When is a STR/MTR by the ROOM then make your resident an investment property?

[Lisa W.]

I know Primary Resident is when you actually live in the unit for majority of the time.

Q: If I rent out a room in my primary resident, is there a percentage (i.e. 2 rooms rented out of 3 or sqft, etc) that then makes the primary residence qualify as an investment property?  

Or, is it a dead fast rule that if you're living in it then it's a primary residence (period).  

Thank you!