HERITAGE WINDOWS: REDUCING NOISE .

The first step in tackling noise ingress from windows and doors is to ensure effective draught seals are fitted. Draught seals not only reduce draughts but also reduce the air bourne noise & dust by reducing the air flow from outside. An unsealed window is comparable to a partially open window; fully closing it will cut noise and draughts by reducing the air flow! Many people find that simply addressing this air bourne noise with draught seals improves the situation to an acceptable level. If further improvements are required then the glazing should be looked at next.

Secondary glazing might be considered as it is a viable, effective option. However most secondary glazing systems are not in keeping with period properties, not only detracting from the appearance but also making operation of the windows difficult.

We are receiving more and more requests to install acoustic glass (audio screen) into traditional timber windows. This audio glass is available in many thickness designed to control various levels and types of noise. Developed by the larger glass manufacturers and tested in laboratorys; the results are impressive - on paper! In our experience the test figures do not often transfer into a cost effective real life improvement when used in existing traditional timber windows.

Noise travels in waves of varying frequencies. eg. Low range noise such as the rumble of a passing truck or high frequency noise such as a whistle. High frequency noise is much easier to control than the low frequency 'rumble' because of the shape of these sound waves. Sound insulation materials attempt to control noise by disrupting the flow of sound waves. Every time the wave passes through a barrier it is diminished and the shape of the wave is altered. Acoustic glass is comprised of 2 or more layers, laminated together with a special film separating the layers. As the sound waves passes through each layer it is diminished. Laminated safety glass is also manufactured using similar methods.

The acoustic glasses are available in a variety of thickness, with 12.8mm being the thickest to sensibly incorporate into traditional timber windows. With an increase in thickness comes an increase in weight. If used in an existing sash window this additional weight must be offset by replacing the original iron weights with lead. The thicker the glass the more lead, which usually results in less functionality as the window opening size usually has to be reduced. The pulley's must also be considered as they carry the combined weight of the frame and the counter balance weights. Often pulleys must be replaced with the more expensive ball-bearing varieties.

At Sash Window Specialist we see this as a law of diminishing returns. With each step up in the glass thickness, the greater the expense, for marginally better sound insulation. Often money could be redirected elsewhere to counter the problem of sound 'leakage' from other areas. Ceilings, floors, chimneys & walls are all sources of noise intrusion that should be considered as problem areas.

Laminated safety glass of 4.4mm or 6.4 mm thickness offers improved sound proofing over standard glass, at a fraction of the cost of specialist acoustic glass. The counter-weights might still need to be changed or supplemental lead weight added, but the project costs are far less. Laminated glass is also a very good security upgrade as it is difficult to smash a hole through. In our opinion this is the most cost effective solution for the majority of situations.

Double glazed units are a wise choice for controlling noise intrusion. We recommend using different thickness glass for each pane. As the sound waves passes through the outer layer it's form is changed and diminished, it then passes through an air gap before encountering the inner pane where it is changed again and diminished further. This varying of the thickness offers an improvement to the noise levels experienced inside the property. Incorporating a laminated glass into the double glazing obviously improves the sound insulation further.

At Sash Window Specialist we can supply double glazed replacement sashes or re-glaze your existing windows with glass of your choice. However we recommend that you study the manufacturers published figures and consult an acoustic specialist prior to fitting acoustic glass into heritage properties.