Loans for houses with detached guest/carriage house

[Suzanne B.]

I live in an historic area where many houses have detached carriage homes that people use as rentals.  I am curious to know:  A) are there any loans specific to situations like this (single family residential, but with on-site rental unit), and B) is it possible to use the potential future rental income as income qualification on the loan?  That latter question may depend on if the current owner is or ever has rented it out.