DWV expansion joints

[Xenomorph]

I am not familiar with using expansion joints, so I am hoping the more experienced plumbers here could enlighten me:

1) Are they used to guard against movement in the ground, roof, or both?
2) Where are they placed...at the bottom of a stack?
3) Should every stack have an expansion joint?

Thanks for any info you guys can provide.

[hj]

1) Are they used to guard against movement in the ground, roof, or both?

Their primary usage would be in vertical stacks that would be subject to expansion/contraction forces.

2) Where are they placed...at the bottom of a stack?

Wherever the expansion/contraction would occur, namely between any two points that are securely anchored so that any E/C forces would create a stress.

3) Should every stack have an expansion joint?

No. Their usage is normally limited to long risers in tall buildings, and even then the E/C is usually accomodated by offsetting the stack periodically.

To answer your unasked question. About the only houses that need expansion joints are log cabins that are subjected to shrinkage as the logs age. In that case, the floor to floor dimension will change over time and if there is no provision to handle it, the upstairs toilet would be lifted off the floor and the piping would have to become distorted. (Doors and other items also have to have provision for the shrinkage, because any wall openings will also get shorter.)

[jimbo]

I saw a very interesting show on TLC or one of those channels, about building what was hardly a log CABIN but more like log MANSION. They have some very creative techniques to deal with the shrinkage. Many components like doors and window, are essentially installed in a sleeve arangement, where the wall can settle down around the casing, the window doesn't move and isn't crushed. I don't remember exactly how they did the plumbing, but again the whole idea was to not attach things like pipes to the structure that was going to settle.

I imagine that even with such techniques, this is just one of the things you have to deal with over the years in such a house. It was a biggy, two stories, probably a few thousand square feet.

[Xenomorph]

Thx again HJ, you really cleared things up for me