Expansion loop for exposed 2" copper drain line?

I'll be installing 20 feet of exposed 2" copper, connecting to a backyard sink.

The copper is a straight horizontal run, except at the midpoint there's a short jog laterally followed by a short drop down, where it transitions from the retaining wall to along the house wall, then it eventually elbows into the house plumbing. It will be affixed to the walls using hospital brackets.

About half of the run will be exposed to the afternoon sun; the other half will be shaded by the house.

According to my calcs, the thermal expansion I can expect is 0.18", or about 3/16". But I expect there's also relative movement between the house and the retaining wall to account for.

A normal expansion loop would be a sideways U, but I'm thinking my jog + drop will serve approximately the same purpose?

I'm also considering leaving an unsweated copper connection at the short vertical transition, with a healthy coating of copper anti-seize, and a Fernco tightened only on the top band. I'm hoping that would allow enough movement that none of the soldered joints would be stressed, and would only have the potential to leak if the drain backed up.

Any thoughts on this approach? Any potential pitfalls?

Pictures are always a good thing:



Hospital Bracket:



Expansion Loop:

You are way over thinking a very simple job.

John

That's my MO. What are your thoughts John? Just solder the joint and don't worry about it?

Unless the drain is anchored by seismic struts at the sink, all the "expansion" will occur there. But, I doubt that your sink's water will EVER be hot enough to cause even 1/16" expansion.

hj said:

Unless the drain is anchored by seismic struts at the sink, all the "expansion" will occur there. But, I doubt that your sink's water will EVER be hot enough to cause even 1/16" expansion.

Click to expand...

I'm not even thinking about expansion caused by hot water. I'm just thinking of normal temperature variations, maybe 30° in the winter and 100° in the summer. That's where the 3/16" comes from.

The rest of the run to the sink disappears into an adjoining retaining wall and will be buried plastic, so no concerns there. But since the the end of the run will penetrate the house's stucco exterior, I'd rather keep any movement away from that interface.

And I really do believe the wall and house move in their own ways depending on groundwater conditions, so that's my other hesitation with too much rigidity.

quotw; I'd rather keep any movement away from that interface.
You show an anchor on the building's wall, so that would "interrupt" any movement at the wall's penetration. You are being paranoid about the expansion.

I drew one, but I plan on a total of four to support the 20' of pipe -- two on the house, two on the retaining wall. Though I suppose I can cinch down the ones on the house, and leave the ones on the wall slightly loose.

I've run long runs of copper for refrigeration systems - never had an expansion problem.

Why would you use copper for a drain line? PVC painted a light color would block the UV.

Mainly aesthetics. The portion along the retaining wall is running just above a flower bed, so I picked copper for appearance. The rest of the house is copper DWV, so it was easiest to keep it copper for that first half, too.

Paint the PVC an attractive color to blend in with the retaining wall.