Interior design addresses the functional, spatial, and technical aspects of interior environments: space planning, furniture layout, lighting design coordinated with electrical rough-in, material specification integrated with construction dimensions, finish schedules as construction documents, and building code compliance. Interior decoration is the aesthetic layer — selecting colors, furnishings, and accessories for completed spaces. On a construction project, interior design belongs in the pre-construction process because design decisions affect construction. Tile selection affects drain rough-in elevation. Cabinet layout determines blocking locations. Lighting design determines electrical rough-in positions. These are construction decisions expressed as design choices, and they must be made before the construction phases they affect — not after the work is built.