If you are adding 1,000 sqft you will have to expand the foundation, expand the roof - that's about 200k-250k.

This house is also renovated and roof, water heater and appliances are pretty new.

Luckily I didn’t have to do a new roof. 

As I understand it, anything built pre-Katrina that survived had a new roof put on about 20 years ago, but from Google street view it looks like a lot of them are metal. 

You still will need to change the hvac, water heater, and roof periodically along with other breakdowns. 

It was a duplex that required full rehab (roof, siding, new retaining wall...cosmetic rehab upstairs with HVAC, kitchen, bath & deck...downstairs got cosmetics with new kitchen & bath with mini-splits for HVAC)3.

Roof in good shape, 80% of floors in great shape. 

And while, generally speaking, there is not much practical gap between 27.5 and 39-yr depreciation schedules for a small property, the distinction is nevertheless significant due to the special rules afforded to non-residential properties, such as expensing of roofs and HVAC.Yes, there's this concept that the property's character is determined at the building level.

You will also not have the luxury of spreading major CAPEX expenses and some maintenance expenses across all units (one roof, one electrical system, one lawn, one parking lot, one HVAC system, etc)- When you buy the portfolio, there is a pretty good chance that at some point you will want to sell off the lower-performing assets in the portfolio or the assets that cause a headache.

The first floor needs some updating but the upstairs needs to be gutted because they had a roof leak years ago.