Secondary Glazing and Reducing Noise from Traffic, Airplanes,
Pedestrians, Pubs and Clubs
Secondary Glazing is a special type of glazing
construction where an additional pane of glass is added to the inside of
an existing single-glazed window. Secondary
glazing is often used for SOUND INSULATION – especially if your existing
windows don't need replacing or where there are planning restrictions on replacement
windows.
Secondary Glazing provides better sound reduction as well as heat insulation
than standard single-glazed windows and many would consider it essential for
houses close to busy roads or other high noise generating objects.
When considering windows there are generally three options available for maximum
achievable sound attenuation (reduction):
Laminated Glass is also a type of safety glass that will hold together when
broken.
Airport windows for example, may have laminated glass on both sides of an
Insulating glass unit in an aluminum frame and with a maximum airspace between
the panes of glass.
When dealing with sound performance of any material there are three things
to consider. This does get a bit TECHNICAL ;-)
These are density, stiffness and damping. There is also a little thing called
the Mass Density Equation that applies specifically to sound attenuation:
1. The transmission loss is increased by 6decibels (db) each time the frequency
of a measurement or the mass per unit of a single layer partition is doubled.
2. By increasing the mass per unit area by a factor of 4 you can increase
the sound transmission loss of a partition, at all frequencies, by 12db.
3. An increase of sound transmission loss to 18db requires that the mass per
unit area of the partition be increased by a factor of eight.
Windows are rated as to their ability to reduce or attenuate sound based on
Sound Transmission Class (or STC). STC is an average of an objects ability
to attenuate sound across the entire sound frequency spectrum. It is also used
to rate interior walls, ceilings/floors, doors and exterior wall configurations.
STC does not provide specific frequency-deadening information, which may be
what is needed if you want to block a specific type of unwanted noise that
operates on a high or low frequency.
Higher frequencies are much easier to attenuate than low frequency noises.
This means that our secondary glazing may be able to block high pitched music
but not be as competent at reducing low pitched sounds such as the bass sounds
in music or the traffic driving along the street outside your house.
WHAT ABOUT TRIPLE GLAZING – WILL
THAT BE MORE EFFECTIVE?
Many people would advise that triple pane glass would have a greater sound
deadening ability. Unfortunately, triple pane glass only offers a very slight
enhancement over standard double pane at lower frequencies due to the additional
density of the additional pane of glass. Overall there is very little difference
in the Sound Transmission Class rating between triple and double glazing provided
that the overall airspace between the panes is constant between the two constructions.
For example: consider a triple pane with two 6mm airspaces and double glazing
with single 12mm airspace. Both of them are using 3mm glass, the STC will be
identical if the IGU's are the same dimensions.
Using one thicker (e.g. 6mm) and one thinner
(e.g. 3mm) pane of glass in an IGU may also help deaden sound because each
pane of glass is "transparent" to
a different frequency and each piece of glass will then attenuate the frequency
that the other pane of glass "passed".
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Saving Trust ~ Access
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