Zimmerman is a surname variant of the German Zimmermann, meaning "carpenter" (literally "room man").
The modern German terms for carpenter are Zimmerer, Tischler, or Schreiner, but Zimmermann is still used.
Zimmer in literal German means "room" or archaically a chamber within a structure; it is cognate with the English word "timber".
The German mann means "man" or "worker".
Later generations also altered their original family names frequently after being in the United States many years.