New Two-Story Accessory Dwelling Unit

Project Details

This project involves the structural design and engineering of a new two-story accessory dwelling unit (ADU). The comprehensive scope required modern engineering solutions for the entire structural assembly, including cold-formed steel (CFS) framing, floor trusses, and roof trusses, all supported by a specifically designed foundation system. The primary structure utilizes high-strength G60 galvanized steel meeting ASTM A 1003 Grade ST50H with a minimum yield strength of 50 KSI, integrated with specialized connectors and clips to ensure a durable and lightweight assembly. The design process included a rigorous structural analysis to ensure the dwelling could safely withstand specified environmental loads, including a roof live load of 20 psf and a floor live load of 40 psf. The structural elements were engineered in accordance with the 2021 International Building Code (IBC), the 2025 California Building Code (CBC), and ASCE 7-16 provisions. Special attention was given to lateral load resistance through the implementation of engineered shear walls utilizing 15/32″ Structural-1 sheathing with precision screw patterns, providing stability against wind speeds of 95 MPH (Exposure C) and meeting requirements for Seismic Design Category D. The foundation system features a sophisticated combination of reinforced concrete grade beams and pedestals integrated with helical screw piles, designed to perform reliably under an allowable soil bearing pressure of 4,000 psf.

Role

Structural Engineer/Designer

Services Provided

The scope of services included the preparation of structural analysis and design calculations for the proposed two-storey detached ADU. The work involved determining wind, seismic, dead, and live loads in accordance with the governing building code and performing a complete structural analysis and design of all structural components, including foundations, slab-on-grade or crawlspace systems, load-bearing walls, shear walls, columns, beams, built-up beams, floor framing, roof framing, diaphragms, holdowns, and connectors. Independent verification of all gravity and lateral force-resisting elements was conducted to confirm structural adequacy and a continuous load path throughout the structure. The services also included reviewing and addressing all notes identified on the Framecad reference layouts and coordinating the structural design with the IFC model to facilitate three-dimensional understanding and load path verification. Structural drawings were prepared to illustrate the foundation system, floor and roof framing, shear wall layouts, structural building sections, and all typical structural details, notes, and specifications required to clearly communicate the design intent and support permit review and construction.