Accessory Dwelling Units (ADUs) have exploded in popularity across Southern California. Lower costs, rental income potential, and relaxed state regulations have made them one of the most common residential construction projects in the region. But before you pour a single footing, most local building departments require a geotechnical investigation — commonly called a soil report — to confirm that subsurface conditions can safely support your new structure.
If you're planning an ADU in Ventura County, Santa Clarita, Glendale, or Burbank, here's what you need to know about soil report requirements, what the investigation involves, and how to keep your project on schedule.
A geotechnical soil report — also called a soils investigation or geotechnical report — is a document prepared by a licensed geotechnical engineer or engineering geologist that describes the subsurface conditions at your property and provides recommendations for foundation design.
For an ADU, a typical geotechnical investigation includes:
The final report is stamped by a licensed professional and submitted to the building department as part of your permit application.
Ventura County encompasses a wide range of geologic conditions — from the alluvial valleys near Oxnard and Camarillo to the hillside terrain of Thousand Oaks, Moorpark, and Simi Valley. The Ventura County Building and Safety Division routinely requires geotechnical reports for ADUs on hillside lots, properties with expansive soils, or sites near active fault zones.
Key considerations for Ventura County ADU projects include proximity to the San Andreas, Simi, and Santa Rosa fault systems, expansive clay soils common in the inland valleys, and slope stability on hillside and canyon lots. Even on flatter parcels, expansive soils can cause significant foundation movement if not properly addressed in the design. GeoTed serves Thousand Oaks, Simi Valley, Camarillo, Oxnard, Ventura, and surrounding unincorporated areas.
Santa Clarita sits at the northern edge of Los Angeles County in a geologically active corridor. The area is underlain by sedimentary formations that can include compressible soils, expansive clays, and fill from prior grading. The Santa Clarita Valley is also adjacent to several active fault zones including the San Andreas fault system.
The City of Santa Clarita building department typically requires a geotechnical report for ADUs on lots with slopes, fill soils, or expansive soil conditions. For detached ADUs with new foundations, a soils report is commonly required regardless of slope. GeoTed regularly performs ADU soil investigations in Valencia, Newhall, Stevenson Ranch, Saugus, and Canyon Country.
Glendale presents some of the most complex geologic conditions for ADU construction in the San Gabriel Valley. Much of Glendale is underlain by the Verdugo Mountains to the north and transitional soils toward the LA basin to the south. The City of Glendale Building and Safety Department requires geotechnical reports for most ADU applications, particularly on hillside lots, steep terrain, and properties near landslide areas.
Glendale-specific concerns include landslide and debris flow hazard zones in hillside neighborhoods, proximity to the Verdugo fault, and liquefiable soils in lower-lying areas near the Los Angeles River. GeoTed provides geotechnical evaluations for ADU projects throughout Glendale including the Montecito Park, Chevy Chase Canyon, and La Crescenta-Montrose areas.
Burbank sits in the eastern San Fernando Valley at the foot of the Verdugo Hills. The area is underlain by alluvial fan deposits from the Verdugo Mountains, with variable soil conditions including loose sands, silts, and clay layers depending on location. The Burbank Building Division requires geotechnical reports for ADUs where soil conditions, slope, or existing fill may affect foundation performance.
Common issues for Burbank ADU projects include settlement-prone alluvial soils, variable fill from older grading, and potential liquefaction in certain zones. GeoTed serves ADU projects across Burbank including residential neighborhoods in the foothills and flatlands near Magnolia Park and downtown Burbank.
While requirements vary by jurisdiction, a geotechnical soil report is typically required for an ADU when:
Even when not strictly required, a geotechnical evaluation is strongly recommended for any ADU on a hillside lot, a site with drainage problems, or a property with a history of foundation movement or cracking.
A typical ADU geotechnical investigation in Southern California takes 1–2 weeks from initial site visit to final stamped report delivery. GeoTed offers fast-turnaround investigations designed to keep your project on schedule, with site visits typically available within a few days of engagement.
The process generally follows this timeline:
The cost of a geotechnical soil report for an ADU in Southern California typically ranges from $1,500 to $4,500 depending on the scope of investigation, site access, and local requirements. GeoTed provides competitive fixed-fee proposals for standard ADU investigations with no surprise charges.
A soil report is one of the smallest line items in an ADU project budget — and one of the most important. Skipping or delaying the geotechnical work is one of the most common causes of plan check rejections and construction delays on ADU projects.
GeoTed specializes in geotechnical and geological evaluations for residential and small-site projects across Southern California. Unlike large corporate firms focused on commercial and infrastructure work, we focus exclusively on the scale of projects where subsurface conditions directly affect homeowners — ADUs, additions, pools, retaining walls, and property transactions.
Our licensed engineers and geologists are familiar with local building department requirements in Ventura County, Santa Clarita, Glendale, Burbank, and across greater Los Angeles. We provide clear, practical reports that satisfy plan check requirements and give your design team the information they need to build confidently.
Contact GeoTed today to discuss your ADU project and get a fast, fixed-fee proposal for your soil investigation.
