Do You Need a Building Permit in California? ADUs, Solar, and Exemptions

In California, you need a building permit for almost any project that changes a structure or its plumbing, electrical, or mechanical systems, including additions, remodels, decks, pools, retaining walls, water heater swaps, new circuits, and furnace installations. The 2025 California Building Standards Code sets the statewide baseline, but your city or county building department is the office that reviews plans and issues the permit.¹ A short list of small projects is exempt, and skipping a required permit is far more expensive than pulling one.

What Triggers the Permit Requirement

The California Building Code says anyone who intends to build, enlarge, alter, repair, move, or demolish a structure must apply for and receive a permit before any work begins.² The same rule covers installing or replacing electrical, gas, mechanical, or plumbing systems.

The trigger is low. Moving a load-bearing wall requires a permit. So does rerouting a water line, adding an electrical circuit, replacing a water heater, or installing a furnace. Exterior projects get the same scrutiny as new buildings: decks, swimming pools, retaining walls, and room additions. Large-scale renovations that change a home’s layout or structural skeleton also fall under the rule. The point of the permit is to let an inspector verify that your work meets current seismic, fire-safety, and energy standards before it gets buried behind drywall.

Projects That Don’t Need a Permit

The California Building Code carves out specific exemptions for small, low-risk projects:³

One-story detached tool sheds, playhouses, and similar accessory buildings with a floor area of 120 square feet or less.
Fences seven feet tall or shorter, excluding swimming pool barriers, which have separate safety requirements.
Prefabricated above-ground pools less than 24 inches deep and under 5,000 gallons.
Window awnings on residential buildings, supported by the exterior wall and projecting no more than 54 inches, with no additional support needed.
Interior painting, wallpapering, tiling, carpeting, and similar cosmetic finishes that don’t alter the structure.
Cabinet and countertop replacement, provided you aren’t moving plumbing lines or electrical outlets in the process.

Being exempt from a permit is not the same as being exempt from all rules. Your project still has to comply with local zoning ordinances covering setbacks, height limits, and property-line clearances. Local jurisdictions can also impose stricter thresholds than the state code, so confirm with your building department before assuming an exemption applies to your project.

Accessory Dwelling Units

ADUs are one of the most common permit applications in California, and state law tilts the process toward approval. Local agencies must process an ADU application on a ministerial basis, applying objective published standards rather than discretionary judgment. Your building department has 15 business days to tell you whether your application is complete, then 60 days from the date of a complete application to approve or deny it.⁴

Size limits depend on whether your city or county has adopted its own ADU ordinance. A local ordinance must allow at least 850 square feet for a studio or one-bedroom and at least 1,000 square feet for two or more bedrooms. Where no compliant local ordinance exists, the state defaults apply: up to 1,200 square feet for a detached ADU, or up to 50 percent of the existing home’s floor area for an attached unit, with a minimum of 800 square feet.⁴

Setbacks for a new detached or attached ADU cannot exceed four feet from side and rear lot lines. Converting existing living space or an existing accessory structure requires no setback at all. Height limits are generally 16 feet for a detached ADU, rising to 18 feet on lots near a major transit stop or on lots with a multistory building. Local agencies cannot use lot coverage, floor-area-ratio, or open-space rules to block an ADU of at least 800 square feet that meets those four-foot setbacks.⁴ If your application is denied, the permitting agency must provide a written appeal process and has 60 business days after receiving your appeal to issue a final determination.

Rooftop Solar

Residential rooftop solar needs both a building permit and an electrical permit, but California law requires every city and county to offer an expedited, streamlined process for systems that qualify. Under AB 2188, a residential solar energy system of 10 kilowatts or less on a single-family or duplex home that does not exceed the building’s maximum legal height is eligible for fast-track approval.⁵

Once the building department confirms your application is complete and meets the checklist, the permit should be issued. Best-practice guidance calls for that review to happen within one business day and no longer than three. Only one inspection is required for eligible installations, and if multiple agencies need to inspect, they must do so at the same time. Cities cannot condition solar permit approval on homeowners’ association approval, and they must accept electronic applications and electronic signatures.⁵

What Happens If You Skip the Permit

The financial risk of working without a required permit is much larger than the permit fee itself. California jurisdictions commonly charge double or triple the normal fee when you apply retroactively, on top of fines that can start at several hundred dollars and escalate. A stop-work order halts all activity on the site until the situation is resolved, which can wreck project timelines and contractor schedules.

The bigger problem shows up at sale. California requires sellers of single-family homes to disclose room additions, structural changes, and other alterations made since purchase, along with any permits obtained for that work. A seller who willfully or negligently fails to make those disclosures can be sued by the buyer for actual damages.⁶ Even without a lawsuit, an appraiser or buyer’s inspector who spots unpermitted work will flag it, and that can kill a deal or force a price reduction.

