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Get your free estimateHow Much Does Junior ADU & Interior Conversion Cost in Long Beach?
A junior ADU (JADU) or interior conversion in Long Beach typically costs between $85,000 and $165,000 in 2026, with most homeowners landing around $120,000 for a fully permitted conversion of an existing attached space like a garage, basement, or bonus room. Interior conversions that repurpose already-finished square footage run lower, starting near $60,000, while detached new-construction junior units with a kitchenette and separate entrance push toward the top of that range. These figures reflect Long Beach’s current permit fees, labor rates, and the finish levels most families choose when they’re planning a unit that will actually be lived in, not just roughed in.
Before we get into the line items, know this: every project we price at Seedling ADU Long Beach comes with a written number before a single tool is picked up. No allowances that balloon. No change orders that surprise you at the final walkthrough. You’ll know the price, the scope, and the schedule before we start.
Key Takeaways
- Typical range: $85,000 – $165,000 for a permitted junior ADU or interior conversion in Long Beach; $60,000 – $85,000 for simpler conversions of already-conditioned space.
- Per square foot: $220 – $380 for interior conversions; prefab junior units from brands like Abodu and Boxabl can bring costs to $180 – $260 per square foot for the structure alone.
- Biggest cost drivers: whether the space already has plumbing, the condition of the existing foundation or slab, and whether you’re adding a full kitchen versus a kitchenette.
- Long Beach specifics: City permit fees for ADUs and JADUs run $2,500 – $6,000 depending on scope, and seismic retrofit requirements in older homes (pre-1970) can add $8,000 – $20,000.
- Timeline: Interior conversions take 10 – 16 weeks from permit submission to final inspection; detached prefab JADUs can be set in 4 – 6 weeks after site prep.
Junior ADU & Interior Conversion Cost Breakdown (2026)
Here’s what a junior ADU or interior conversion in Long Beach costs when you break it into real line items. These are the numbers we see across Belmont Shore, Bixby Knolls, Naples, Alamitos Beach, and the Wrigley neighborhood. They’re not national averages pulled from a cost calculator. They reflect what Long Beach inspectors require, what Long Beach subcontractors charge, and what local material costs look like right now.
| Cost Component | Typical Range (Long Beach, 2026) | What It Includes |
|---|---|---|
| Design & Engineering | $6,000 – $14,000 | Architectural drawings, structural engineering, Title 24 energy calculations, and any revisions required by the city during plan check. |
| City Permits & Fees | $2,500 – $6,000 | Building permit, electrical, plumbing, mechanical, and Long Beach’s ADU-specific fees. Sewer capacity fees can add $1,500 – $3,000 if the unit ties into the main line. |
| Demolition & Site Prep | $3,000 – $10,000 | Removing existing garage walls or interior partitions, hauling debris, and preparing the slab or subfloor. Includes any asbestos or lead testing required for pre-1978 homes, which is common in Long Beach’s older housing stock. |
| Foundation / Slab Work | $4,000 – $22,000 | If the existing slab is sound, you’re near the low end. If it’s cracked or unpermitted work from a previous owner needs remediation, costs climb. Post-tension slab work in Naples or the Peninsula adds more. |
| Framing & Structural | $8,000 – $25,000 | New interior walls, headers for new windows or doors, seismic bracing where required. Long Beach’s retrofit ordinance applies to many pre-1970 structures, even for interior conversions. |
| Plumbing | $12,000 – $28,000 | Bathroom rough-in, kitchenette or kitchen sink, water heater, and drainage lines. If the conversion area sits far from the main sewer line, expect the higher end. |
| Electrical | $8,000 – $18,000 | New subpanel, wiring for the unit, lighting, outlets, and a separate meter if the city requires it. Long Beach building code now requires EV-ready capability in new garage conversions under certain conditions. |
| HVAC | $6,000 – $14,000 | Mini-split heat pump system is standard for JADUs. A ducted system tied to the main house is rarely worth it for a unit under 500 square feet. |
