How much cash reserve should I have per rental?

[Erik Howard]

Hello, 

I'm brand new to bigger pockets. So this question question has most likely been answered already. But here goes! 

My wife and I are considering buying a duplex. Built in 2004. We plan to use an FHA loan and 3.5% down. We hope to be able to buy a new duplex every year or two. We will put each duplex on 15 year mortgages. If we are able to continue buying properties we could end up with 10-15 duplexes in the next 15 years. But with that many houses there are bound to be tons of things that need fixed and repaired. Like a roof, floor, drywall, general cleaning and rehabbing every time a tenant moves out. So here's the question.

With all the potential repairs, how much cash should I have available for repairs per duplex?