Thanks for the link. I am not sure what asbestos millboard is, would hardie board be equivalent?
I wonder if putting metal studs (to act as the non-combustible spacer) against the back wall. then the hardie board with a 2" space at the bottom might work as the barrier. What's there now is just a thin sheet of metal and it only covers a very small area, I definitely want to rectify that.
[Edit]
I also definitely need to pull it back from the wall, maybe 18" from the new wall I build. I would also consider doing the same along the length of the ceiling where the pipe is, seems to be cement board there now. but no spacer.
