Hello everyone,

We're nearing the end of an extensive renovation/reconstruction project where a three storey house, previously divided into three units, has been converted to two units (owner and tenant). The owner unit comprises the basement and first floor, the rental unit the second and third floors.

All of our walls are up and boarded, etc, and we've just installed our first toilet on the third floor. There's a problem though. It creates a great deal of noise in the first floor.

The four-inch waste stack passes down from the third floor, through a wall in the second floor (under which the kitchen sink/laundry/etc is connected) and then through a wall in the first floor. The run is a straight drop and I think it is almost perfectly plumb, which I think may be our problem (the waste water is dropping and sloshing around). In the basement ceiling it turns and runs into the utility room. The noise there is not a concern.

What do we do to eliminate the sound on the first floor though? The wall is constructed of two-by-sixes, we did insulate around the stack but it almost touches the backside of the drywall.

We're sure we're going to have to expose that bay either way. Are we doomed to add some turns into the stack or are there other products that can dampen the sound? Does spray foam work?

Thanks!