Current Tenant want to add a roommate

[Veronika Pachunuri]

Hi - a new landlord here and need some advice. I just rented out a single-family home to two last year in college students ( they are a boyfriend and girlfriend). They did not have a good credit score, but they have a solid co-signer, one of the tenant's parents. It has been a month since they moved, and they asked if they could add a roommate. Should I treat a new roommate as a new tenant and ask for 3x of the monthly rental payment or evaluate a tenant based on their part of the monthly payment (I do not know how they would split the rent among themselves). My requirement is 3x monthly rent and must be paid in one payment each month. I planned to send a pre-qualification letter asking if the person can pay 3x monthly rent payment and additional questions. Please advise how to qualify for a new roommate.

[Veronika Pachunuri]

Quote from @Richard F.:

Quote from @Veronika Pachunuri:

@Kevin Sobilo, Thank you, this is great information and precisely what I was looking for. I will do a pre-qualification questionnaire and application and run a background check. Then we need to add a new roommate to a lease agreement. 

 Aloha,

You still should also perform a credit check on the new person, and verify whatever income they do have. No use asking for problems if they have issues. However as @Kevin Sobilo states, regardless of the group makeup, the total household income needs to meet your requirement, not each individual. Typically with students, I also get a Parent from each student as cosigner, and also run their credit. Usually they can provide a sizeable savings statement as well.

Now, to add the new Tenant...you are going to use a simple one page addendum to do so, right? One that all of the adults would sign, agreeing this person will also be a Tenant, and referencing the original date, the premises, and the name of the Agreement that it will become an addendum to.

Thank you so much for clarifying! The original two roommates are a couple. And the boyfriend's mom is a guarantor on the lease, and she makes 3x the rent. Two roommates also make 3x the rent, but their credit score was not enough to qualify, so we added a guarantor to the lease. 
I thought I needed to do the lease all over for all three tenants. I only need to do a one-page "Change in Terms of Lease Addendum," which all 3 tenants will sign. 

My original transaction was done by an agent who found the roommates and did all the paperwork, screenings, etc. So I am learning how to do it myself. I am using RentRedi. It is helpful!