What is the term for changes made to the basic design or plan of a building, often to correct deficiencies?

The correct term for changes made to the basic design or plan of a building, particularly to address deficiencies, is "remodeling." Remodeling involves a significant alteration of a structure's layout or configuration and often includes updates or improvements to both aesthetics and functionality. This process typically aims to enhance the usability of a space and may involve changing room layouts, adding new features, or improving existing ones.

Rehabilitation usually refers to restoring a building to a good condition while preserving its historic elements, while modification can imply smaller adjustments rather than substantial changes. Restoration is associated with returning a property to its original state, which does not necessarily involve correcting deficiencies but instead aims to maintain historical accuracy. Each of these terms has its unique connotations and focuses, making "remodeling" the precise choice for changes aimed specifically at improving a building's design and functionality.