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Get your free estimateHow Much Does Junior ADU & Interior Conversion Cost in San Francisco?
In San Francisco, a junior accessory dwelling unit (JADU) conversion typically runs $90,000 to $180,000 when built inside an existing home footprint, like a converted garage, basement, or attached bonus room. A full interior conversion that adds a kitchenette, bathroom, and separate entrance lands closer to $190,000 to $320,000 depending on foundation work, plumbing runs, and finish level. These are real 2026 numbers for the San Francisco market, where permit fees, seismic requirements, and labor rates push costs well above the state average.
We’re Lodgewick ADU San Francisco, part of the Kingswell family of home-service companies. Russ Delmar leads our San Francisco team, and we’ve been building JADUs and interior conversions in this city long enough to know exactly where the money goes. This guide breaks down every line item so you can plan with a real number, not a guess.
Junior ADU & Interior Conversion Cost Breakdown (2026)
Here’s what a JADU or interior conversion actually costs in San Francisco right now. These ranges reflect what we’ve quoted on projects from the Outer Sunset to Bernal Heights over the past 18 months.
| Cost Category | Typical Range (San Francisco, 2026) | What It Covers |
|---|---|---|
| Permits & plan check | $6,000 – $14,000 | San Francisco DBI building permit, planning review, school fees, sewer connection review |
| Design & engineering | $8,000 – $22,000 | As-built drawings, structural calculations, Title 24 energy compliance, any seismic retrofit plans |
| Demolition & site prep | $4,000 – $12,000 | Removing garage doors, interior walls, old flooring, and any drywall with lead paint or asbestos (common in pre-1978 homes) |
| Plumbing rough-in & fixtures | $12,000 – $28,000 | New bathroom, kitchenette sink, water heater tie-in or tankless unit, drain lines to the main sewer lateral |
| Electrical rough-in & panel | $8,000 – $20,000 | Subpanel, wiring for kitchenette and bathroom, lighting, GFCI circuits, smoke/CO detectors per San Francisco code |
| Foundation & seismic work | $5,000 – $40,000 | Garage slabs often need raising, moisture barriers, and bolting. Hillside lots in Noe Valley or Diamond Heights can require significant retaining work |
| Framing, drywall & insulation | $10,000 – $25,000 | Wall framing, ceiling work, R-19 or better insulation, sound insulation for shared walls |
| Flooring, tile & finishes | $8,000 – $22,000 | LVP or engineered wood, bathroom tile, kitchenette countertops, baseboards, paint |
| Kitchenette build-out | $6,000 – $18,000 | Compact refrigerator, sink, two-burner cooktop (no oven required for JADUs), cabinetry, countertop |
| Bathroom build-out | $12,000 – $28,000 | Shower or tub-shower, toilet, sink vanity, exhaust fan, waterproofing |
| HVAC / ventilation | $4,000 – $12,000 | Ductless mini-split or tie-in to existing forced air, bathroom exhaust, kitchenette venting. San Francisco’s fog-heavy microclimates make moisture control a real issue in Sunset and Richmond District conversions |
| Windows & exterior door | $5,000 – $15,000 | Egress windows, separate entrance door (required for a true JADU), weather sealing |
| General contractor fees & project management | $12,000 – $30,000 | Project oversight, scheduling, site management, the 10-15% margin every honest contractor charges |
Total realistic range for a San Francisco JADU or interior conversion: $90,000 at the low end for a simple, already-permitted space, up to $320,000 for a full gut-and-rebuild with seismic work on a hillside lot.
The biggest cost drivers aren’t cosmetic. In San Francisco they’re seismic, sewer, and stairs. Old garage slabs sit directly on dirt, which means moisture intrusion unless you add a moisture barrier and sometimes a raised floor system. San Francisco DBI also requires that any conversion with a sleeping area include a compliant egress window or door, and many pre-1950 garages don’t have that. And if your sewer lateral runs under the slab, you’re often looking at a full replacement to meet current code before the conversion can be signed off.
