Yes, it is possible to add a basement to an existing house in some areas.

There are many places where it is not possible to dig out a space beneath a house because of the elevation or the composition of the soil. Coastal areas often cannot have a basement, because there is no place to dig. Marshy areas are subject to the same water and dampness problems.

The type of foundation the house is built on will also affect the ability to affordably add a basement to an existing home.

This is definitely not a job for the average do-it-yourselfer. Mistakes can damage the entire foundation and structural integrity of the house.

If the underlying ground is stable and the house is properly supported during the excavation process, a basement can be enlarged or added to an existing home.