Cast Iron is the silent solution

Cast iron has once again, been proved to be the modern drainage material of choice. Its exceptional sound-deadening qualities won the day in independent plumbing noise tests in Australia and the USA.

Down under, it demonstrated its silent superiority over steel, PVC and other lighter weight materials. And in America, it was awarded the title of the quietest soil system against rival PVC-U and ABS systems.

But the Cast Iron Drainage Development Authority (CIDDA) stresses that this is only the start of cast iron’s success story in an application environment which, in the UK at least, is widely misunderstood, easily over-complicated and, until new yet-to-be approved detailed regulations take effect, poorly superintended.

What exactly is plumbing noise?

The evacuation of waste, soil and rain water naturally generates both structure-borne and airborne sounds between rooms. Such noise, especially in blocks of flats, usually occurs as the result of a mixed flow, when the pipe is filled with a mixture of watered and air.

A pipe carrying mixed flow will radiate noise outwards and carry the noise to any lightweight ceilings, cupboards and similar areas wherever the pipe makes contact.

What do the regulations say?

UK regulations for noise control in residential buildings are not as explicit as some overseas markets. Guidance is given for wall and floor types but little is offered in the way of recommendation for waste, soil and rain water pipes within the fabric of the building.

However, the proposed regulations make it clear that noise control is slowly but surely creeping up the agenda to gain equal recognition with other vital building issues like fire safety.

Who says cast iron is the quietest material for above ground soil waste systems?

The Building Code of Australia has specific requirements for constructions surrounding soil and waste pipes.

A series of tests carried out by the National Acoustic Laboratories in Sydney compared the sound power radiated from cast-iron soil pipes with that radiated from steel, PVC and other lighter weight materials. The following table gives predicted sound pressure levels in furnished spaces for a number of typical situations.

Table 1: Noise associated with Waste Pipes, dB(A)

Pipe Material Stainless Steel PVC HDPE Cast Iron
Sound power level radiated from pipes 68 69 71 55
Sound pressure level in funished room        
 - No ceiling 58 59 61 45
 - Plasterboard ceiling 29 32 35 19
 - Acoustic tile ceiling 43 45 48 33

The effects of standard lagging materials were also assessed. The results found that noise radiated from unlagged cast iron pipes is close to or less than that from lagged alternative pipe systems (depending lagging type). For conventional thermal lagging of fibreglass or Rockwool with Sisalation facing, unlagged cast iron pipes are 4 dB(A) to 7 dB(A) quieter than lagged pipes.

DWV vote unanimous for cast iron

Noise in Drain, Waste and Vent systems is the combined result of system vibration and airborne noise passing through the pipe wall. To gather quantitative information about this problem, Polysonics Acoustical Engineers in Washington DC tested various materials commonly used in DWV systems construction.

The results illustrated the noise-suppressing performance of popular DWV materials and revealed vibration reductions as high as nine decibels for hubless pipe with elastrometric gaskets and stainless steel shields. ABS and PVC thermoplastic piping materials showed no meaningful vibration reduction across joints.

Nicola Hughes of CIDDA comments "Nine decibels make even more sense when you realise that the human ear can detect a sound level of three decibels. So hubless cast iron reduces vibration three times more than our ability to detect it. Which should silence the plastic pipe advocates once and for all."

For more information or a datasheet containing a detailed summary of the independent tests mentioned above please contact CIDDA at Wyatt House, 72 Francis Road, Edgbaston, Birmingham, B16 8BR.

The CIDDA hotline number is 0121 693 9909 or you can visit the website at www.cidda.com
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