What is the defining feature of exterior door frames compared to interior door frames?

The defining feature of exterior door frames that distinguishes them from interior door frames is the presence of a sill. A sill serves as a crucial component in exterior door frames, providing a surface that helps to direct water away from the door and prevent water intrusion into the building. This is especially important for exterior doors, which are exposed to the elements and need additional protection against weather conditions.

In contrast, interior door frames typically do not require a sill because they are located within the protected environment of the building. Therefore, the design of exterior door frames incorporates this feature to enhance their functionality and durability against weather-related challenges.