What Affects Junior ADU & Interior Conversion Pricing in San Francisco
- Seismic requirements. San Francisco sits in Seismic Design Category D or E, meaning any structural change triggers sheer wall and bolting requirements. A garage conversion in the Richmond District with a soft-story condition can add $10,000 to $40,000 in retrofitting before you ever pick out a tile color.
- Permit timeline and planning review. San Francisco’s Department of Building Inspection is faster than it was five years ago, but plan check for ADUs still takes 4 to 10 weeks on average. A stalled permit means carrying costs and, for some homeowners, an extra month or two of mortgage interest on unused equity.
- Existing plumbing and sewer condition. Homes in the Outer Sunset and Parkside built before 1960 often have clay sewer laterals that are cracked or root-bound. If the conversion adds a bathroom, the city will require the lateral to pass a video inspection. A lateral replacement runs $6,000 to $18,000 in San Francisco.
- Finish level. A JADU with a prefab shower pan, LVP flooring, and stock cabinetry can move in for under $150,000 all-in. The same floor plan with a custom tile shower, heated floors, and solid-surface counters pushes well past $200,000. We work with brands like James Hardie for siding and trim, and we spec materials from established ADU prefab manufacturers when the layout allows for it.
- Hillside and foundation conditions. Lots in Noe Valley, Glen Park, and the slopes of Twin Peaks frequently require retaining walls, pier work, or shoring during excavation. These costs are often invisible until demo starts, which is why we always do a foundation walk-through before the written quote goes out.
- Access to the work site. San Francisco’s tight lots mean narrow stairwells, shared driveways, and limited street parking for crews. If we can’t get a dumpster or a materials lift in place, labor costs rise because everything moves by hand. It’s one of the reasons San Francisco conversions run 20-30% above comparable work in Sacramento or San Jose.
Junior ADU vs. Full ADU: What’s the Price Difference in San Francisco?
A junior ADU is the most accessible path to rental income or a family suite because it works within the existing footprint of your house. That’s why the cost range is lower than a detached unit. Here’s how the numbers compare in 2026:
- JADU (inside existing home): $90,000 – $180,000. No new foundation, usually no new sewer lateral, and the permit path is simpler because the square footage already exists within the envelope of the home.
- Attached conversion ADU (garage or basement with separate entrance): $140,000 – $260,000. Adds the costs of a separate water heater, subpanel, egress, and sometimes interior stair access.
- Detached new-construction ADU: $300,000 – $550,000 in San Francisco. New foundation, full utility trenching, and the cost of construction labor at current San Francisco rates, which hover around $350 to $500 per square foot for a finished ADU.
For most San Francisco homeowners, starting with a JADU or interior conversion is the highest-return move. The city waives impact fees for units under 500 square feet, and you avoid the expense of a new foundation. That’s real money: a detached ADU foundation alone runs $25,000 to $60,000 on San Francisco soil.
How to Save on Junior ADU & Interior Conversion
- Get a written price before you sign anything. We put every estimate in writing before any work starts. That’s the Kingswell Guarantee, and it’s the single best protection against the price switches that plague this industry. If it’s in the quote, it’s the price. No door-step changes, no surprise line items appearing on week three.
- Choose the right square footage for your permit path. San Francisco allows JADUs up to 500 square feet. Staying under that threshold avoids certain impact fees and shortens plan check. Sometimes 10 fewer square feet means $4,000 to $8,000 less in city costs.
- Keep the bathroom against an existing wet wall. If you can place the new bath adjacent to your current kitchen or bathroom plumbing, you’ll save $5,000 to $12,000 in drain and venting work. Every foot of new drain line run through a slab costs money.
- Consider prefab building components. We work with leading prefab ADU brands and materials suppliers like Abodu, Cover, Dvele, Mighty Buildings, Boxabl, Plant Prefab, Tuff Shed, and James Hardie. On interior conversions, prefab bathroom pods and kitchenette modules can shave 2 to 4 weeks off the schedule and reduce labor costs by 10-15%. Prefab isn’t cheap, but on San Francisco timelines, speed is money.