| Insulation & Drywall | $5,000 – $12,000 | R-13 to R-21 wall insulation, attic insulation if applicable, drywall, tape, and texture. Sound insulation between the unit and the main house is worth specifying up front. |
| Flooring | $3,500 – $9,000 | LVP, engineered hardwood, or tile for a 300 – 500 square foot unit. Materials and labor included. Families with pets often choose LVP for durability. |
| Kitchenette / Kitchen | $6,000 – $30,000 | A junior ADU requires only a kitchenette (sink, small fridge, microwave, counter) by California law. A full kitchen with a stove, oven, and dishwasher pushes costs up. The gap between a $6,000 kitchenette and a $30,000 full kitchen is one of the biggest pricing swings we see. |
| Bathroom | $10,000 – $22,000 | Full bathroom with shower, toilet, vanity, and tile. A tub adds $2,000 – $4,000. Waterproofing and pan work done to Long Beach inspection standards. |
| Doors & Windows | $3,000 – $9,000 | Exterior door for separate entrance (required for JADUs), interior doors, and egress windows if the bedroom needs them. |
| Finishes & Fixtures | $4,000 – $12,000 | Light fixtures, plumbing fixtures, cabinet hardware, paint, and trim. This is the easiest place to overspend, which is why we write every allowance down before starting. |
| Exterior Work (if applicable) | $2,000 – $15,000 | Siding repair, stucco patch, or the facade work needed to make a garage conversion look like it was always part of the house. This line item surprises people, which is exactly why we include it in every written price. |
What moves you toward the bottom or top of those ranges? The condition of what’s already there. A 1940s garage in Rose Park with an intact perimeter foundation, a nearby sewer line, and a subpanel with spare capacity is a $95,000 project. The same garage with a cracked slab, no sewer within 40 feet, and a 60-amp panel that needs complete replacement becomes a $140,000 project. Neither number is wrong. Both are knowable before we start.
Junior ADU vs. Interior Conversion: What’s the Difference in Cost?
In Long Beach, “Junior ADU” and “interior conversion” get used interchangeably, but the state defines them differently, and the distinction affects your budget. A junior ADU is legally limited to 500 square feet, must be created within the existing walls of a single-family home (or an attached garage), and requires only a kitchenette, not a full kitchen. It can share a bathroom with the main house, though most Long Beach families building one for a parent or a rental tenant include a private bath.
An interior conversion is broader: any existing finished or semi-finished space converted to a dwelling unit. A converted garage with its own entrance is a conversion. A finished basement turned into a studio is a conversion. A bonus room above the garage with a bath and kitchenette added is a conversion.
The cost difference comes down to what’s already there. If the space has drywall, electrical, and a floor, you’re paying $180 – $260 per square foot to convert it. If it’s raw garage space with exposed studs and a bare slab, you’re paying $260 – $380 per square foot to bring it up to living standard. A 400-square-foot JADU in a finished bonus room might run $75,000. The same 400 square feet as an unfinished attached garage might run $125,000.
We price both the same way: we walk the space, we measure, we write a number, and you see it before you commit to anything.
What Affects Junior ADU & Interior Conversion Pricing in Long Beach
- Plumbing access is the single biggest variable. If the space sits above or adjacent to existing drain lines, the plumbing rough-in stays under $15,000. If we’re running a new drain across a slab or under a finished floor to reach the main sewer stack, that line item can hit $28,000. Homes in the Craftsman-heavy neighborhoods around Rose Park and Bluff Heights often have cast-iron lines from the 1920s that are still functional, but the access points are rarely where you want them.
- The condition of the existing foundation or slab. Long Beach sits on sandy, liquefaction-prone soil near the coast. Older slabs in Alamitos Beach and the Peninsula crack differently than slabs inland in Bixby Knolls. If an engineer signs off on the existing slab as-is, you save thousands. If it needs grinding, leveling, or partial replacement, that’s a real cost we’ll show you in the written price before anyone starts.
