Dipped Floor on First Floor of 2 Family home

[Mahran Izoli]

Hi All, 

I just purchased a 2 family home in Providence, RI. Currently, the first floor has a some pretty substantial dips in it. I'm not sure if its the sub floor or the joists underneath. 

My question is: Should I go through the repair prior to renting the unit? Or should I wait until I have more cash saved to repair down the line. I don't want to risk spending too much time on it losing out on potential rental income. The unit is in decent shape and definitely livable. I've attached some photos. Would love to hear some opinions on what actions you all would take if in a similar situation.