Primary Residence - What is the legal definition?

[Susan Elliott]

I'm learning about mortgage options for my first investment property. This is also my first home purchase, so the FHA loans and other owner-occupancy options are on the table. I currently live rent-free as a caretaker just 15 miles away from the duplex I'd like to purchase. I don't necessarily want to move.

My question is what is the legal definition of "primary residence"? Could I rent out both sides of the duplex but still call it my primary residence by changing my address to that of one side of the duplex? Could I rent one side 100% and the other 50% (6-month lease or short-term AirBNB perhaps) such that it is my primary residence? 

From what I have researched, I may have more loan options if it is a primary residence. However, I do want this to be a long-term investment property. Thus, I wonder if starting an LLC and getting a traditional 20% down loan may be the best long-term option for this property while providing me the flexibility to NOT live on the property.

Any other creative ideas for conventional financing out there? (I am only beginning to learn about private lending currently).

Thank you all!