California's ADU permitting landscape changed significantly in 2020 and has continued to improve since. What used to take 18+ months and significant legal effort can now, in many jurisdictions, be handled in under 60 days.

This guide covers the current state of the process — what you actually need, what common hurdles look like, and how to move through it without losing momentum.

What Changed in California After 2020

A series of state bills — most significantly AB 68, AB 881, and SB 13 — overhauled California's ADU rules. Here's what actually shifted for homeowners:

Owner-occupancy requirements removed. You no longer need to live on the property to build or rent an ADU.

Setback rules relaxed. Most ADUs can now be built within 4 feet of rear and side property lines, opening up lots that were previously ineligible.

Fees reduced. Cities can no longer charge impact fees on ADUs under 750 sqft.

Permit timelines mandated. Local agencies must act on ADU applications within 60 days — and in practice, many process faster.

Pre-approved plans. Many California cities now offer pre-approved ADU plans that skip the design review phase entirely, reducing timelines to 21–30 days.

What You'll Need to Submit

Requirements vary by city and county, but a standard ADU permit application typically includes:

Site plan — showing the location of the proposed unit on the lot, property lines, setbacks, and existing structures.

Floor plan and elevations — showing the unit layout, dimensions, door/window placement, and height. If you're using a prefab unit like a Kasita, the manufacturer provides these documents.

Utility plan — showing how the ADU will connect to water, sewer, and electrical. This is often the most complex part of the application for lots with older infrastructure.

Title 24 energy compliance — California requires energy compliance documentation for any new dwelling unit. Factory-built units from certified manufacturers typically come with this documentation pre-completed.

Structural calculations — required for any unit over 500 sqft or any unit on a foundation.

Zoning: Does Your Lot Qualify?

Under current California law, ADUs are permitted by right on any lot that contains a single-family residence or multi-family building, with limited exceptions. The key factors that determine what you can build are:

Lot size — minimum lot size requirements have been largely eliminated at the state level, though local rules can vary.

Setbacks — your ADU must maintain 4-foot rear and side setbacks in most cases. Front setbacks are stricter (typically matching your primary residence setback).

Height limits — detached ADUs are generally limited to 16 feet. Some jurisdictions allow taller units if the ADU is within a half-mile of public transit.

Parking — California ADUs do not require additional parking if the unit is within a half-mile of public transit or within one block of a car-share vehicle.

Realistic Timelines by Path

These are permit timelines only. Site prep, delivery, and installation add additional time — typically 2–6 weeks for a prefab unit.

Common Stumbling Blocks

Utility connection issues. Older lots sometimes have undersized water meters or sewer lines that need upgrading. This is the single most common source of delays and unexpected costs. We check for this during your property evaluation.

HOA restrictions. HOA-governed communities can restrict ADUs even under state law. Review your CC&Rs before applying.

Historic districts. Properties in designated historic districts may face additional design review requirements.

Fire sprinklers. Some jurisdictions require sprinklers in new ADUs. Requirements vary — check with your local building department.

How Kasita Makes This Easier

When you build with Kasita, we handle the permit documentation package for you. Our factory-built units come with:

• Pre-drawn floor plans and elevations

• Title 24 energy compliance documentation

• Structural engineering sign-offs

• HCD certification (California Department of Housing & Community Development)

You provide the site plan and utility information. We handle the rest.

Book a free property evaluation to find out exactly what your lot needs and what timeline to expect — before you spend anything.