Residence into STR depreciation and cost segregation

If I turn my personal residence I have owner for 9 years into a STR, what value do I use for depreciation of the property?

Can I also do a cost segregation based on that value?

I have several LTRs but not any STRs as of yet. I have a W2 for the next 2 years. I am looking to take the STR depreciation against my W2 wages.