that I filled in with dirt. Biggest regret of the project was not digging it out and making a basement space under the addition. Was doing it on the cheap at the time.

Fast forward 13 years.

Am thinking I want to add a second level addition to the 13 yr old addition, AND dig out the basement and make that a rec room.

Is there a way for me to keep the current foundation, or some iteration of it? Can I dig deeper and shore up the existing foundation and just use that, to create the basement space I should have built originally?

Or do I need to tear down the whole thing, including foundation, and start over.

In either case, I am planning to tear down and rebuild the original addition (so digging out from underneath the crawl space isn’t the way I would do it).

It's a 25X20 addition that would be now 2 levels above grade and a basement underneath...