitted U-value for windows on new builds was 4.8W/m2K. By 2000 that was down to 3.1W/m2K, and in 2010 it was 2.0W/m2K. Today, the requirement is 1.4W/m2K, a level that’s easily achieved by most modern windows.
But progress is slowing as scope for further improvement diminishes. More improvements can always be made – triple glazing still has potential, krypton and xenon can replace argon, and vacuum IGUs are on the horizon. But these are expensive, in some cases controversial, and don’t offer dramatic improvements. For now at least, the results don’t always justify the costs.
But as progress on thermal efficiency slows, a new area has emerged that could demand similar attention: noise reduction.
As pressure to provide more housing increases, we’re seeing more developments in high noise locations. Town centre office conversions, plots adjacent to railway lines, flight path developments – all are on the increase. Simultaneously, there’s pressure to improve infrastructure. The third runway at Heathrow, HS2, and several major road improvements are examples of the countless projects that bring noise closer to people’s homes.
While noise reduces naturally over distance, over short distances that reduction isn’t enough. The inverse square law states that doubling the distance from a noise source reduces that noise by 6dB. For instance, an ambulance siren that’s 120dB from 2m away will still be 100dB from 20m.
Ultimately, developers and installers have to provide an effective barrier to noise at the main point of entry on a building – the windows.
A typical original single-glazed window will reduce noise by around 20dB. Like the 1990 U-value regulation of 4.8W/m2K, that’s not very much. But while modern windows have seen big improvements in thermal insulation, for acoustic protection it’s not so striking.
Standard modern windows typically provide between 30dB and 35dB of noise reduction. Even when enhanced with acoustic glass and triple glazing, that’s unlikely to go much beyond 40dB. Set against the levels of a busy road (around 80dB) that leaves 40dB-50dB, which exceeds the World Health Organisation advisory levels for living and office space. It simply isn’t enough.
Secondary glazing is a traditional product, but correctly fitted, sealed and set 100mm from the internal face of the primary window, it can improve external noise reduction by 45dB. That’s on top of the reduction offered by the main window. Added to the 20dB from an old primary window, or the 35dB modern glazing provides, you get an overall reduction of 65dB-80dB, which is more than enough for almost any location.
The number of projects with demanding acoustic requirements continues to grow. That will drive further development, making windows a more effective barriers to noise, just as they have become for heat loss. It has already started, with acoustic glass pushing sound reduction up from the low 30s to low 40s.
But there’s still some way to go. Noise reduction of 40dB is currently relatively simple to achieve. But in old buildings where aesthetics are critical, or when a higher level of noise reduction is required, options quickly become limited.
Aluminium secondary glazing is a high-performance yet cost-effective solution. It’s simple to survey and install and yet provides excellent acoustic protection, while leaving the external appearance of a building untouched.