Since you can depreciate diff components if cost-segregation study is done, can you split a building's basis into commercial vs residential, based on respective sq footages, and depreciate part of it over 27.5 years and the other part over 39 years?  I read things about if 80% or more is residential rental, I may be able to take entire building over 39 years.  Not sure if it's less than 80% if you can split into 2 segments 27.5 and 39 yr properties.