Master Bathroom Renovation and Detached Accessory Dwelling Unit (ADU)
Project Details
This project encompasses the structural design and architectural planning for a residential renovation and the construction of a new detached Accessory Dwelling Unit (ADU). The renovation portion involves a 200-square-foot master bathroom addition featuring a steam shower, walk-in closets, and skylights. The new detached ADU is a self-contained living space approximately 33′-1″ x 18′-2″ in footprint, designed with a vaulted ceiling over the common living, dining, and kitchen areas, alongside a separate bedroom and bathroom with 8-foot flat ceilings. The structural engineering for the assembly utilizes Douglas Fir Larch lumber (No. 1 for beams and No. 2 for joists and rafters) and structural plywood sheathing. The foundation system is composed of reinforced concrete stem walls and independent footings, including specialized pedestals (PF1 and PF2) designed to support a soil bearing capacity of 2,500 psf. All concrete work was specified with a minimum compressive strength of 2,500 psi at 28 days. The design adheres to rigorous safety standards, including the 2025 California Building Code (CBC), 2025 California Residential Code (CRC), IBC 2024, and ASCE 7-22. To ensure stability in a high-seismic region (Seismic Design Category E), the structure employs wood shear walls with a response modification coefficient (R) of 6.5 and integrated Simpson Strong-Wall systems. The building is also engineered to withstand wind speeds of 92 MPH under Exposure B conditions. Comprehensive fastening schedules and moisture control measures, such as pressure-treated lumber for all elements in contact with the ground or exposed to weather, were integrated to ensure long-term durability.
Role
Structural Engineer/Designer
Services Provided
The scope of services included the preparation of structural analysis, structural calculations, and structural plans for the proposed detached ADU and attached master bathroom addition. The structural analysis considered wind, seismic, dead, and live loads in accordance with the California Building Code (CBC) and applicable local amendments. The work included the analysis and design of the detached ADU structural system, including foundations, floor framing, roof framing, shear walls, beams, columns, and structural connections. For the attached addition, the services included a structural review of the existing residence framing within the area of work, the analysis and design of the new foundations, bearing walls, beams, headers, and roof framing modifications, and verification of load transfer into the existing structure. The services also included the preparation of structural drawings consisting of the foundation plans, floor and roof framing plans, shear wall layout plan, structural sections, connection details for tying the addition to the existing structure, and typical structural details, notes, and specifications to support permit review and construction.