What is a cupola typically used for on a building?

A cupola is primarily used as a special vent. It serves as an architectural feature that allows for ventilation in a building, particularly in attics or large spaces. By providing an outlet for hot air to escape, a cupola helps to regulate temperature and maintain air circulation, which is especially valuable in structures with significant thermal load or where humidity management is essential.

While cupolas can also enhance the aesthetic appeal of a building, their primary functional role in ventilation sets them apart. They can contribute to the overall visual character of a structure but are designed fundamentally to manage airflow. Other options, like adding structural support or improving lighting, are not main purposes of a cupola, which highlights why the focus on ventilation makes the correct answer stand out.