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Everything that I have read and my past experiences indicate that cast iron waste lines and copper drain lines perform the quietest.
The cast iron/copper combination is also just about the most expensive combination to use in a house. Does anyone out there have any experience with plastic pipes and sound deadening them? Is it economically feasible or just a pain in the butt exercise? I can still remember being on the ground floor of a plastic plumbed house when the upper floor commode was flushed – it sounded like a miniature Niagara Falls – no lie!!! The idiot architect also put the main stack right down the middle of the living room wall which was also shared by the central hallway. Talk about a boo-boo.
Looking forward to your responses,
Cliff. Johnston
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For DWV you don't have to use all one or the other. Consider branch stuff on first floor in plastic and use cast with no-hub fittings for bathrooms from the second floor.
I'm not so sure about copper being quietest. Probably galvanized is but today I'd look at pex.
Plaster or veneer plaster walls or even 5/8" gwb will help attenuate mechanical system noise. Generally mass - as in cast iron, galvanized, and plaster - provide the most certain benefits to noise attenuation.