- Lock in a contractor who actually shows up. A contractor who doesn’t return calls costs you in carrying costs and lost rent. Call us at (707) 760-0502 for a free estimate. A live person answers, 24/7. We’ll schedule a site walk, measure, and deliver a written price with a project timeline.
San Francisco JADU Permit Requirements and How They Affect Cost
San Francisco’s junior ADU rules are defined in the city’s planning code and are more generous than most California jurisdictions. A JADU can be up to 500 square feet inside an existing single-family home. It needs a separate entrance, a kitchenette (efficiency kitchen with a sink and cooking appliance, but no requirement for a full oven), and either a separate bathroom or shared access to one within the dwelling.
Practically, what matters for your budget: the San Francisco DBI will require structural calculations whenever a load-bearing wall is moved or a garage opening is infilled. That means an engineer’s stamp, which adds $2,000 to $6,000 to the design line item. You’ll also need Title 24 energy compliance, which in practice means certain insulation minimums and window ratings. And if the conversion creates a new sleeping room, you’ll need hard-wired smoke detectors interconnected with the rest of the house and an emergency escape opening sized to code.
These are the same requirements any reputable San Francisco contractor handles every week. When we quote a project, the permit fees, engineering, and energy compliance are line items in the written price. Nothing is estimated loosely and nothing gets billed as a surprise later.
What the Kingswell Guarantee Means for Your JADU Budget
Here’s the thing most homeowners learn the hard way: the lowest bid is rarely the cheapest build. A contractor who underbids will either walk off the job, charge change orders every week, or deliver work that fails inside a year.
We operate under The Kingswell Way, and it applies to every JADU and interior conversion we build in San Francisco:
- Written price first. Before a single nail is driven, you have a detailed itemized price in writing. That’s the number. It doesn’t change at the door.
- Real arrival window. We give you a defined arrival window and we show up in it. Not “sometime this week.” A window you can plan around.
- Clean job site. We leave the work area cleaner than we found it, every day. No debris piles in your driveway, no tools scattered across your yard.
- 365-Day Done Right Promise. Every project includes a written guarantee. If the work isn’t right, we come back and make it right within the guarantee period. That promise is in writing, on your project, before work begins. No fine print, no phone-tag.
Russ Delmar has run Lodgewick ADU San Francisco under this standard since the Kingswell family started the ADU division in 2010. That’s 15 years of San Francisco builds, and every one of them came with a written guarantee.
Junior ADU & Interior Conversion Timeline in San Francisco and What It Costs in Real Terms
Time is money, and in San Francisco, the timeline is often the budget’s quietest line item. Here’s what a typical interior conversion or JADU looks like from the day you call to the day you move in:
- Site walk and written estimate: 1 to 2 weeks. We schedule the walk, measure the space, check the foundation and plumbing access, and deliver a written price. Free, no obligation.
- Design and engineering: 3 to 6 weeks. As-builts, structural calculations, Title 24 compliance, and permit drawings. This phase costs $8,000 to $22,000 and is where many projects get their cost overruns, because low-bid contractors skip the engineering and then discover structural issues during demo. We don’t skip it.
- San Francisco DBI plan check: 4 to 10 weeks. The city has improved ADU review times, but plan check for any conversion touching structural or plumbing still takes a couple months. You can’t speed this up, but a complete permit set keeps you out of the resubmission loop.
- Construction: 10 to 18 weeks depending on scope. A simple interior conversion with no foundation work can be done in 10 to 12 weeks. A garage conversion with slab work, seismic bolting, and a full bath runs 14 to 18 weeks.
A delay of two months in plan check or construction means two months of lost rent or two months without the space you’re paying for. At San Francisco rental rates for a 1-bedroom JADU, which run $1,800 to $2,600 per month, a two-month delay is $3,600 to $5,200 in real money. That’s why we spec materials early, order fixtures the week the permit is submitted, and stage the work so no trade sits idle.