- Whether the space is currently conditioned. A bonus room with insulation and HVAC ducting already in the walls is a different project than a bare garage. Conditioned space converts faster and cheaper because the thermal envelope is partly there. Unconditioned space needs insulation, drywall, HVAC, and often more substantial window and door upgrades.
- Parking replacement requirements. California law says a city can’t require parking replacement for an ADU when the existing garage is converted, but Long Beach still has specific rules about curb cuts, driveway widths, and front-yard parking. In neighborhoods like Belmont Heights where street parking is tight, some homeowners add a side-yard parking pad, which adds $4,000 – $10,000 to the project. We’ll tell you what the city will actually require before you spend money on drawings.
- Seismic retrofit scope on older homes. Long Beach building code requires seismic evaluation for many pre-1970 structures when you’re changing occupancy or adding load. A simple brace-and-bolt retrofit runs $4,000 – $8,000. Full shear-wall reinforcement or foundation bolting on a larger older home can run $12,000 – $20,000. This is not optional if the engineer flags it, and we include it in the written price from day one.
- Finish level: kitchenette versus full kitchen, tile versus acrylic shower, LVP versus hardwood. These choices swing the final number by $15,000 – $30,000 on a typical 400-square-foot unit. We walk every homeowner through the actual cost of each choice, not in the abstract, but in the context of their specific floor plan and how they plan to use the unit.
How Long Does a Junior ADU or Interior Conversion Take in Long Beach?
Plan on 10 to 16 weeks for a typical interior conversion, from the day we submit plans to the city through final inspection. Long Beach’s plan check turnaround for JADUs and interior conversions is running 4 – 8 weeks right now, which is faster than the 9 – 14 weeks we saw in 2023, but still slower than homeowners expect. The construction itself is usually 6 – 10 weeks for a conversion of existing space. Prefab and modular junior units from brands like Abodu and Mighty Buildings can compress the on-site construction window to 4 – 6 weeks once the foundation and utility connections are ready.
We work with families in Lakewood Village and El Dorado Park whose kids are still napping in the main house during construction. The crew runs quiet tools before 9 a.m. where possible, the work area is sealed off from the rest of the home, and a photo of the clean-up is sent before the crew leaves each day. That’s the Cedarwell Care Promise, and it’s not an upsell. It’s how every Seedling job runs.
Prefab Junior ADUs: A Different Price Path
Some Long Beach homeowners go a different route: a prefabricated junior ADU from a company like Abodu, Cover, Boxabl, or Mighty Buildings. These units are built in a factory, trucked to the lot, and set on a prepared foundation. The structural shell costs $50,000 – $90,000 depending on size and finishes, which is often less per square foot than site-built. But the total project still requires site work, foundation, utility connections, and permits, which run $35,000 – $60,000 in Long Beach. Total: $85,000 – $150,000, which lands in the same range as a conventional site-built conversion.
Ben Ortega, who leads Seedling ADU Long Beach, has walked more than a hundred Long Beach lots with families weighing this exact decision. “Prefab isn’t automatically cheaper, and site-built isn’t automatically better. The right choice depends on access to the lot, the condition of the utilities, and how custom the space needs to be. We price both options, in writing, and let the family decide.”
Seedling works directly with Abodu, Cover, Dvele, Mighty Buildings, Boxabl, Plant Prefab, Tuff Shed, and James Hardie materials. That’s not a list we put on the website because it looks good. It’s a list we put there because we’ve installed or specified each one, and we can tell you which one makes sense for a Long Beach lot, a Long Beach inspector, and your budget.
