Noisy PVC Plumbing Drain Pipes – Cast Iron Solution

DEAR TIM: We just moved into a 15 year old home. Every time we flush the second floor toilet, we hear water running down our living room wall. The wall is never wet and I can find no leaks in the basement. What is happening to the water? B. B.

DEAR B. B.: Relax, the water is going down the plumbing stack and on its way to the sewer. Since you do not see any evidence of a leak, your description of the problem leads me to believe that your plumbing drainage system is constructed of PVC plastic piping.

PVC piping is notorious for sound transmission. It's low density plastic makeup makes it very noisy. Often you can hear a small amount of water trickling down the pipe. You can identify this type of pipe very easily. It is non-metallic, white, and often has labeling imprinted on the pipe which states that it is PVC.

You can solve your noise problem with a little bit of work. You have basically two choices. If the piping is PVC, you can replace it with cast iron piping. Due to its dense structure, cast iron piping transmits very little noise. This is one reason why you rarely hear water rushing down the walls of older houses. Cast iron drain piping was the material of choice 80 to 100 years ago.

This choice will probably be expensive due to the fact that you will be removing existing drainage piping and replacing it with new piping. Also, in most cities and states, work of this scope requires the services of a licensed master plumber to perform the installation.

Installing cast iron in a new house or a remodeled bath is not a budget breaker. Often it can be added to a house for only a $150 per bathroom. Remember, only the pipes that carry water need to be cast iron. All vent pipes that deliver air to the plumbing system can still be PVC.

The other alternative is to expose the piping and insulate it with fiberglass sound batts. Be sure to wrap the entire pipe, starting at the base of the toilet and continue until the pipe enters the basement. Then fill the rest of the wall and ceiling cavity with sound batt insulation.

When you have finished, flush the toilet before patching the wall. If you still hear the water, locate the source of the noise and add more insulation.