Plans have to be carefully drawn by an engineer. “The most dangerous point is when you have the whole basement dug out, and it is supported on dirt,” says builder David Perez. If it rains, the house can collapse, taking a neighbor’s home with it.
The process is also expensive and time consuming – one Washington, D.C. excavation contractor estimates that a 700-square-foot basement excavated three feet down and carefully supported would cost about $44,000 before any finish work is done. But some home owners say it is worthwhile, because there simply isn’t any other way to increase the size of their homes.
Source: The Washington Post, Elizabeth Festa