Loan question - Residential vs. Commercial

[Calvin Kwan]

Hi, 

I am targeting 4plexes in the SF Bay area for purchase in the coming months.  Up to 4 units I understand I can use a conventional primary resident loan, but above 4 units it requires a commercial loan.

If I were to buy a 4plex with a conventional 30yr loan, add an ADU, would I still be able to refi with a conventional residental loan? With the ADU be considered a 5th unit, pushing me to require a commercial loan?

Thanks,
Calvin