"can the $50K be completely expensed."

Here's how I teach this:

A broken window is repaired, even if by replacement = directly deductible. A repair Expense.

All the windows are replaced with hurricane resistant = capitalized and depreciated. An improvement that is a renovation or remodel activity. It's an expenditure that is an investment in the property for its future (this wording helps clients understand it).

New walls and other structural work and system changes (new sewer line) would never be expense. And any engineering or architectural costs for a renovation, permits, would be part of capitalization. New deck? Capitalize. Fix some stairs? Expense. Replace the stairs, needing building permit? Capitalize.

In a rental, you go through some segregation, too. New appliances is not the same as a new garage door.