
California structural & civil engineers specializing in basement ADUs, delivering code-compliant structural and civil engineering plans for below-grade ADU conversions throughout California. Typical turnaround for structural & civil plan sets is 2-3 weeks. Unlimited plan-check revisions within our engineering scope(1) at no extra cost.
Build your basement ADU with confidence. We engineer below-grade ADU conversions—assessing existing foundations and framing, designing structural modifications for habitable use, and addressing seismic loads, soil interaction, and below-grade code requirements—delivering permit-ready PE-stamped plans for your property.
Serving all 58 California counties with expert Basement ADU structural engineering.
Share a few project details and our engineering team will review your scope and guide you through permitting and design next steps.
After reviewing your project details, we'll provide a transparent quote the same day--typically within a few hours. Pricing varies based on project scope, complexity, and requirements.
We deliver complete structural permit sets. *If building departments have comments related to our scope, we handle all revisions--no extra fees, no limits.
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A basement ADU is an accessory dwelling unit created by converting below-grade space within the primary residence into a separate dwelling unit. Basement ADUs utilize existing below-grade space, requiring structural assessment of existing foundations and framing to ensure they meet code requirements for habitable space. California building codes require PE-stamped structural plans for all basement ADU projects to verify structural capacity and compliance.
Basement ADU structural & civil engineering costs in California vary based on project size, complexity, existing structure condition, and the extent of structural modifications required. Our pricing includes structural assessment of existing foundations and framing, structural calculations, foundation capacity analysis, structural modification design, framing plans, lateral system design, civil engineering coordination, and PE-stamped permit-ready structural & civil engineering plans. We provide same-day quotes with transparent, fixed pricing--no hidden fees or surprises. Contact us for a free quote specific to your basement ADU project.
Yes, California requires PE-stamped structural plans for all basement ADU projects. Structural engineering is mandatory for structural assessment of existing foundations and framing, foundation capacity analysis, structural modifications, load path design, lateral force-resisting systems, and seismic safety compliance with California building codes. Basement ADUs require structural evaluation of the existing structure to ensure it can accommodate the new use.
Typical turnaround for structural & civil plan sets for basement ADU projects in California is 2-3 weeks. This includes site evaluation, structural assessment of existing foundations and framing, structural calculations, foundation capacity analysis, structural modification design, framing plans, lateral system design, civil engineering coordination, and complete plan sets. Rush services available for urgent projects.
Basement ADU conversions require structural assessment of existing foundations and framing to ensure they can accommodate the new use. Key considerations include foundation structural capacity under new loads, existing framing system evaluation, load path analysis from primary residence through to foundation, soil interaction and lateral earth pressure, and structural modifications needed for below-grade habitable space. We provide structural engineering services including foundation capacity analysis, existing framing assessment, structural modification design, load path design, and lateral force-resisting system design specific to below-grade conversions.
Under California ADU law, basement ADUs can be up to 850 square feet for attached ADUs, or up to 1,200 square feet if the basement ADU qualifies as a detached ADU (though basement ADUs are typically attached). Specific limits may vary by local jurisdiction. Our structural engineering services accommodate basement ADUs within these size parameters, providing complete structural analysis and design that accounts for existing structure capacity and below-grade conditions.
Basement ADUs typically utilize existing foundations, but require structural assessment to verify foundation capacity under new loads. We provide structural analysis and foundation capacity evaluation for basement ADUs, including load-bearing capacity calculations, foundation structural assessment, and verification that existing foundations can accommodate the new use in compliance with California building codes. Foundation capacity must account for existing loads, new ADU loads, seismic loads, and soil characteristics specific to the project site.
Basement ADU projects may require civil engineering services including site coordination, grading design, and drainage design, particularly for below-grade conditions. We provide high-level civil engineering coordination for basement ADU projects, ensuring proper site layout, drainage considerations for below-grade spaces, and grading requirements are addressed in coordination with structural design. Civil engineering services are provided at a high level and coordinated with structural plans.
California cities and counties use various permitting systems--some online, some in-person. We provide complete PE-stamped structural & civil engineering plan sets in PDF format ready for submission. Our plans include all required structural and civil engineering sheets, calculations, existing structure assessment, and documentation needed for plan check. We also respond to all building department comments throughout the review process.
Yes, we offer construction administration services for basement ADU projects including: responding to contractor RFIs, reviewing shop drawings and submittals, site visits for structural observations, and certification letters. This ensures your basement ADU is built according to structural plans and code requirements.

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