Very peculiar tax situation (short-term rental depreciation?)

[Ricky Stafford]

I rent out roughly 40% of my house on Airbnb (it's divided by door, has its own open kitchen living area, bathroom, bedroom). I renovated and started renting the middle of last year. 

The apartment isn't used for personal use at all, so I assume I'm able to claim depreciation even if it's vacant. It rents consistently, about 20 days a month, but there are still some vacancies. I've already filled in tax info for the 5 yr depreciating items that I bought last year for the apartment. 

My question is, can I claim residential depreciation over 27.5 years for the apartment itself since it was a personal "home" that was converted to a rental? Would I just take the FMV of the entire house and multiply by 40% / 27.5 for yearly depreciation? And how would I find FMV in the first place?

Thanks in advance for any insight.