ADU Structural Engineering — Permit-Ready Drawings for Accessory Dwelling Units

Accessory Dwelling Units are one of the most active project types across California, Washington, and Texas right now. Whether you’re building a detached backyard cottage, a garage conversion, or an attached ADU above an existing structure, the structural engineering requirements are real — and getting them right the first time is what keeps your ADU project on schedule and on budget.

LPL Consultants delivers PE/SE-stamped ADU structural packages tailored to your state’s code requirements, your site conditions, and your building department’s submittal standards.

• Detached ADU (DADU): standalone structure in the backyard — new foundation, framing, lateral system
• Attached ADU: addition to the existing home — requires analysis of the existing structure and connection to new work
• Garage conversion ADU: existing garage converted to living space — often requires new roof framing, lateral reinforcement, and foundation evaluation
• Junior ADU (JADU): interior conversion within existing footprint — structural scope varies based on existing conditions
• Second-story ADU: ADU built above an existing garage or structure — requires full structural analysis of existing gravity and lateral system

• Foundation design: new slab, continuous footing, or connection to existing foundation
• Gravity framing: floor and roof framing layout, beam sizing, and connection details
• Lateral design: shear wall layout and holdown schedule for seismic (CA/WA) or wind (TX/FL)
• Existing structure evaluation (for attached, garage conversion, or second-story ADUs)
• Structural calculations for plan check
• Stamped drawings: PE/SE stamp for the project’s state
• Plan check response coordination

California ADU Structural Engineering

California’s ADU law has made it easier to build ADUs, but structural requirements remain fully enforced. Seismic design categories, CBC lateral requirements, and CalGreen provisions apply. We provide California-licensed PE/SE stamped ADU structural packages — fast turnaround, designed to pass plan check.

Washington ADU Structural Engineering

King, Pierce, and Snohomish counties have active ADU programs. Washington seismic demands apply even to small ADUs. We provide Washington-licensed PE stamped structural packages for Seattle-area DADUs and attached ADUs.

Texas ADU Structural Engineering

Texas municipalities are opening up to ADUs rapidly. Wind load design governs Texas ADU structures. We provide Texas-licensed PE stamped structural packages compliant with local city requirements.

Do I need a structural engineer for an ADU?

In most cases, yes. Any ADU that requires a building permit — which is virtually all ADUs except certain pre-approved standard plans — requires stamped structural drawings from a licensed engineer. Garage conversions and attached ADUs that modify the existing structure also require engineering review.

How long does ADU structural engineering take?

A straightforward detached ADU on a flat site typically takes 2–3 weeks from kickoff to permit-ready drawings. Attached ADUs, second-story ADUs, or projects on hillside sites take longer — typically 4–6 weeks. We provide a timeline at project kickoff based on your specific ADU type and site conditions.

Can LPL use pre-approved ADU standard plans?

Yes. Many California cities offer pre-approved ADU standard plans. We can review whether your project qualifies, adapt the standard plan to your specific site conditions if required, and provide supplemental engineering if your jurisdiction requires site-specific structural input even with a pre-approved plan.

ADU project ready for structural engineering? Let’s get your package on the schedule.