Adding a partially finished basement to listing square footage?

[Ryan Biankowski]

I am in the middle of a rehab right now near Mayfair where there's about 300 sq ft of partially finished basement.  In this section it has flooring throughout, wood paneling for 2 walls (painted cinder block for 2 walls), lighting and electrical, a old (functional) large heater and a finished older bar area.  I had to remove the old drop ceiling due to beams being added so there is NO actual finished ceiling now.  Does anyone know the rules on this and when it can be added as square footage when we sell the house?  300 sq ft will go a long long way in my area.  Realtor seems to think it's OK to be added.