Walls in buildings are constructed of various types and materials. They may be organized as exterior vs interior, or as load bearing vs non-load bearing, or as prefabricated vs built-in-place. Any walls which are classified as load bearing means that they carry vertical (downward) floor loads, as well as lateral loads. Walls are typically planar, but they may also be designed with flanges, or as a closed cell assembly such as the elevator core of a tall building. Exterior walls may be load bearing, or they may only be required to act as a protective environmental shield. If acting as shields, such walls are known as “envelopes” or non load bearing “curtain walls”. Even if a wall is a curtain wall, it must carry its own vertical self weight safely and it must be able to transfer lateral wind loads to the building support structure. These cladding structures have tributary areas, part of which transfers loads to other building elements and eventually these loads move down to the ground. A common and economical way of transferring lateral load down to the ground is via shear walls.