4.2 Sustainability and Sound Insulation

Sound insulation is not a subject often considered an influential factor during the design stage of green and sustainable buildings. Sound insulation can significantly impact upon the levels of embodied energy in a given building. It is therefore important to have a clear understanding of how sound insulation can affect levels of embodied energy.

Refurbishment
The most effective method of reducing the embodied energy of a given development is to re-use an existing building. Demolition and rebuilding is often justified on the grounds of flexibility and acoustics. Our experience across large and complex refurbishment projects shows that most problems can be overcome and resolved in a cost effective manner. The key to refurbishments is in understanding the performance of the existing building fabric by means of early upfront acoustic testing. Having established the existing performance and understood the limitations and restrictions of a given building frame, design teams can work their way around these restrictions.

Lightweight versus Mass
Heavy/high mass buildings are often favoured on the grounds of enhanced acoustics; however timber and other lightweight framed buildings can often offer equal performance. The advantage of timber/lightweight framed buildings is the considerable reduction in embodied energy with a sustainable building frame and reduced levels of flanking between spaces.
Comparing the acoustic performance of stud to block work, it is seen that both of these systems have a similar performance. Block work does have a better low frequency performance but this is rarely required in modern developments. Timber studs tend to offer lower levels of sound insulation than metal studs, as timber studs are less flexible. This limitation can be overcome by means of using a resilient bar within the partition make up. For comparison, the acoustic performance of walls and floor types are covered over the next two sections.

Mineral Wool within Partitions
Acoustic dampening within stud walls is a cost effective and sustainable method of enhancing the performance of a partition. ISO wool is conventionally used within partitions. This is a quarried product and one which requires considerable heat to turn rock into wool. Damping within partitions can be achieved by most forms of lightweight fibrous or fluffy materials. This means that a wide range of recycled / sustainable materials can be used: recycled carpets, recycled plastic bottles, recycled jeans, Thermo fleece - sheeps wool, Warmcell - recycled news papers, etc.

Performance
As a rule of thumb, a ±6 dB change in sound insulation equates to a halving or doubling of mass of a given construction. Over specifying acoustic parameters can therefore have a significant impact upon waste.

It is often the case that performance standards are copied from one project to another, particularly in the case of office developments. Performance standards are repeatedly misunderstood and hence over specification takes place. Planning conditions are another type of performance requirement that are rarely challenged, which again can lead to over specification. All of these factors results in waste and unnecessary levels of raw materials being used. When designing sustainable buildings it is fundamental to ensure that the correct and most suitable performance requirements are used.

It is important to note that small reductions in acoustic performance levels are often not heard. A small variation or reduction in performance levels can however considerably reduce the required levels of acoustic treatment, remembering the 6dB rule. It is therefore sometimes worth considering downgrading the performance levels of the floors and walls on the grounds of sustainability.

An important rule is that a partition should only exceed the performance of the weakest link by no more than 10 dB. As an example, there is no point in having a partition rated above 40 dB Rw if it contains as 30 dB Rw door. The above text shows that by having tight, accurate performance requirements, waste can be considerably reduced. Hence, it is always worth consulting with an acoustic engineer when considering performance specification.

Specification Design Tolerances & Early Testing
When designing a building, an acoustic consultant will usually include significant design tolerances. One way to reduce the effects of these tolerances is to carry out a programme of early acoustic testing. This is a very good method of ensuring that the design is sufficient and gives enough time for any design tweaks to be made with minimal cost impact on other areas of design. This will allow design tolerances to be reduced with the comfort of knowing that the design will be assessed at an early stage. The benefit of this is a reduction in over specification, resulting in less waste, less embodied energy and less cost to the client.