How to Save on Junior ADU & Interior Conversion
The honest way to save money on a junior ADU or interior conversion in Long Beach isn’t to cut corners. It’s to make decisions before construction starts and to avoid changing your mind after the drywall goes up. Here’s what actually keeps the number down:
- Choose a kitchenette, not a full kitchen, if the unit is for a family member. A JADU legally requires only a kitchenette: sink, small refrigerator, microwave, and counter. Going this route saves $10,000 – $20,000 compared to a full kitchen with a range, hood, and dishwasher. If the unit is for an aging parent who’ll eat most meals in the main house, a kitchenette is the right call on function and budget.
- Convert an already-conditioned space. A bonus room, den, or finished portion of the house that already has insulation, drywall, and HVAC access converts for less than a raw garage. The difference is $60 – $120 per square foot, which on 400 square feet is $24,000 – $48,000.
- Keep the bathroom simple. A standard 5′ x 8′ bathroom with an acrylic or fiberglass shower surround costs $4,000 – $6,000 less than one with a custom tile shower and glass enclosure. The function is identical. The look in a rental or a parent’s unit rarely justifies the difference.
- Decide on finishes before permits are pulled. Every change order after framing costs double what it would have cost at the design table. We write your finish schedule into the original price: exact flooring product, exact tile, exact fixtures. You see the number, you approve it, and nothing changes unless you choose to change it.
- Lock your scope before demolition starts. The most expensive sentence in construction is “while we’re in there, can we also…” If you think you might want something done, tell us during the estimate walkthrough, not after the walls are open. We’d rather give you a number for everything you might want up front than surprise you with a change order later.
We offer free estimates on every junior ADU and interior conversion in Long Beach. Call (562) 362-4592 and we’ll walk the space, talk through what you’re planning, and hand you a written number before you spend a dollar on design work.
Long Beach Permits and Fees: What You’ll Actually Pay
Long Beach’s permit landscape for ADUs and JADUs has shifted since the statewide ADU reforms took effect. The city cannot require parking replacement for a converted garage, cannot charge school impact fees on units under 750 square feet, and must process ADU and JADU applications ministerially, which means no discretionary review hearings. What the city does charge: building permit fees based on valuation, electrical and plumbing permits, mechanical permits, and plan check fees. For a typical 400-square-foot JADU, expect $2,500 – $4,500 in total city fees. For a larger conversion with significant structural work, expect $4,500 – $6,000.
One Long Beach-specific item: if your conversion ties into the city sewer main, you may pay a sewer capacity charge of $1,500 – $3,000. If the home is on septic (common in the eastern edges of the city near El Dorado Park and the Lakewood border), the county health department may require a septic capacity evaluation before permit issuance. We identify these items during our initial walkthrough and include them in the written price. You won’t get a letter from the city asking for money we didn’t tell you about.
For a deeper look at what our Junior ADU & Interior Conversion services in Long Beach include from start to finish, that page walks through the full process, from first measurement to final inspection.
FAQs – Junior ADU & Interior Conversion Cost
How much does a junior ADU cost in Long Beach in 2026?
Expect $85,000 to $165,000 for a complete, permitted junior ADU in Long Beach, depending on whether you’re converting existing conditioned space or building out an unfinished garage. Simple conversions of already-finished rooms run $60,000 – $85,000. Call (562) 362-4592 for a written estimate on your specific space, free of charge.
Is it cheaper to convert a garage or build a detached ADU in Long Beach?
Converting an attached or detached garage is almost always cheaper than building a new detached unit, because the foundation, framing, and roof already exist. A garage conversion typically runs $110,000 – $165,000, while a new detached ADU of similar size runs $180,000 – $280,000. The gap narrows if the garage slab or roof needs major work.
What is the minimum size for a junior ADU in Long Beach?
California law sets the maximum size for a JADU at 500 square feet; there is no statutory minimum, but Long Beach enforces habitability standards that effectively require at least 150 – 220 square feet for a unit with a sleeping area, kitchenette, and either a private or shared bathroom. A 300-square-foot studio JADU typically costs $75,000 – $100,000 to build out.
Do I need a separate entrance for a junior ADU in Long Beach County?
