Building Expansion is a term used to describe the process of increasing the size of an existing building. This can be done by adding additional floors, rooms, or other features. The term is often abbreviated as ELL, which stands for 'extension, loft, and/or level'. Building Expansion is a common practice in many industries, such as construction, architecture, and engineering. It is a cost-effective way to increase the size of a building without having to start from scratch.