Getting a retroactive permit is possible but rarely pleasant. You’ll need to submit as-built plans showing work that’s already done, pay the penalty-adjusted fees, and open up walls or ceilings so an inspector can verify hidden systems. If anything doesn’t meet code, you’re responsible for bringing it up to current standards, which can cost significantly more than doing it right the first time.

How a Permit Affects Your Property Taxes

Filing a permit creates a public record, and county assessors use those records to identify properties that may have increased in value. Under California’s Revenue and Taxation Code, “new construction” includes any addition to real property and any alteration that qualifies as a major rehabilitation or converts the property to a different use.⁷ A major rehabilitation means work that turns an improvement into the substantial equivalent of a new one.

When the assessor determines that new construction has occurred, a new base-year value is established for the improvement. The reassessment applies only to the added value of the new work; the existing property’s assessed value stays protected under Proposition 13.⁸ Add a $150,000 room addition to a home assessed at $400,000, and the assessor adds the market value of the new construction to the existing base; the original home is not reassessed at current market rates.

Cosmetic updates like repainting, replacing carpet, or swapping out fixtures generally don’t qualify as new construction and shouldn’t change your tax bill. Work done solely to repair disaster damage also gets protection: timely reconstruction to a substantially equivalent condition is not treated as new construction.⁷

Contractor vs. Owner-Builder

California law requires a contractor’s license for any project that needs a building permit or where the total cost of labor and materials reaches $500 or more.⁹ An unlicensed contractor cannot file a lawsuit to collect payment for work performed, and the homeowner who hired them can sue to recover every dollar already paid.¹⁰

You can also pull the permit as an owner-builder and act as your own general contractor. Under Health and Safety Code Section 19825, every jurisdiction that issues building permits must collect a signed Owner-Builder Declaration and verify the property owner’s identity before issuing the permit.¹¹

Signing that form carries real consequences. As an owner-builder, you take personal responsibility for code compliance, scheduling all required inspections, and supervising every subcontractor on the job. If you hire workers who aren’t licensed contractors, you may be treated as their employer under state and federal law, which means withholding taxes, paying into Social Security, and carrying workers’ compensation insurance. Your homeowner’s insurance likely won’t cover injuries to unlicensed workers on a construction site, so an on-site accident could land squarely on you financially. A mechanic’s lien from an unpaid subcontractor can also cloud your title and make it impossible to refinance or sell until the lien is resolved. For small projects you’re confident handling, owner-building is a reasonable path. For anything structurally complex, the cost of a licensed contractor is cheap insurance.

Once You Have the Permit

A California building permit remains valid as long as work begins within 12 months of issuance.¹² Pull a permit and let it sit untouched for more than a year and it expires; you’ll need to reapply, repay fees, and possibly update your plans to reflect code changes that took effect in the meantime. Extensions are available in many jurisdictions, but if the building department determines the permitted work has been abandoned, an extension will be denied. Don’t pull a permit until you’re genuinely ready to start.

Once construction begins, your inspection card must be posted visibly at the job site, and each stage of work (foundation, framing, rough-in plumbing and electrical, insulation, and final) must be signed off before the next one begins. Scheduling those inspections is your responsibility. If an inspector arrives and the relevant work is already hidden behind drywall or concrete, you’ll be asked to open it back up at your own expense.

One protection worth knowing: if you complete permitted work and notify your local building department, but the department fails to conduct an inspection within 60 days of receiving that notice, you’re entitled to a refund of your permit fees.¹³ The department is required to disclose this right on the permit itself or on an accompanying document.

1
California Department of General Services. Building Standards Commission – Codes
2
ICC Digital Codes. 2022 California Building Code Title 24 Part 2 – Section 105.1
3
El Dorado County. Exemption from Permit – 2025 CBC Title 24 Vol 1 Section 105-105.2.3
4
California Department of Housing and Community Development. Accessory Dwelling Unit Handbook March 2026
5
California Department of Housing and Community Development. AB 2188 Streamlined Residential Rooftop Solar Permitting
6
California Senate Judiciary Committee. AB 968 (Grayson) Analysis
7
California Legislative Information. California Code Revenue and Taxation Code RTC 70
8
California State Board of Equalization. New Construction – Property Taxes
9
Contractors State License Board. Building Official Information Guide
10
California Legislative Information. California Code Business and Professions Code BPC 7031
11
California Legislative Information. California Health and Safety Code HSC 19825
12
California Department of General Services. Part 2 Chapter 1 Scope and Administration
13
California Legislative Information. California Health and Safety Code HSC 17951