Isn't all copper the same?

not all copper is created equal.

Copper wire is the purest because it needs to conduct electricity at maximum efficiency.
Copper pipe is not as pure, because pure copper pipe would be too soft, and it needs to maintain structural integrity.

Now, sheet copper for roofing or otherwise isnt load bearing, nor does it conduct. it is typically decorative, so they use low grade copper, AND the fact that it is so thin makes it surface area to weight ratio less than desirable for smelting. It has a lower recovery rate and gets downgraded.

I put all my sheet copper in a separate bin. it comes from the strangest places sometimes, but i know better than to mix it with my number two or number one.