Specialized Prefab Manufactured Home & ADU Builders in Southern California. US Modular Inc. is very unique in the construction industry as we are a second-generation full-service general contracting firm, developer, and licensed manufactured home retail dealer specializing in prefabricated home construction. We build accessory dwelling units (ADUs) and single-family manufactured homes that follow the local building codes and HUD guidelines. Our manufactured homes are also eligible for the MH Advantage program by Fannie Mae.