Belly Board and Z-Bar... racehorses or rock band?
Updated: Sep 22, 2019
Sorry, not that much fun! Belly board is used as trim at the bottom of siding and Z-bar is the flashing above it. In the photo above the bottom portion of T-111 siding has been cut away and a belly board flashed with Z-bar above has been added.
Often the Z-bar flashing is not sloped away from the house which means water pools near the siding and the flashing will deteriorate sooner. Steel Z-bar can be expected to last about 15 years, even if painted.
If a starter strip is not used on the bottom course of lap siding then it will not flare away from the house and shed water adequately.
This Habitat for Humanity guide has lots of siding tips: find Belly Board section about half way through.
Buckling siding usually means it has been nailed improperly or that an 1/8 inch gap has not been left at the butt ends where the boards meet the trim for expansion and contraction. This may be remedied by pin backs as described in the following publication. (There should be no gaps between boards.)