“Parts that together form an entire structure, such as a building. The term includes those parts of a building such as walls, partitions, floors, and ceilings, as well as any permanent coverings such as paneling or tiling, windows and doors, and all components of a central air condi- tioning or heating system including motors, compressors, pipes, and ducts. It also includes plumbing fixtures such as sinks, bathtubs, electrical wiring and lighting fixtures, and other parts that form the structure.” Pub. 946, How to Depreciate Property (2020), IRS.