11.4.8 Sound Control Glass
Glazing and windows play a critical role in the sound insulation of a building, and are frequently highlighted as the most vulnerable element in a building’s ability to resist noise intrusion. By understanding a few basic fundamentals relating to glass and sound it is possible to select a glass capable of providing good sound reduction to control noise. Before exploring the sound reduction capability of glass, it is important to establish the fact that windows will achieve their high performance potential only if all air gaps are sealed. Effectively, this means that the frames carrying the glass must either be fixed or incorporate seals all around. In addition the glass sound rating must be in balance with that of the structure as sound will enter through ceilings, carpets, air conditioning ducts etc.
When selecting glass products for acoustic insulation, there are several fundamentals that have a bearing on the sound reduction effectiveness.
- Sound reduction will increase with increased glass thickness, due to the increased mass involved. This is particularly so at lower frequencies.
- Sound reduction will decrease somewhat with increasingly larger glass area, but not generally enough to make a discernible difference in most architectural glass sizes.
- Sound reduction will increase with the use of all laminated glass due to the vibration dampening effect of the plastic interlayer sandwiched between the plies of glass.
- Specially formulated soft interlayer such as used in SoundStop have been developed, which, when cured, produce a laminate interlayer that is softer, more pliable and more elastic than the traditional harder PVB interlayer and thus further increasing sound reduction.
- Multi laminates combine the increased mass effect of solid glass with the dampening effect of plastic interlayers can provide even superior sound reduction.
- Where high sound insulation is required, wide air spaced double windows with airspace widths greater than 100mm may be required. Lining the reveals with acoustic absorbent material is beneficial because it reduces the reverberation in the cavity. Increasing the airspace width produces an increase in sound insulation, but beyond 200mm may become uneconomic for the smaller incremental improvements achieved.
- Sound reduction can be improved by using different glass thicknesses and types in double glass/glazing combinations. This minimises sympathetic vibrations which occur when glass of the same thickness resonates in unison and transmits sound.
11.4.9 Acoustic Laminates
SOUNDSTOP® laminated acoustic glass is a cast-in-place (CIP) laminated safety glass specifically designed to reduce sound intrusion into buildings. It consists of two glass plies with a 1.0mm or 1.5mm acoustic grade resin interlayer. SoundStop has a special acoustic grade resin interlayer that acts as a sound damper, enhancing performance and reducing the effects of sound vibration and the coincidence dip.
For example, loud street noise is rated at 90 decibels and 13.5mm SoundStop acoustic laminate properly installed can reduce the passage of sound through windows by about 38 decibels. The 90 decibels then becomes a tolerable 52 decibels, being equivalent to an average office noise. SoundStop is ideally suited to applications where noise prevents normal conversation, relaxation and efficient working conditions such as in houses, offices, hotels, motels, hospitals and recording studios.
SoundStop acoustic laminate is manufactured to
order and can be glazed into standard aluminium window frames as
long as the rebate has adequate drainage.
Note: Glass is only one element in the sound proofing of a building and other elements such as window frames, wall insulation and ceiling insulation need to be addressed if the expected benefits are to be realised.
Standard PVB laminated glass can also provide good acoustic performance especially if the thicker interlayer options such as 1.14mm and 1.52mm are used. The important difference between PVB and CIP Acoustic laminates is the density of the interlayer. The ‘harder’ PVB interlayer results in the effective mass of the two sheets of glass on each side of the interlayer becoming the sum of the two. With the softer CIP Acoustic interlayer, the resonance coincidence is more closely aligned to the individual components of glass. This results in a higher frequency for the resonance and, in some cases if different thicknesses of glass on either side of the interlayer are selected to help reduce the resonance.
11.5 Risk Control
Controlling the risk of accident or injury for the public and occupants in and about buildings is a primary design criteria. Glass plays a key part in protecting people from injury and this section covers some of the key risk control functions of glass.
11.5.1 Safety Protection
Protection against Human Impact.
Safety glass, or annealed glass of a suitable
thickness and size, is used to provide protection against accidental
injury in glazing locations defined in NZS 4223 Part 3, Human Impact
Suitable safety glass products are:
TEMPAFLOAT® toughened safety glass.
SAFELITE® PVB or CIP laminated safety glass.
Refer to Section 4 and Section 5.
Where transparent glazing may be mistaken for a doorway or unimpeded path of travel it must be made apparent by some form of marking. The marking may take the form of decoration, solid or broken lines, patterns or company logos as defined by NZS:4223 Part 3:1999, Clause 303.1 and is required to comply with the NZBC Clause F2. The marking is not required in housing where safety glass is used.