What happens if work was done at my house without a permit?

There are a few things that will happen. The work may be required to be exposed for code compliance. This includes the footings, framing, electrical, plumbing, hvac and insulation. Or you may be required to submit letters from licensed mechanical contractors certifying the work was done in compliance with the current code (does not include Footings). The contractors will also be required to obtain mechanical permits for the work.