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Building an ADU?

Building an ADU? Here's every engineering deliverable your project is likely to need.

ADU Permitting Is Easier — ADU Engineering Isn't Optional

California's ADU legislation has streamlined the permitting process, but it hasn't changed the engineering requirements. You still need a foundation that works for your soil. You still need drainage that doesn't flood your neighbor. And the building department still requires the reports and plans that prove it.

Most ADUs require a soils report and a grading plan. Some need stormwater compliance documentation (LID or WQMP). A few trigger street improvement requirements. The exact list depends on your jurisdiction, your lot conditions, and your project scope.

We scope every ADU individually, research the jurisdiction-specific requirements, and send one proposal that covers everything — geotech and civil engineering under one scope, one fee, one contact.

What You'll Need

Engineering deliverables for adu projects:

Usually Required

🔩

Soils Report

Required for most detached ADUs with new foundations. Determines bearing capacity, foundation type, seismic parameters, and earthwork specifications. Some jurisdictions waive for attached ADUs on flat lots with an existing report on file.

Usually Required

📐

Grading Plan

Required when the ADU involves any site grading — new pad, drainage modifications, retaining walls. Shows cut/fill, finished grades, drainage flow, and setbacks. Even flat-lot ADUs often need a basic grading plan for drainage.

If Grading

🏗

Compaction Testing

Required during construction if the soils report specifies engineered fill or a prepared building pad. Our technicians verify earthwork meets compaction specifications before the foundation goes in.

Varies

💧

LID / WQMP

Triggered in some jurisdictions when the ADU adds significant impervious area. San Diego uses LID; Orange County and LA use WQMP. Threshold varies by jurisdiction.

Varies

🛣

Street Improvements

Some cities require frontage improvements as a condition of the ADU permit — sidewalk, curb, ADA ramp. Others exempt ADUs. We research your jurisdiction's specific requirements during scoping.

Rare

🌧

Hydrology Report

Typically not required for a single ADU on a flat lot. But if the project significantly changes drainage patterns or the lot is on a slope, a hydrology study may be required.

Jurisdiction Matters More Than You Think

ADU requirements vary significantly between cities and counties. What's waived in one jurisdiction is mandatory in the next. San Diego County may exempt your ADU from stormwater requirements while the City of San Diego requires a full LID report. LADBS has specific hillside ADU requirements that don't exist in Orange County.

This is why we research your specific jurisdiction's requirements before sending a proposal. We've worked across San Diego, Orange County, and Los Angeles — we know which agencies require what, and we scope accordingly.

Counties — San Diego, Orange, Los Angeles — each with different ADU requirements

50+

Jurisdictions with unique permitting standards that affect your ADU scope

Proposal covers everything — geotech and civil under one scope, one contact

What to Expect

Proposal & Scoping

We review your plans and site conditions, research jurisdiction-specific requirements, and send a fixed-fee proposal with every deliverable your ADU needs.

Field Work

If a soils report is required, we drill borings and collect samples. Most ADU sites are a single-day mobilization. Sloped sites may need additional investigation.

Engineering & Plans

We prepare your soils report, grading plan, and any additional deliverables. Everything is coordinated — the grading plan references the soils report recommendations, ready for simultaneous submittal.

Plan Check & Construction

We support your submittal through plan check. Corrections on our original scope included. During construction, we provide compaction testing and field inspections as needed.

Building Something Else?

Hillside Development Guide

Slope stability, specialized foundations, and hillside engineering requirements.

Read Guide →

Retaining Wall Engineering

When you need geotech for walls, and what's involved.

Read Guide →

Pool Engineering Guide

Pool soils reports and foundation engineering.

Read Guide →

Common Questions

In most jurisdictions, yes — especially for detached ADUs with new foundations. Some cities waive the requirement for attached ADUs or ADUs on flat lots where an existing report covers the site. We check the specific requirements for your project during scoping.

It depends on the report's scope and age. If the existing report covers the ADU location and the recommendations are compatible with the proposed foundation type, some jurisdictions will accept it — possibly with an update letter. We review the existing report and advise.

Usually, yes. Even on flat lots, the building department typically requires a plan showing finished grades and drainage around the new structure. On sloped lots, a full grading plan with cut/fill quantities and retaining wall design is almost always required.

It varies significantly by jurisdiction. Some cities exempt ADUs from LID/WQMP requirements. Others trigger stormwater compliance when you exceed a certain impervious area threshold. We research your specific jurisdiction's requirements before scoping.

From field work to report delivery, typically a few weeks for the geotechnical report and a similar timeframe for the grading plan. We can often coordinate so everything is ready for submittal at the same time.

Ready to Get Your ADU Started?

Tell us about your adu project and we'll send a proposal with every deliverable you need — scope, fee, and timeline.

Request a Proposal Talk to an Engineer