As the signer of a rent stabilized lease, a primary tenant has a right to renew the lease at the lease expiration date, subject to rent adjustments regulated by the Rent Guidelines Board and the Rent Stabilization Code.
Once the tenant on the lease moves out, the landlord is not required to accept a remaining occupant as a new tenant unless that occupant has succession rights. If the roommate is accepted as the new tenant, the landlord may charge a vacancy allowance.
If the apartment is not rent regulated, you are free to renegotiate with the landlord to have a new lease naming you as the sole tenant. However, so can your co-tenant. The owner is not under any obligation to renew your lease, rent it solely to you, or to renew it with the same names unless the current lease specifically states so.
If the apartment is rent stabilized, the primary tenants named on the lease both have the right of renewal. If you wish to have a new lease naming you only, you should get the co-tenant's consent (in writing). The owner may not pick sides and renew to only one of the current named tenants without consent of the other.
If you renew and a new roommate signs the lease, the landlord can charge a vacancy allowance. This is considered a "new" lease and is subject to the vacancy allowance rules. However, if you renew the lease on your own (no roommate signs the lease), the landlord cannot charge the vacancy allowance. Under this scenario you can still have a roommate (where only one tenant is named on the lease, state law allows you to have one roommate without the landlord's consent), and the roommate would not trigger a vacancy increase. More information on roommates can be found in an HCR FAQ.
The presence or absence of a guarantor would not trigger a new lease. Note that renewal leases must be offered on the same terms and conditions as the expiring lease. Therefore, if no guarantor was on your first lease, the landlord may not impose this requirement on subsequent leases.
Finally, if you are married, the landlord must put your spouse on the lease if he/she is requested to do so and cannot charge the vacancy allowance. However, if you ask the landlord to put your fiancée on the lease before you are married, he/she could charge the allowance.
If the lease had expired when you returned, and the apartment is not rent stabilized, you have no right to a lease or to return to the apartment. If the apartment is rent stabilized you may have had the right to a lease renewal. However, if you failed to respond to a properly served lease renewal offer, you may have to file a complaint with NYS Homes and Community Renewal (HCR), the state agency which administers the rent laws. You will have to show that you have a good excuse for not having returned a properly tendered renewal offer. The matter may also end up in Housing Court if the landlord attempts to prevent you from occupying the apartment.
A signed lease which is still in effect (i.e., not expired) is proof that you have the right to occupy the apartment. If this is the case and you would like to return to the apartment you should talk to the landlord and let him/her know that you may have to call the police if he/she does not let you return. If this doesn't work you may have to file an action in New York City Housing Court to regain access to the apartment. For more information on housing court in New York City, see our Legal Assistance page.
If only your son stays as the only tenant and signs up for a new term, it is considered a renewal lease. However, if s/he asks the landlord to add another name to the lease the landlord can charge the vacancy allowance and it becomes a vacancy lease. In this situation, the landlord could raise the rent for the apartment by the vacancy allowance.
Your son can renew the lease and take on one "roommate" (someone who is not on the lease) without an additional charge. State law allows your son to have one roommate and s/he need not ask the landlord's permission. The roommate is not a subtenant, just a roommate. More information on roommates can be found in an HCR FAQ.
Whoever the current primary tenant is could also apply to the landlord for a lease assignment assigning the lease to you. A lease assignment conveys to another person all the tenant's rights to occupy the apartment, whereas a sublet is based upon a temporary absence by the prime tenant who intends to return to the apartment at the end of the sublease. This is unlikely to result in your avoiding the full vacancy increase because a landlord may take a vacancy allowance when a lease is assigned.
Also, a tenant may not assign his/her lease without the written consent of the owner, which may be unconditionally withheld without cause. However, an owner who unreasonably refuses to grant permission to assign the lease must release the tenant from the lease upon request of the tenant upon 30 days’ notice. If the owner reasonably withholds consent, the lease may not be assigned and the tenant will not be released from the lease.
So, be careful, the primary tenant could end up being released early from the lease and the owner may still not consent to assign the lease to you.
First, you do not say if the apartment is rent stabilized or not. If you are not sure, contact NYS Homes and Community Renewal (HCR), and they will tell you. If the unit is stabilized, there are specific situations in which a landlord may increase rent. More information on roommates can be found in an HCR FAQ.
The NYS Attorney General's Office website also discusses roommate, in all types of housing, in the Apartment Sharing section of their Tenant's Rights Guide.