ADU in Pomona, CA
Junior ADU and interior conversion in Pomona typically runs $85,000-$155,000 all-in, while site prep and utility work adds $15,000-$45,000 depending on whether your 1940s-1960s tract home needs electrical, plumbing, or foundation upgrades before the city will sign off on a habitability certificate. We’re Ellery ADU Studio, and we’ve designed, permitted, and built more than 900 ADUs since 2015 - every one at a written price before work started, governed by The Haven Standard. Call (909) 506-1121 to schedule your free estimate.
Why Pomona Homes Are Different
Pomona’s residential flats sit on 7,000-10,000 square foot lots, some of the largest in western Los Angeles County, with detached garages that are prime JADU or full ADU conversion candidates. The housing stock runs heavily toward post-WWII wood-frame tract homes and pre-war Craftsman bungalows built between roughly 1920 and 1965, nearly all with detached garages that have undersized 60-amp electrical service, zero insulation, and slab-on-grade floors. Each of those must be remediated to meet Title 24 habitable-space standards before a conversion permit can close.
The climate here is genuinely punishing. Pomona sits in a hot inland valley regularly hitting 105°F+ in summer with almost no marine cooling, meaning HVAC is a code-required baseline, not an upgrade, for any ADU. Mini-split sizing must account for radiant heat load from un-shaded concrete and stucco construction common throughout the city. This meaningfully increases project costs compared to ADUs built in cooler coastal LA cities.
A large share of older residential blocks in Pomona’s central flats were platted with rear service alleys. A converted detached garage ADU can have its own alley-facing entry, separate utility meter location, and even a distinct street address. That layout commands higher rents and simpler tenancy, but requires early coordination with Pomona Building & Safety and the water and power departments on addressing and service separation during permit intake. Layer on Cal Poly Pomona’s 27,000+ students driving year-round rental demand, and the ROI calculation on a garage-to-ADU conversion here becomes more compelling than nearly anywhere else in LA County.
Our Main Pomona Services
Pomona homeowners call us most often for these three services, each with its own dedicated page and pricing.
ADU Design & Permitting in Pomona
We produce the full permit set, structural calculations, and Title 24 energy compliance documentation required by Pomona Building & Safety, then shepherd the plan check through to issuance. Because Pomona’s older garages often trigger fire-separation or setback questions during intake, we front-load those conversations with the city before submittal to avoid the 4-6 week revision cycles that derail timelines. ADU Design & Permitting in Pomona.
Garage Conversion ADU in Pomona
We convert existing detached or attached garages into permitted habitable space, handling slab assessment, insulation, HVAC rough-in, and the electrical service upgrade from 60-amp to 100-amp or 200-amp that Pomona nearly always requires. The alley-access lots common in central Pomona make these conversions particularly attractive for independent tenancy. Garage Conversion ADU in Pomona.
New Detached ADU in Pomona
We design and build standalone ADUs from foundation to final inspection, including coordination with Pomona’s alley-addressing protocols and utility service separation. The large lot sizes here mean many properties can accommodate a full 1,200 square foot detached unit without a variance, though setback and fire-separation rules still govern placement. New Detached ADU in Pomona.
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.
Before
AfterJunior ADU & Interior Conversion in Pomona
Junior ADU and interior conversion in Pomona solves the specific problem of turning underutilized space inside an existing home, or an attached garage, into a permitted rental unit without building new square footage. In a city where 1940s-1960s tract homes dominate and Cal Poly Pomona’s student population keeps rents stable, a JADU or interior conversion lets owners monetize existing structure faster than a ground-up build, though Title 24 HVAC requirements and the need for a separate kitchen and exterior door still demand careful permit planning. We handle Junior ADU & Interior Conversion as a single contract from measured drawings through final inspection.
Room-to-ADU Conversion
Signs you need it
You have a 250+ square foot spare bedroom, den, or attached garage space that shares a wall with your main house and you want to create a separate rental unit with its own kitchen and exterior door.
