The execution needs to be spot on, otherwise you will have a hard time selling the 2 halfs and might have to discount them to the point where you loose money.The property you are looking at does not have enough square footage - you want them to be at least 1200 Sf, better 1400 per unit.

@Kevin MelsonIt can be used, but they don't give you the option to implement a detailed rent roll, where you can enter the rent/square footage/layout per unit.

There is also the opportunity to enclose a back portion of a carport that has easy entrance to the house that will add sq footage in the future (my hubs is in construction so we do a lot of the work ourselves or have access to subs at a discount).

We are charging the tenants for water damage repair and refinishing floor square footage that was damaged by them.

Bathroom and kitchen are going to depend on quality of material you are installing, square footage, and labor. 

I understand that I have to make adjustments to comparable houses for an extra bedroom or bathroom for example and I understand the math, but how do I determine what a bedroom, bathroom or extra square footage is worth?

Maybe I'm way overthinking this and it's as simple as finding the same style home with same bedrooms/bathrooms and figuring out the square footage. 

So from what i understand in Philadelphia, the approvals are considered on the lot square footages.

@Julien Weinrott Hey Julien, it sounds like you are possibly mixing the zoning ordinance with ADU laws, but yea, like Will said I would be interested in knowing what you are looking to do with it and what's there now (existing square footage and all) to get a better idea of what the options are. 

The square footage, location and the year of the construction is needed too.Appreciate it.