A free site visit, a check of what your lot allows and a written, line-item price.
Get your free estimateADU Company in Fullerton, CA
An ADU in Fullerton lets you add a second home to a lot you already own, and the city’s older housing stock makes that decision more practical here than in most of Orange County. Fullerton homes tend to sit on lots that are wide enough for a detached unit but mature enough that the soil and utility runs need a close look before we ever draft a price. Call (472) 248-8213 and we’ll walk you through what your specific lot will actually support.
Why Fullerton Homes Are Different
Fullerton was built out in clear phases, and each one changes how an ADU job goes together. The neighborhoods north of Chapman Avenue, around Raymond Hills and the area east of Harbor Boulevard, include a large share of homes from the 1950s and 1960s. Those lots usually offer the easiest path to a detached ADU because the backyards are genuinely deep. The tradeoff is that the original electrical panels are often 100-amp, which means your project may include a service upgrade before the new unit ever gets wired in.
South Fullerton, including the neighborhoods near Sunny Hills and the area around Bastanchury Road, leans toward larger parcels with steeper grades in places. A modest slope can actually help with drainage on a slab foundation, but it adds to grading and retaining costs when the grade runs the wrong direction. We always walk the lot before we quote, because two Fullerton homes a block apart can have very different site costs.
Permitting goes through the City of Fullerton’s building division, which reviews ADU plans for compliance with state law and local setback rules. A setback is the required gap between your new structure and the property line. Fullerton follows California’s ADU mandate, so a detached unit under 1,200 square feet is generally allowed on any single-family lot, but there are still site-specific conditions like easements and heritage tree rules that need checking.
Our Main Fullerton Services
The two types of work Fullerton homeowners call us about most are adding a new detached ADU and pulling more square footage out of the home they already have. Each one has its own Fullerton page with pricing and process details.
Home Addition Contractor in Fullerton
A home addition in Fullerton means attaching new square footage to the existing structure, which brings every trade into the same footprint: framing, electrical, plumbing, and the roofline tie-in. On older Fullerton homes the existing foundation is usually sound but not always level, and that’s the part of the estimate we spend the most time on. Where the addition goes matters too: a rear addition off the kitchen in a Raymond Hills rancher usually moves faster than a second-story addition on a sloped Sunny Hills lot. Home Addition Contractor in Fullerton has the full breakdown, including how we price the foundation work that most quotes leave loose.
ADU Builders in Fullerton
A detached ADU in Fullerton is its own small house, with its own foundation, its own power, and its own address on your land. The lots here handle a 600 to 1,000 square foot unit well in most cases, and because Fullerton enforces the state ADU rules rather than layering on its own restrictions, the permitting path tends to be more predictable than in surrounding cities. Prefab options change the timeline and the disruption level on site. ADU Builders in Fullerton covers the difference between panelized, modular, and traditional construction, plus real price ranges for each.
Room Addition Contractor in Fullerton
A room addition is the smallest scope that still touches foundation, framing, and roofing, and in Fullerton it usually means one of two things: expanding a primary bedroom, or adding a family room off the back of the house. Because these projects live inside the existing structure’s envelope, the condition of your current roofline and shear wall becomes our problem to solve. Most Fullerton room additions take four to eight weeks once permits are issued, depending on whether we’re tying into the kitchen or the exterior wall. Room Addition Contractor in Fullerton explains what we inspect before quoting and how we handle the permit set.
What happens when you call
- 1
A real person answersNo phone trees - you reach a local pro.
- 2
You get an upfront price rangeHonest numbers before anyone is dispatched.
- 3
A background-checked tech heads outLicensed & insured, dispatched right away.
- 4
You approve before work beginsNothing starts until you say go.
Brands We Service in Fullerton
We work directly with Abodu, Cover, and Mighty Buildings on Fullerton ADU projects, and our team knows which model lines each brand offers that fit a typical Orange County lot. Parts lead times vary by brand; we review current order windows when we quote. See our brands for the full list.
Pricing for ADU Company in Fullerton, CA
| Service | Typical range in Fullerton |
|---|---|
| Detached ADU, 400 – 600 sq ft | $180,000 – $260,000 |
| Detached ADU, 600 – 800 sq ft | $240,000 – $320,000 |
| Detached ADU, 800 – 1,200 sq ft | $320,000 – $420,000 |
| Garage conversion to ADU (400 – 600 sq ft) | $120,000 – $190,000 |
| Home addition, ground level (300 – 500 sq ft) | $150,000 – $240,000 |
| Home addition, ground level (500 – 800 sq ft) | $220,000 – $340,000 |
| Second-story addition (500 – 800 sq ft) | $280,000 – $400,000 |
| Room addition, single room (150 – 300 sq ft) | $90,000 – $160,000 |
| Electrical service upgrade (100-amp to 200-amp) | $4,000 – $8,000 |
| Site grading and drainage correction | $6,000 – $18,000 |
What pushes a number up in Fullerton is usually the age of the existing home: older panels, cast-iron waste lines, and slab foundations that have shifted over sixty-plus years all add scope. What doesn’t change is how we quote it: you get a written price before any work starts, and that price is what you pay.
Neighborhoods We Serve in Fullerton
We schedule ADU and addition work across the entire city, from the flatter lots west of Harbor Boulevard to the hillside properties near Coyote Hills. Here are a few of the Fullerton neighborhoods we’re in regularly:
- Raymond Hills
- Sunny Hills
- Golden Hills
- Jacaranda
- Fullerton Creek
For estimates, we typically schedule within a few business days and confirm the exact visit window the day before. A written price follows the site walk.
Service Area – Cities Near Fullerton
Our Fullerton crews also serve the surrounding north Orange County cities when schedules allow. If you’re in Placentia, CA, Brea, CA, Yorba Linda, CA, or La Habra, CA, we can send the same Threshold Verified team to your property. Scheduling is coordinated from our Los Angeles office; crews live and work locally across this part of Orange County.
Serving Fullerton, CA - Our Local Coverage Area
We’re based in the Fullerton area and know this community well. Use the map below to see our service coverage - if you’re nearby, we can almost certainly help.
FAQs About ADU Company in Fullerton
Most Fullerton estimate visits are scheduled within two to four business days. We confirm the exact window the day before and send you the name and photo of the technician who will arrive. Call (472) 248-8213 to get on the schedule.
Yes. We prepare the full permit set, submit it to the City of Fullerton, and manage the review cycle through approval. If your neighborhood has an HOA with architectural review, we supply the drawings and documentation they request. You aren’t left to chase the city on your own.
Many Fullerton homes built before 1970 still run a 100-amp panel, and a detached ADU with its own kitchen and HVAC often requires 200-amp service. We factor this into the written quote up front, so it doesn’t arrive later as a surprise line item.
Call (472) 248-8213 to schedule your free estimate, and we’ll walk your Fullerton lot before we put a single number in writing.
What happens when you call
- 1A real person answersNo phone trees - talk to a local adu pro.
- 2You get an upfront price rangeHonest numbers before anyone is dispatched. No surprises.
- 3We come out and measureLicensed & insured, at a time that suits you - the visit and the quote are both free.
- 4You get the price in writingLine-itemed, yours to keep, and nothing starts until you say go.
What Fullerton Customers Say
"Itemized estimate with allowances laid out. Final cost was within a hair of the quote."
- Naomi R."Backyard ADU for my mother. The project manager showed ID and walked me through the permit steps, the foundation plan, and the schedule. Moved her in on time."
- Margaret C."Insulated the walls and ceiling properly. It stays comfortable even in July."
- Tamika W.
