The accessory dwelling unit prototype was prefabricated, then installed in the rear yard of an existing single family house in Tucson to be used as a home office/ guest room. We have developed separate units for bathroom/ kitchen and living/ sleeping that can be added as needed to comprise a complete dwelling. Structural insulated panels form the floor, walls and roof, lower construction time and providing excellent acoustic and thermal insulation. This model allows for social, economic and environmental alternatives to residential development.