Basement

Basements are underground floors that can be built underneath some buildings in The Sims 2 and The Sims 3. Basements were originally created using the foundation tool, and were sometimes difficult to create until a patch was released for The Sims 3, which added the Basement tool into Build Mode; this tool was also included in The Sims 3: World Adventures, and can be used to create tombs.

Basements are not possible in The Sims as foundations are not available in the game. Basements in The Sims 2 and un-patched versions of The Sims 3 base game are created by placing an area of foundation that is hollow in the center, then lowering the terrain inside the hollowed-out foundation so that the area in the basement is the equal height of a typical floor, thus making the basement a fully usable space accessible by Sims (assuming that the Sims have a means to reach the basement, such as by stairs or elevator). Pre-existing buildings that do not rest on a foundation can not have basements added to them, though basements can be added to pre-existing buildings that do rest on foundations.

The Sims 3 versions 1.5 or later include a basement tool in Build Mode. The basement tool can only be used on buildings that are not built on a foundation. The basement tool does not create basements for buildings on foundations; those basements must still be created in the same manner as they are created in The Sims 2. Basements created using the basement tool may go as deep as four stories below ground level.