What it costs in Pomona
Room-to-ADU conversions in Pomona typically run $85,000-$135,000 all-in, with the high end driven by the 100-amp electrical service upgrade and ductless mini-split HVAC that Title 24 and the local climate make mandatory.
How we do it
We measure existing conditions, produce the permit set including fire-separation and sound-transmission details, pull the permit through Pomona Building & Safety, then build out the kitchenette, bath, separate meter or sub-meter, and exterior door with a documented photo record at every visit.
Interior JADU
Signs you need it
You want a smaller, more affordable rental unit, up to 500 square feet, created entirely within your existing home’s footprint without altering the exterior envelope.
What it costs in Pomona
Interior JADUs in Pomona typically range $75,000-$115,000, with savings coming from no foundation work but added costs for the owner-occupancy affidavit filing and the separate kitchen and exterior door that Pomona requires.
How we do it
We verify the 500 square foot maximum against your assessor’s records, design the space plan to include a kitchenette with cooking facilities and a 3/4 bath, prepare the owner-occupancy documentation for Pomona’s Community Development Department, and build to the permitted drawings under our 365-Day Done Right Promise.
What Junior ADU & Interior Conversion Costs in Pomona
| Item | Typical range in Pomona |
|---|---|
| Room-to-ADU conversion (all-in) | $85,000-$135,000 |
| Interior JADU (all-in) | $75,000-$115,000 |
| Electrical service upgrade to 100A | $4,500-$8,500 |
Can a JADU have its own address in Pomona?
Yes, but only if the original structure already has a separate exterior door and the JADU meets Pomona’s separate utility metering requirements; we coordinate this during permit intake with Building & Safety and the utility departments. Call (909) 506-1121 for an exact quote - estimates are free.
Does Pomona require owner occupancy for a JADU?
Yes, California state law and Pomona’s municipal code both require the property owner to live in either the main house or the JADU, and we file the owner-occupancy affidavit as part of your permit set. Call (909) 506-1121 for an exact quote - estimates are free.
ADU Site Prep & Utilities in Pomona
ADU site prep and utilities in Pomona addresses the gap between “I want an ADU” and “the city will let me build one,” a gap that is almost always wider in Pomona than owners expect. The 1940s-1960s tract homes here have 60-amp electrical panels, clay sewer laterals, and uninsulated slab floors that fail Title 24 before a single wall goes up, while the 105°F+ summers make HVAC infrastructure a load calculation problem, not an afterthought. We handle ADU Site Prep & Utilities as a defined scope with a written price, so your conversion or new build isn’t held hostage by surprise underground work.
Electrical Panel Upgrade
Signs you need it
Your existing panel is rated at 60 amps, has no open breaker slots, or still uses a fuse box, any of which will cause Pomona Building & Safety to reject your ADU permit application at intake.
What it costs in Pomona
Electrical panel upgrades in Pomona typically run $4,500-$8,500 for a 200-amp service, with trenching to the alley meter on older central-flat lots adding $2,000-$4,500 if the existing conduit is deteriorated.
How we do it
We pull the load calculation for main house plus ADU, coordinate with Southern California Edison on service lateral sizing, install the new panel with AFCI/GFCI breakers as required by the 2023 NEC, and pass Pomona’s electrical inspection before rough-in begins.
Foundation & Grading
Signs you need it
Your existing garage slab is less than 4 inches thick, cracked with differential settlement, or poured without a vapor barrier, any of which fails the structural and moisture-resistance requirements for habitable space conversion.
What it costs in Pomona
Foundation and grading work in Pomona ranges $12,000-$28,000 for garage slab replacement with proper depth, rebar, and vapor barrier, with expansive soil conditions in the Phillips Ranch area occasionally requiring engineered pier supports.
How we do it
We core-test the existing slab, produce a structural letter if replacement is needed, grade for positive drainage away from the new foundation, pour to 4-inch minimum with #4 rebar at 18 inches on center, and document the vapor barrier installation with photos for your permit closeout.