Yes, a junior ADU in Long Beach requires a separate exterior entrance or an entrance through a shared interior space with direct access to the exterior. Adding a new exterior door to a garage or bonus room costs $2,000 – $4,500 including framing, door, hardware, and weatherproofing.
Can you build a junior ADU above a garage in Long Beach?
Yes, a garage-top JADU is allowed in most Long Beach residential zones, and costs $140,000 – $200,000 because it requires structural reinforcement of the existing garage, new stairs or exterior access, and often a new roof assembly. A ground-level conversion is less expensive; we’ll price both options during our estimate.
How fast can you start a junior ADU conversion in Long Beach?
We can start site work 3 – 6 weeks after you approve the written price and the plans are accepted by the city, assuming no major structural surprises. Same-start estimates are free: call (562) 362-4592 and we’ll walk your property within a few days.
Why Written Pricing Matters in Long Beach
Most of the stories we hear from Long Beach families who had a bad ADU experience start the same way: the contractor gave a “rough estimate,” the family signed, and six months later the final bill was 30% over the original number with no explanation beyond “unforeseen conditions.” The unforeseen conditions were foreseeable. A cracked slab is foreseeable if you look at it. A sewer line 60 feet from the unit is foreseeable if you measure it. An electrical panel that’s already full is foreseeable if you open the door.
We don’t do rough estimates. We do written prices. Ben Ortega walks every Long Beach property personally, measures the space, checks the existing conditions, and writes a number that includes everything: permits, materials, labor, finishes, and the contingencies we expect. If something changes, we tell you before it changes the price. That’s not a marketing line. It’s how we’ve always run, because it’s the only way a family can plan a $120,000 project without losing sleep.
What the Crew Leaves Behind: The Cedarwell Care Promise
If you’re building a junior ADU while your family still lives in the main house, the construction process matters as much as the finished unit. We know this because most of our Long Beach clients are adding a unit for a parent who’s moving in, an adult child who’s not leaving, or a tenant who’ll help cover the mortgage. Life doesn’t pause during construction. The baby still naps. The dog still needs to go out. The floors in the main house still matter to you.
Our crews wear shoe covers inside the home, lay down drop cloths on every path from the entrance to the work area, and use pet-safe products wherever there’s a choice. A photo of the clean-up is sent to the homeowner before the crew leaves every single day. It’s not a courtesy. It’s the standard.
And if something isn’t done right, the 365-Day Done Right Promise covers it. In writing, on every project. We come back and we make it right. That covers every ADU, garage conversion, and home addition we build in Long Beach.
Getting Started: Your First Step
If you’re considering a junior ADU or interior conversion in Long Beach, the smartest first step is a free on-site walkthrough. We’ll measure the space, check the existing conditions that drive cost, talk about how you plan to use the unit, and hand you a written price. No design contract required. No money down to get the number. If you decide to move forward, we handle the design, the permits, and the build, and your family lives through the process with shoe covers, drop cloths, and a clean-up photo every day.
Call (562) 362-4592 to schedule your free estimate. A live person answers, 24/7, whether you’re calling during your lunch break or at 9 p.m. after the kids are in bed.
Pricing reflects the Long Beach market as of 2026. Seedling ADU Long Beach offers free estimates – call (562) 362-4592.
Written by Ben Ortega, Owner at Seedling ADU Long Beach, serving Long Beach since 2021.
What Our Customers Say
"Added a backyard cottage. The team protected our existing landscaping and left the yard clean every evening. Gentle, respectful, and they walked us through each stage calmly."
- Tamara Welsh"They converted our garage and were so mindful that we were living right there through it. Quiet hours respected, site swept, nothing left out where the kids play. Lovely work."
- Eugene Park"Junior ADU conversion inside the house. They were incredibly clean about it, plastic walls, floor protection, daily cleanup, all with a toddler in the home. Couldn't have asked for more care."
- Marcus Oyelaran
