Filing repairs for rental property

[Daniel Rines]

I'm hoping someone can give me some insight to this rather individualized question.  I own a 2 story duplex and rent the 1st floor and live on the second floor.  In 2017 I built a laundry room with hook-ups for both my washer/dryer and my tenants washer/dryer.  Expenses included: plumbing, duct work, electrical, and lumber.  I'm looking back at the expenses for this and not sure how to sort them out since we both use the room.  My best guess was to split the cost in half and itemize that way since we share the room but I honestly have no idea.  Any help would be much appreciated.  Thank you in advance!

-Dan