Thanks for the quick replies.
Yes- the work was done on my side of the boundary and I paid for all the work, which was invoiced to me.
I was replacing about a 20 ft section where the wall was failing. My neighbor wanted to increase the scope of the work to add an additional section of new wall so he could add more backfill to his section. The sharing of costs was not easy to estimate since it was just one big job, but we agreed to split most of the costs 1/3 - 2/3. This wall is about 6 ft high, so also serves as a boundary fence and has benefit to me also.
I ended up paying all the design and engineering costs myself.
I can't find anywhere in the forums or tax code that really covers depreciating a capital expense, where I received some contribution. My neighbor won't depreciate this because his is not a rental property.
