Will adding a second bedroom reduce turnover?

[Gregg Reinbold]

I have 5 unit apartment building. One unit is a 2 br/ 1.5 ba and the remaining  4 are 1br / 1 ba.  I cannot seem to keep a tenant in the 1br /1ba for longer than a year, but I have the same tenants in the 2 bedroom for the last four years.  

I am considering adding a second bedroom to 3 of the 1 bedroom apartments thinking it would lower the turn over rate.  I estimate that I would lose some monthly cash flow from what it would cost to build the units compared to what I could rent them for but that I would gain in the end if I can lower my vacancy rate. 

Anything thoughts?