Health drain for walls?

[Berwin]

Hi

I need to add a health drain on my walls. 

I have removed hammering from walls and wall piece adds 200 health. 

I have caused the wall 'stump' to be removed when it's created because it seems to be immune to damage (unless this can be fixed also) and can't be hammered (immunity).

When the first wall section is place it is showing as half wall, then the second piece reduces it's height, but is fine after that.  Can the first piece show 1/4 height?

Main request: I would like to add a health drain to the walls.