Copper throughout the entire house means that there will probably mean no major plumbing work to do. Also whenever remodeling is done copper is installed.
I know that's off topic from what you were originally asking about but I thought it is good to make a note of this just in case you ever run in to this while checking those pipes.
top quality copper will last 50+ years if not subject to electrolysis, but it's more vulnerable to settlement and earthquake, exposes users to minute amounts of lead, and copper. PEX is hard and flexible, I don't know if history shows any problems from rodent attacks? Being a chemical based product, it exposes users to some amount of chemicals which many may prefer to avoid. PEX is faster to install, only approved for use in San Francisco about a year ago per my plumber source who uses it.
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For a variety of reasons, San Francisco code doesn't allow plastic: for supply, copper is required. I've seen two houses in San Francisco where someone saved a buck by hiring someone who didn't know the local codes, and all the plumbing had to be ripped out and done again. The domino effect of the fallout was severe, for the plumbers, generals, and homeowners. Just make sure your contractor knows the SF codes and has the plumbers who have real experience with copper.
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