FAQs – Junior ADU & Interior Conversion Cost
How much does a junior ADU cost in San Francisco?
A junior ADU in San Francisco costs $90,000 to $180,000 for a conversion inside an existing home footprint, with most projects landing around $130,000 to $160,000. The range reflects whether you need seismic work, a sewer lateral replacement, or a new electrical subpanel. Call (707) 760-0502 for an exact quote. Estimates are free and the price we quote is the price you get, in writing.
Is it cheaper to convert a garage or build a new ADU in San Francisco?
Converting a garage is $90,000 to $260,000 in San Francisco, while building a new detached ADU runs $300,000 to $550,000. The conversion is cheaper because the foundation, roof, and three of four walls already exist. The tradeoff is ceiling height and sometimes the need to raise the slab, but even with slab work, a conversion usually comes in at half the cost of new construction.
How long does a junior ADU conversion take in San Francisco?
Plan on 4 to 6 months from first call to move-in for a typical San Francisco JADU conversion: 1 to 2 weeks for estimate and scope, 3 to 6 weeks for design and engineering, 4 to 10 weeks for DBI plan check, and 10 to 14 weeks of construction. Prefab components from brands like Cover or Boxabl can cut 2 to 4 weeks off the construction phase.
Do I need a permit for an interior conversion in San Francisco?
Yes. Any San Francisco conversion that adds plumbing, moves walls, or creates a new dwelling unit requires a DBI permit and, for JADUs, planning review. Unpermitted work won’t pass a resale inspection, and San Francisco is aggressive about flagging unpermitted ADUs in property records. The permit line item is $6,000 to $14,000, and skipping it will cost you far more when you sell or refinance.
What’s the cheapest way to add a junior ADU in San Francisco?
The most cost-effective JADU in San Francisco is a bedroom-to-efficiency conversion that keeps the existing bathroom shared, adds a kitchenette along the current wet wall, and stays under 500 square feet to avoid impact fees. That path can come in around $90,000 to $120,000. The moment you add a dedicated bathroom, a separate entrance, or slab work, you’re looking at $140,000 and up.
Can Lodgewick fix a JADU that another contractor built wrong?
Yes. We regularly take over San Francisco JADU projects where another contractor left the job unfinished or delivered work that failed inspection. The process starts with a site walk and a written assessment of what’s needed to bring the work to code. The same Kingswell Guarantee applies: written price first, real arrival window, clean job site, and a written guarantee on everything we touch.
Get a Written Price for Your San Francisco JADU or Interior Conversion
You deserve a real number before you commit to anything. That’s how we’ve operated since 2010, and it’s why homeowners across San Francisco, from the Mission to the Outer Richmond to Visitacion Valley, call Lodgewick first when they’re ready to convert a garage, basement, or interior space into a junior ADU. Our home page has the full picture of what we do, and our Junior ADU & Interior Conversion in San Francisco page covers the build process in detail.
Call us at (707) 760-0502. A live person answers, 24/7. We’ll schedule a free site walk, measure the space, and deliver a written price with a project timeline, the 365-Day Done Right Promise in writing, and no surprises down the line. That’s the Kingswell Guarantee.
Pricing reflects the San Francisco market as of 2026. Lodgewick ADU San Francisco offers free estimates – call (707) 760-0502.
Written by Russ Delmar, Owner at Lodgewick ADU San Francisco, serving San Francisco since 2010.
What Our Customers Say
"The ADU came out beautiful and the permitting, which terrified me, was handled start to finish. They kept me updated every week so I was never wondering what was happening."
- Shauna Mills"Turned our detached garage into a little guest house. Clean crew, respectful of the neighbors, and no mystery charges at the end. Love how it turned out."
- Carmela Fontes"I was nervous about adding on but they walked me through every step and every cost before we started. No surprise change orders halfway through like I'd heard horror stories about."
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