Building an ADU in Fullerton
Fullerton is known for its historic neighborhoods, tree-lined streets, and homes close to the university and downtown. If you own a home here, an ADU can be a practical way to house family, earn rental income, or add flexible space without leaving the neighborhood you love. Lamarc Prime Builders designs and builds detached ADUs, attached additions, and garage conversions for Fullerton homeowners. We plan around the city’s rules on exterior materials, roof slope, parking, and water and sewer capacity, and we manage your project from the first design sketch through final inspection.
ADU Services Available in Fullerton, CA
We help Fullerton homeowners plan and build ADUs that balance comfort, usability, and code compliance. From layout decisions to permitting details and construction execution, our team manages each phase so your project stays clear and moving forward.
✅ Detached & Attached ADUs
✅ Garage Conversion ADUs
✅ Junior ADUs (JADUs)
✅ ADU Planning & Design Coordination
✅ Permits, Plan Submittals & City Revisions
✅ Construction, Inspections & Final Completion
Want a realistic path forward? Begin with a free site evaluation and we’ll outline the next steps for your property.
ADU Rules in Fullerton
ADUs allowed per lot
1 ADU + 1 JADU; up to 2 detached ADUs on R-1 and R-2 lots of 1+ acre
Max detached ADU size
Up to 1,200 sq ft
Max attached ADU size
850 sq ft (studio or 1 bedroom); 1,000 sq ft (2+ bedrooms)
Max JADU size
Up to 500 sq ft
Max height (detached)
16 ft (18 ft near major transit) + up to 2 ft for roof pitch
Two-story ADU
Attached ADUs up to 25 ft or your zone's limit, max two stories
Setbacks
4 ft side, street-side, and rear
Space between buildings
We confirm for your lot
Parking
1 space (none for a studio); none near transit, for conversions, or in historic districts
Owner occupancy
Not required for an ADU; JADU requires the owner to live on site
Short-term rental (Airbnb)
31-day minimum; no Airbnb
Impact fees
None under 750 sq ft; larger ADUs pay proportionally
Pre-approved plans
30-day review for a pre-approved or identical previously approved detached plan
Permit review
Ministerial review under city code; no hearing
Approval timeline
60 days (30 days with a pre-approved plan)
Local insight
Fullerton gives a faster 30-day decision for detached ADUs that use a pre-approved or previously approved identical plan. ADUs on California Register historic properties must also meet the city's historic standards.
How ADU Permitting Works in Fullerton
Fullerton reviews ADUs ministerially, with no public hearing and no discretionary design review. A detached ADU that uses a plan the city has pre-approved, or a plan identical to one it approved within the current code cycle, gets a faster decision. Everything else goes through standard review with custom plans. If you’re replacing a detached garage, the demolition permit is reviewed and issued with the ADU application, and the city checks water and sewer service at your address, so we look at that early.
Property feasibility review
Review zoning, lot conditions, access, utilities, and applicable ADU requirements.
ADU design and preparation
Prepare the site plan, architectural drawings, engineering, and required supporting documents.
City plan review and approvals
Submit the application, coordinate with city departments, and respond to plan-check corrections.
Permit issuance and construction
After approval and permit issuance, proceed with construction and required inspections.
FAQs About ADUs in Fullerton
Can my Fullerton ADU get the faster 30-day review?
Possibly. The shortcut applies to a detached ADU that uses a pre-approved plan, or a plan identical to one the city already approved within the current building code cycle. We can tell you whether that is available for your project.
Can I use custom ADU plans instead of pre-approved plans in Fullerton?
Yes. Custom plans go through standard ministerial review. A custom design lets us fit the ADU to your lot and match your main home’s exterior materials, colors, windows, doors, and roof slope.
What documents are required to submit an ADU permit application in Fullerton?
You submit the city’s ADU application with a complete plan set and pay an application fee plus plan check, inspection, and permit fees. If you’re replacing a detached garage, the demolition permit is reviewed with the ADU. The city also checks that water and sewer service is adequate at your address. We prepare the package.
Can I convert an existing garage into an ADU in Fullerton?
Yes. No parking is required for an ADU inside your main home or an accessory structure, and if you’re replacing a detached garage, the demolition permit is issued with the ADU application. We check the structure and your lot before drawing plans.
How can Lamarc Prime Builders help with ADU design, permitting, and construction in Fullerton?
We handle the whole project in one place. We start with a feasibility review of your lot, prepare the design, drawings, and engineering, submit to the City of Fullerton and respond to plan-check corrections, and then build your ADU through final inspections.
