Which type of stairs serves all apartments within a building?

The type of stairs that serves all apartments within a building is commonly referred to as common stairs. These stairs provide access from the ground floor to upper levels, allowing residents to reach their individual apartments. They are a characteristic feature of multifamily residential buildings, ensuring that all units have a shared means of vertical circulation. Common stairs can also be designed to meet building codes and safety standards, facilitating efficient evacuation during emergencies.

Wing stairs typically serve only specific sections or wings of a building rather than accessing all apartments. Single stairs might imply a simplified design or limited access, which would not accommodate a multifamily setting. External stairs, while they can provide access to upper floors, generally serve as an alternative or supplementary means of egress rather than the primary access to all apartments in a building.