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Internal building noise, particularly from water and waste water drainage systems is an increasing issue, but boxing and insulating pipework is not the most cost-effective answer, says Chris Ricketts, a Product Group Manager at BSS Industrial.
How many times have you been in a public building like a school, hospital, library or a hotel and had your concentration, or even worse your sleep, disturbed by a flushing toilet and the sound of water rushing through pipes to refill a cistern?
Most people would probably blame it on paper-thin walls, but the reality is that modern building methods are creating environments which retain and reflect noise. Better soundproofing of the outer-building shell, lightweight construction inside and a requirement for airtightness all combine to exclude external noise and contain internal noise.
The problem is further exacerbated by open-plan layouts, in conjunction with marble or laminated floors, which reflect sound, and a lack of carpets and curtains which can absorb noise. The effect can be considerable, particularly on people’s ability to concentrate, work or rest.
Response to noise
The human response to noise is complex and is dependent upon the activity we are doing for example whether we are working, sleeping, listening to music or enjoying a party. If the sound is 10db higher than the background noise it becomes the dominant noise. We have all had the scenario of where we have suddenly focussed on a noise, such as rain running in an internal stack and, once tuned, in we cannot remove it from our focus.
All noises above a 25 decibel level (dB) will generally be noticed by an individual with normal hearing and in general people require a sound level below this to sleep. The range 35-85dB is regarded as intrusive and restrictive for intellectual work.
Drainage generally falls within this level. A toilet flushing or a tap running into a sink can produce a noise between 55-85dB which is enough to disturb concentration and interrupt sleep in a hospital.
Within an occupied area whether it be a hotel room, hospital ward or apartment, noise generation will emulate from the central soil, vent and internal drainage stacks as well as the appliances. CIBSE’s Public Health Engineering Guide stipulates the use of product specifically designed for sound reduction whilst the Building Regulations require acoustic treatment to downpipes in habitable spaces and recommended constructions to combat sound transference. This is all well and good, but in reality the achieved construction’s insulation abilities will be significantly poorer than the design, due to flanking paths, air gaps and fixing bridge points.
The answer lies with drainage system design, with the ultimate aim being to protect neighbouring rooms from intrusive sound, be it airborne sound or solid-borne sound which travels through the building fabric.
Noise protection
One of the keys to protecting neighbouring rooms is to de-couple the source of the sound from the construction. This can include the detachment of the toilet from the wall to reduce solid-borne sound via the use of lightweight pre-wall constructions.
Sound attenuated drainage systems are highly suitable for the lightweight dry-lining constructions utilised today because of its airborne sound insulation values with no need for additional structure borne insulation. The pipes are fixed using appropriate structure-borne sound insulation pipe clips. However, sound bridges must be avoided during installation.
In terms of piping, there are two methods of insulating against airborne noise. The first method, cavity absorption, involves the use of a duct wall and a sound absorbing material surrounding the pipe. The problem with this method is that it can take up valuable square footage space which cannot be either utilised or rented. An alternative method is the use of a foam acoustic wrap around the pipework.
Nowadays there are also many soundproof piping products available which boast increased mass to dampen sound. Many have hydraulically optimised fittings, to increase flow and avoid turbulence in the system, and also ribs which provide a noise dampening effect.
Sound proofing
Critically, it is important that the entire drainage system is equipped with noise dampening materials as there is little point in using soundproof piping if it is attached using non-soundproofed fittings and bracketry.
For example, many drainage systems on offer from manufacturers utilise special clamps with a custom made rubber layer and also soft-lagging where pipes run through walls and ceilings or are embedded in concrete and masonry.
A vital issue is the noise created by foul or waste water rushing around bends in pipework, which can dramatically increase noise levels.
Where significant bends cannot be avoided there are a number of acoustic lagging products available which can dramatically reduce noise. The use of an acoustic product on a 90 degree piping bend can reduce noise from approximately 48dB down to a more manageable 36dB.
Total cost
One final critical point is that it is important to take into account the total insulation cost when designing a drainage system. Specialist acoustic drainage systems, manufactured by companies like Geberit, Durapipe and Polypipe and available from BSS Drainage, provide significantly lower installed costs over cast-iron, lagged PVC and HDPE once the cost of boxing-in insulation and lagging are taken into account.
As the consumer becomes ever more sophisticated, there is an ever increasing pressure to improve standards in public buildings in their various formats. As such, traditional ways of achieving sound attenuation will become increasingly redundant.
