Structural Analysis & Design for a Proposed ADU
Project Details
This project involves the comprehensive structural analysis and engineering of a proposed Accessory Dwelling Unit (ADU) with a footprint of approximately 39.2′ x 13′ and a mean building height of 17.26′. The scope of work required modern engineering solutions for a complex multi-material assembly, including a primary structural frame utilizing HSS steel columns (3×3×1/4), HSS floor beams (5×3×1/4), and high-strength Douglas Fir-Larch timber columns (up to 8×8). The building envelope is engineered with cold-formed steel studs at 16″ O.C. for exterior walls and light-gauge steel joists for the roof and floor systems, integrated with EPS foam insulation and plywood sheathing. The design process utilized rigorous structural analysis through finite element modeling to evaluate the building’s performance under various load combinations, including dead, live, wind, and seismic forces. All structural components were engineered in strict accordance with the 2019 California Building Code (CBC), IBC 2015/2018, ASCE 7-16, and ACI 318-14 provisions. Significant engineering attention was directed toward lateral load resistance, ensuring the ADU can withstand environmental stresses in a high-seismic region. The structure is designed for Seismic Design Category D and wind speeds of 96 MPH (Exposure Category B), utilizing a lateral system of light-framed walls sheathed with wood panels. The foundation system features multiple independent reinforced concrete pad footings and piers (F1 through F6) designed to perform reliably under a gross allowable soil bearing capacity of 2,000 psf.
Role
Structural Engineer/Designer
Services Provided
The scope of services includes the preparation of comprehensive structural calculations and structural drawings for the proposed structure. Structural calculations shall include complete loading analyses for wind, seismic, dead, and live loads in accordance with the applicable building codes and project site conditions. The work shall cover the structural analysis and design of all major structural components, including foundations, steel columns, steel beams, cold-formed steel (CFS) floor joists, CFS roof joists, and all necessary steel connections. These calculations will ensure that all structural members are adequately designed to safely resist gravity and lateral loads while maintaining a continuous and code-compliant load path throughout the structure.
Structural drawings shall include a Foundation Plan showing the layout and configuration of all foundation elements; Floor Framing Plans indicating the arrangement and sizing of steel beams and CFS floor joists; and a Roof Framing Plan illustrating the structural layout of CFS roof joists and supporting members. The drawings shall also include steel framing elevations organized per gridlines to clearly communicate member locations, sizes, and structural relationships. In addition, the drawing set will provide detailed structural sections, connection details, general structural notes, and specifications necessary for proper coordination, permitting, and construction implementation, ensuring that the design intent is clearly communicated for accurate field execution.