If you plan to turn your basement addition into a comfortable living area, some form of ventilation becomes a must in order to control the air quality.
Dampness is always an issue for this type of home renovation, but there are ways to keep it under control. If a forced-air heating system is already available, the basement area can be added to it.
Otherwise, you can opt for reversing-fan technologies, air-exchangers, or even dehumidifiers–with the downside being that those would have to be emptied periodically.