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edlank 03-23-2009 07:23 PM

Drain line thermal expansion ticking
I bought a house built in 1990 which has plastic drain lines. The bathroom drain line runs across the width of the house in the joists below the second floor. The horizontal run is about 35 feet. When someone takes a hot shower, the drain pipe makes a loud ticking as I would expect from thermal expansion. It is pretty objectionable. If I were to try to do something about it, I am guessing to expose it at the side wall where it makes the turn to go down beside the first floor wall is the most likely place it is under compression. If I can relieve the cramping that is where I am likely to find it. Right?

The ticking eventually ends if more showers are taken, but it persists for minutes with the first one.

Where this pipe leaves the side wall and enters the unfinished basement, and becomes visible, it is 4" schedule 40 pipe. It should be suspended with metal strapping up in the joist space, shouldn't it, with a gentle grade of about 1" per 10'.

The other upstairs bathroom also does the same, but much less loudly.

Unfortunately, this house has crown molding on the first floor, where I think I need to access the drain pipes. That means it will be considerably more work to repair any holes I create.

inspectorD 03-24-2009 05:23 AM

The ticking is from thermal expansion. Usually from the hangers which support the pipe, or from rubbing against any wood next to it.
You should not use metal straps for plastic lines. They wear the pipe out and cause leaks over time from the movement. Go to your plumbing supply house in your area and tell them the issue, not the big box stores. They make hangers for this issue.
Good luck.

edlank 03-26-2009 06:18 AM

Thanks for the response. The ticking is so loud, I cannot imagine it comes from sliding of the pipe in a hangar strap. I suspect the pipe is sliding against a joist. I wonder if the right angle to turn down the wall is tight up against the side wall and under considerable compression when it expands. I will try to localize the origin of the sound...I do not want to create many holes in the ceiling.

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