ADU builder · Downey, CA
ADU builder in Downey.
Design, permits, financing and construction from one local team. 600+ ADUs delivered across greater LA, including nearby Bellflower, Whittier, Montebello & Long Beach.
Licensed & insured · Construction from $275/sq ft · 5.0★ rated
Building an ADU in Downey
Downey is mostly flat, and many lots have a detached garage or open yard in back, which makes both conversions and new backyard units practical. Owners here build a lot of them: about 239 ADU permits in 2023, about 202 in 2024 and about 244 in 2025, per state housing reports.
ADU Resource Center designs, permits and builds ADUs with one in-house team. Our nearest projects are a single-story ADU in Bellflower, a 450 sq ft unit for an 89-year-old father in Whittier, a 1,200 sq ft ADU in Montebello and a 400 sq ft rental in Long Beach.
You'll have a fixed quote before construction and one project manager from the first plan to final inspection. We can also help you sort out financing.
ADUs in Downey: quick facts
Updated November 2026
- Who issues ADU permits
- City of Downey
- Our construction rates
- $275, $300 or $325 per sq ft (basic, mid-range, luxury); garage conversions $235–$285 per sq ft
- Example cost
- A 600 sq ft one-bedroom runs about $165K–$195K in construction
- Size limits under state law
- Detached ADUs up to 1,200 sq ft on many lots; junior ADUs up to 500 sq ft inside the home
- Permit decision
- State law requires a decision within 60 days of a complete application
- Who builds it
- ADU Resource Center: design, permits and construction by one team, 600+ ADUs delivered, office in Glendale
ADU rules change. We confirm the current rules for your lot on the free consultation.
Real projects nearby
ADUs we've built near Downey.
Hear it from our clients
Homeowners on building their ADU with us
More stories on our testimonials page.
Local know-how
What to know before building in Downey.
Downey handles its own permits
ADU plans go to Downey's Community Development Department and through Building and Safety plan check. We prepare the submittal and the correction responses.
Pre-approved plans need site work
Downey's pre-approved detached ADU plans are a starting point. The city says they're about 80% complete and always need changes for your property, so budget for that design time.
Flat lots keep site costs down
Most Downey lots are level, which avoids grading and retaining walls. Placing the ADU close to existing utilities saves more. Try the cost calculator for a quick estimate.
Garage conversions
A detached garage is often the simplest path to a legal unit here. See garage conversion costs for what drives the price.
What it costs
ADU cost in Downey
We build at a flat rate per square foot: $275 (basic), $300 (mid-range) and $325 (luxury) finishes. Here's what that means for common sizes. Construction only; design, permits and city fees are quoted separately on your consultation.
| ADU size | Basic | Mid-range | Luxury |
|---|---|---|---|
| 400 sq ft studio | ~$110K | ~$120K | ~$130K |
| 600 sq ft 1-bedroom | ~$165K | ~$180K | ~$195K |
| 800 sq ft 2-bedroom | ~$220K | ~$240K | ~$260K |
| 1,000 sq ft 2–3 bedroom | ~$275K | ~$300K | ~$325K |
Get a number for your exact size: ADU cost calculator · Browse ADU floor plans · Converting a garage? See garage conversion cost.
Free consultation
Start your Downey ADU.
Tell us about your property. We'll confirm what's buildable, give you a real price range and walk through financing within 1 business day.
Questions
Downey ADU questions, answered.
Still have a question? Ask us during your free consultation.
Who issues ADU permits in Downey?
Downey is its own city, so ADU plans go to the City of Downey's Community Development Department, with plan check by its Building and Safety Division. We prepare the plans, submit them and handle the corrections until permits are issued.
Does Downey have pre-approved ADU plans?
Yes. Downey runs a pre-approved detached ADU plan program. The city says those plans are only about 80% complete and always need property-specific changes, plus site information. We can work from a pre-approved plan or draw a custom one, and we'll tell you which fits your lot better.
How much does an ADU cost in Downey?
We build at a flat $275, $300 or $325 per sq ft for basic, mid-range or luxury finishes, so a 600 sq ft one-bedroom is about $165K–$195K in construction. Garage conversions run $235–$285 per sq ft. Utility upgrades such as a new electrical panel or sewer work can change the fixed quote.
Can I convert my detached garage in Downey?
Often, yes. A conversion reuses the existing slab, walls and roof, and state law doesn't require new setbacks for the existing structure. An older garage may need a new floor, insulation or electrical before it can be legal living space, and we check that first.
How big can an ADU be on my Downey lot?
State law allows detached ADUs up to 1,200 sq ft on many lots, and a junior ADU up to 500 sq ft inside the house. What fits your lot depends on its size and setbacks under Downey's current rules. We confirm that on the consultation, since ADU rules change.
Free consultation
Ready to build your ADU in Downey?
Tell us about your property and we'll confirm what's buildable, give you a real price range and lay out financing on one free call.
