You have to meet Commercial code, ADA units, fire sprinklers, elevators (maybe), walkways, exterior stairways, etc.

We asked the building inspector to allow/accept the existing non-compliant but pretty good back stairway as an existing condition.

Stairway railings, especially bannisters around the tops access area of the staircase, wrapping of the house to help waterproof it may never have happened, window sizes for fire exit, etc.. may all be off so if you plan to rent the house, consider the cost to make it safe for the tenants.  

It could also be an old stairway where the steps themselves flex too much.

According to COH, this conversion process would also trigger a general life-safety inspection, and potentially the need to bring the entire building up to 2024 code (at least in terms of safety issues: electrical, stairway tread width, etc.) 

As we are seeing from many groups now, distributions are being paused, not because of debt issues or current cash flow issues, but rather, when you underwrite your capex budget for 5 years, and now have to hold likely 3 more years, all those deferred maintenance items that didn't come up in the first 5 years are now needing addressed: think repaints, roofs, foundation, exterior stairways, etc.  

Since the stairway is dark wood, I am thinking to put dark hardwood on the lower level.

@Matthew Olszak - there is a stairway from the back deck of the first floor apt, down to the basement stairs, so there would be some protection from the elements.

I put in a few wireless light switches because despite the previous renovators going cray cray with the outlets and electrical wiring, they didn't bother making 3 way switches where a few three way switches would have made sense, like the stairways.

All you're doing is paying for all that negative CF upfront.Third, think of a stairway in a house.