Laboratory and Field Research Show Cast Iron Soil Pipe with Elastomeric Gaskets Produces the Quietest DWV System

Builders and designers realize that plumbing noise often irritates property owners. The inconvenience, excess costs and strained customer relations that result from retrofitting a DWV (Drainage, Waste and Vent) system can be avoided by specifying the correct materials to be used during initial construction. The key is to understand which materials result in the quietest DWV system.

Noise in DWV systems is the combined result of the vibration of the system and of airborne noise passing through the pipe wall. To provide quantitative information about the problem, Polysonics Acoustical Engineers of Washington, D.C. tested various materials commonly used in the construction of DWV systems.

The following graphs illustrate the noise suppressing performance of these popular DWV materials. The recorded data reveal vibration reductions as high as 12 decibels per joint in hub and spigot cast iron pipe, and as high as 9 decibels in hubless pipe with elastrometric gaskets and stainless steel shields. These figures are particularly meaningful when one considers that the human ear can detect a sound level of 3 decibels; so cast iron hub and spigot and hubless materials result in vibration reduction four and three times greater per joint, than our ability to detect those vibrations. ABS and PVC thermoplastic piping materials show no meaningful vibration reduction across joints. Cast iron pipe and fittings clearly "out-silences" these plastic piping mateials.

In addition to the vibration reduction across joints in a cast iron DWV system, the cast iron material in the wall of the pipe and fittings serves to deaden airborne noise of running water, which exists within all DWV systems. Cast iron owes its noise deadening characteristics to the dense molecular structure of iron, which inhibits the passage of sound waves through the wall of the pipe. Once again, cast iron pipe and fittings "out-silence" plastics.

When a DWV application calls for quiet system operation, there is only one choice. Cast iron is by far the quietest pipe of all.