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john4153 10-05-2011 07:51 PM

Expansion joint
I have discovered a small and strange leak in the waste lines for my new home, built originally in 1993. It is a log home and the plumbing is ABS. In late Summer, I discovered a small leak at the hub of a 3" line going to the main vertical waste stack. Imagine a T. One side of the cross serves the master bedroom. The other cross serves the guest bedroom. Both bedrooms are on the 2nd floor. The vertical line goes from the 2nd floor to the basement and exits through the basement floor. I had not used the bath or toilet in the guest room until this time. The connecting joints were all concealed in a cabinet. I opened that and found the leak. It leaked about a tablespoon or two of water over the course of a day after flushing the toilet. It seemed to come from right where the horizontal pipe entered the hub of a wye to the vertical stack.

Both arms of the T go to toilet flanges that are very close to the vertical pipe. The resulting connections are rigid. I cannot wiggle the wye's or bends at all. In the course of tracing the leak at the joint, the weather turned cold (20 to 30F drop) and it stopped leaking. There are no expansion joints or rubber connections in the drain system.

Right now, I am working on two assumptions:

1) Expansion during the hot period caused strain on the joint to open a hairline crack. With cold weather, that closed. So far, I have not turned the heat on in the house and it is quite cool, say 50 to 60F.
2) My probing to find the source of the leak moved a flake of ABS that sealed the leak, at least temporarily.

I have added a fluorescent dye and will check that tomorrow. Also, we are back to a little warmer weather.

I am pretty ignorant about the use of expansion joints, but I find them advertised on various log home sites, because logs settle.


1) Must expansion joints be used only in vertical lines? When installing, is there a rule of thumb for how compressed or expanded they should be? It is a 3" waste line.

2) Can rubber couplings be substituted?

3) Can rubber couplings be used for horizontal runs?

4) Is my theory that this is temperature related completely crazy? Would you just repair the leaking fitting and forget about adding an expansion joint?


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