There is a recent requirement in all Towns today for the presence of an emergency egress window(s) in the basement if there are some types of a finished room. This is typically a window in the basement that is large enough for a person the exit the basement and then climb up the ground outside. Requirements for this are complex. Should the basement be used for full time habitation, the need for this is very likely. To be aware of the exact requirements contact the Town the house is located in for your exact local requirement. Construction of one egress window will cost between $5000 and $10,000. Some basements may require more than one.
The construction of an egress window is a structural change to the house, and will require a permit from the Town, and a Certificate of Occupancy, with some approval to the plan by a Professional Engineer.