Venting a new drain

[rice9923]

Adding a new drain which consists of two sinks in my basement.
Do not have access to the existing vent system. I must run a new
vent to the outside of my house for this system.
QUESTION: What is the mininum diameter pipe that can be used for this vent?

thanks,

 

[hj]

pipe

1 1/2" in most cases.