What ADU Site Prep & Utilities Costs in Pomona
| Item | Typical range in Pomona |
|---|---|
| Electrical panel upgrade (200A) | $4,500-$8,500 |
| Foundation and grading (garage slab replacement) | $12,000-$28,000 |
| Plumbing lateral extension to alley or rear | $3,500-$7,500 |
Does Pomona require a separate water meter for an ADU?
Not for JADUs, but detached ADUs and most garage conversions require separate water service; we coordinate with Golden State Water Company during permit intake to avoid delays. Call (909) 506-1121 for an exact quote - estimates are free.
Can you upgrade utilities without starting the full ADU build?
Yes, we scope and price utility upgrades as standalone work under Haven Standard Clause 1, with the cost credited toward your full construction contract if you proceed within 12 months. Call (909) 506-1121 for an exact quote - estimates are free.
Brands We Service in Pomona
We specify and coordinate prefab and modular systems from Plant Prefab, Tuff Shed, and James Hardie, integrating these into our single-contract design-build workflow so the manufacturer’s warranty and our 365-Day Done Right Promise work together without gaps. We keep common Hardie siding and Tuff Shed hardware in stock locally for faster repair and modification turnaround. See our brands for the full list.
Pricing for ADU in Pomona, CA
| Service | Typical range in Pomona |
|---|---|
| Room-to-ADU conversion | $85,000-$135,000 |
| Interior JADU | $75,000-$115,000 |
| Electrical panel upgrade (200A) | $4,500-$8,500 |
| Foundation and grading | $12,000-$28,000 |
| Plumbing lateral extension | $3,500-$7,500 |
| HVAC mini-split system (ductless) | $6,500-$12,000 |
| Permit set and plan check | $8,500-$15,000 |
| Title 24 energy compliance documentation | $2,500-$4,500 |
What pushes prices up in Pomona: the mandatory HVAC sizing for 105°F+ summer design temperatures, electrical service upgrades from 60-amp legacy panels, and alley-access utility trenching on central-flat lots. What keeps them predictable: Haven Standard Clause 1 locks your written price at signing, with no change orders for scope we’ve already documented.
Neighborhoods We Serve in Pomona
We work across Pomona’s residential neighborhoods, from the historic Craftsman blocks to the post-war tracts, with dispatch and scheduling coordinated from our Los Angeles office and crews serving Pomona locally. Typical response for initial site visits is 2-4 business days.
- Lincoln Park
- Mayfair
- Phillips Ranch
- Westmont
- Arroyo Vista
Service Area - Cities Near Pomona
Our crews work throughout the Pomona Valley and western San Bernardino County, with regular projects in Montclair, CA, Claremont, CA, La Verne, CA, and San Dimas, CA. Each city has its own permit timeline and utility coordination requirements, which we handle as part of the standard scope.
Serving Pomona, CA - Our Local Coverage Area
We’re based in the Pomona 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 in Pomona
Pomona Building & Safety typically takes 8-12 weeks for initial plan check on a complete submittal, with 2-4 week cycles for any corrections; we front-load fire-separation and setback conversations before submittal to minimize revisions.
Yes, but properties in designated historic zones may require additional review by the Historic Preservation Commission for exterior alterations; we flag this during our initial site assessment and adjust the permit timeline accordingly.
California law (AB 670 and SB 896) prohibits HOAs from outright banning ADUs, but some Pomona-area associations still attempt to enforce design guidelines or parking requirements that effectively block projects; we review your CC&Rs during our free estimate and advise on enforceability.
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 Pomona Customers Say
"Handled the whole planning process. We went to one hearing and that was it."
- Rowena C."Garage conversion finished on the drawings and close to the schedule. They were honest that the sewer connection was the unknown, and it was."
- Arjun D."The rental income has covered the payment since the second month. They were realistic about the numbers rather than optimistic."
- Odette N.