10 years ago we renovated  a 150 year old home.   It had rather good windows and siding.    $18,000 won't do much.  You need a new kitchen.  If you want it for the employee it is also for his:  wife or girl friend.  Happy wife means happy employee.   New kitchen = new wiring, new plumbing and new insulation.    I'm guessing it has wallpaper.   There is new paint.   Old flooring/carpet....  now new flooring.   If you need new windows or doors  keep adding $$$$.  

I'd only do it for an employee.   Being a landlord is a pain.   My tenant house is across the front yard.   I see what is going on.   Even living next door doesn't shame them into staying current on bills.   Part of the problem is I refuse to put the power or propane in their names.   I'd rather get stuck with the LP or electric bill than have to clean up frozen and broken pipes.  

We gutted most of the downstairs to the studs,  new wiring,  new insulation,  new plumbing, totally redid the kitchen and one bathroom.   That was about $75,000.   Lots of other stuff has been done and still needs done.   $100,000+ will have been put into this house in the past 10 years.