The antonyms for the word 'underbuilding' are numerous. The most apparent antonym is "overbuilding," which implies construction beyond what is needed. "Excessive building" is another term that refers to too much construction. "Overdevelopment" is a term that describes the creation of too many houses or businesses in a specific area. In addition, "overpopulation" occurs when there are too many people in a region, causing overcrowding and housing shortages. Finally, "underpopulation" is an antonym that refers to a region with a lower population density than expected. Thus, these antonyms describe different scenarios of construction and occupancy, highlighting the importance of balance when developing any place.