Seattle-based FabCab offers several ADU models ranging in size from 300 to 1,800 square feet. FabCab units are precut timber-frame structures. All components are sent to a building site as a kit, which includes the frame members, wall panels, doors, windows, siding, trim and fixtures. The kit must be assembled at the site by a licensed contractor. (FabCab offers a list of qualified contractors in Washington state and some areas of New England; a nationwide list is in the works.)
Universal design features include a step-free entry, wide doorways, no hallways, a walk-in shower with trench drain, varying height of countertops with recessed knee space under the kitchen sink, lever door handles and plenty of natural light.
Costs for a FabCab are estimated by the company to start at $155 per square foot. A 550-square-foot unit can be assembled in about two days, according to the manufacturer. This time frame does not include preparing and installing a foundation for the structure or obtaining building permits and other requirements for occupancy.