If you want a friend to move in to your rental unit, it’s a good idea to check with your landlord first. For one thing, your lease or rental agreement may require landlord approval to bring in a new roommate (even if the new person is simply replacing another tenant who is moving out). And if it’s a matter of adding a new roommate to your current group, be sure to check whether your lease or rental agreement limits the number of occupants. If you violate a lease clause that restricts the number of occupants or requires landlord approval of new roommates, your tenancy may be at stake if your landlord finds out and is unhappy with what you did.
Even if your landlord is not in the area and never stops by (or is not likely to care if a new roommate moves in), it’s a good idea to ask the landlord’s consent. The landlord will probably figure out what’s going on before long, and the landlord may resent your sneakiness more then he or she resents your roommate.
Use this Sample Letter Requesting Landlord Permission to Add a Roommate when you want a new person to move into your rental.
For more on the subject, see the Nolo article Adding a New Roommate. Keep in mind that if you’re a tenant in New York, you have different rights than most tenants under New York’s “Unlawful Restrictions on Occupancy Law,” commonly known as New York’s Roommate Law.