Shed and equipment pads are usually reinforced slabs over a compacted base, while workshops, garages, additions and ADUs need thicker slabs and engineered footings. Permitted work in California requires a CSLB-licensed contractor, and many San Diego sites need a soils report because of expansive clay, fill or slopes. Call 811 before digging.
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Sheds, workshops, detached garages, spa pads, equipment pads, room additions and accessory dwelling units (ADUs) all need a solid base. San Diego has seen a lot of ADU and addition work in recent years, and that work is usually permitted, inspected and engineered. A simple shed pad is a much smaller job, but it still depends on what the soil is doing underneath.
Common slab and foundation projects
- Pads for storage sheds, playhouses and garden studios
- Slabs for workshops, detached garages and carports
- Pads for spas, generators, HVAC and pool equipment
- Footings and slabs for room additions and ADUs
Small structures and pads
A shed or equipment pad is usually a reinforced slab over a compacted base, often with a thickened edge. Size it to the building plus a little extra, keep it level for the structure but draining at the edges, and confirm setbacks from property lines, easements, slopes and septic systems where they exist. Cities in San Diego County set their own size limits for when an accessory structure needs a permit, and HOAs often add rules, so check before you pour.
Workshops and garages
Slabs that hold vehicles or heavy equipment need more thickness and reinforcement than a shed pad, plus footings or thickened edges under the walls. If the space will be finished or air-conditioned, ask about a vapor retarder, insulation and where plumbing and electrical conduit should be placed before the pour.
Additions and ADUs
Foundations for living space must follow the California Building Code and Residential Code as adopted by your city. That usually means plans, a permit, inspections before concrete is placed, and on many sites a soils report. San Diego County's geology review notes that where high shrink-swell soils are present, structural standards in the building code apply through the permit process, and a geotechnical investigation is often required. Expansive clay, fill and slopes are common reasons an engineer specifies deeper footings, a post-tensioned slab or other measures.
Licensing
In California, the Contractors State License Board licenses concrete contractors (C-8) and general building contractors (B). Any job that needs a permit requires a licensed contractor, no matter the price, unless you are acting as an owner-builder under the rules your city explains. On an addition or ADU, the concrete crew often works under a general contractor who holds the permit, so be clear about who is responsible for what.
San Diego site factors
- Expansive clay: common on coastal mesas and in some foothill valleys. Soil prep and footing depth are design questions, not guesses.
- Hillside lots: slabs near slopes may need setbacks and engineered footings.
- Granite and rock: inland areas like Poway and Escondido can hit decomposed granite or solid rock during excavation, which changes equipment and cost.
- Seismic design: California's code includes seismic requirements that affect how slabs and walls connect.
- Utilities: California law requires calling 811 (DigAlert in Southern California) at least two working days before digging.
Questions to ask
- Does this project need a permit and a soils report, and who handles them?
- What thickness, reinforcement and base are included?
- Are inspections scheduled before the pour?
- What's your CSLB license number and classification?
Planning a building, ADU or addition? Request a slab or foundation contractor and include the structure's size and use. Our guide to hiring a concrete contractor in California covers licenses and contracts.
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Frequently asked questions
Do I need a permit for a shed slab in San Diego County?
It depends on the city and the size of the structure. Each city sets its own threshold for accessory buildings, and HOAs often have rules too. Check with your city's building department before pouring.
Does a concrete contractor need a license in California?
Yes, unless the whole job is under $1,000, needs no permit and uses no employees. The CSLB's C-8 classification covers concrete work, and general building contractors (B) also pour foundations.
Why does my ADU need a soils report?
Many San Diego lots have expansive clay, compacted or uncompacted fill, or slopes. A geotechnical report tells the engineer how to design footings and slab for that soil, and cities often require one for new living space.
Sources and further reading
- American Concrete Institute (ACI)
- Portland Cement Association (PCA)
- California Contractors State License Board: C-8 Concrete Contractor
- CSLB: License requirement for minor work increases to $1,000 (AB 2622)
- County of San Diego General Plan Update EIR: Geology and Soils (expansive soils)
- City of San Diego Development Services: Information Bulletin 165, Public Right-of-Way Permits
- City of San Diego Transportation Department: Sidewalk maintenance responsibility
- City of San Diego Stormwater
- California Department of Water Resources: Model Water Efficient Landscape Ordinance
- County of San Diego: Excavation Permit Brochure (DigAlert notice)
- DigAlert: Underground Service Alert of Southern California (811)