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Wood framing and electrical rough-in during ADU construction in the San Francisco Bay Area

ADU Construction — Add Space, Value & Income to Your Property

California's ADU laws have made it easier than ever to build a backyard unit. But easier doesn't mean easy. You need a contractor who's navigated the permit process in your city — not one figuring it out on your project.

Or call (650) 771-5817
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More Space. More Value. More Possibilities.

Maybe you need space for aging parents. Maybe you want rental income to offset your mortgage. Maybe your adult kid needs a place while they get on their feet. Or maybe you just want to add $200,000+ to your property value. Whatever the reason, an Accessory Dwelling Unit is one of the smartest investments a Bay Area homeowner can make right now.

California's ADU laws (AB 881, SB 13, AB 68) have dramatically simplified the approval process statewide. But every city interprets these laws slightly differently. SF's DBI, Oakland's Planning & Building, Marin's Community Development, and each Peninsula and South Bay jurisdiction have their own review processes, timelines, and quirks. The paperwork alone stops most homeowners in their tracks.

Gadget Construction is the builder side of your ADU project. You bring the plans from your architect or designer; we take it from there — constructability review, detailed estimate, permit submittal and plan check support, full construction, and final inspections. We've built detached backyard units, garage conversions, and basement ADUs across 31 Bay Area cities in 6 counties. We know what each building department is looking for, which design choices get flagged in plan check, and how to avoid the common mistakes that add months and thousands of dollars to ADU projects.

Our ADU Construction Services

Full-service ADU design and build — we manage every phase so you get a finished, permitted unit without the chaos.

Detached Backyard ADUs

New standalone structures built in your backyard — from studio apartments to full 2-bedroom units up to 1,200 sq ft.

Garage Conversions

Transform your existing garage into a finished living space — often the fastest and most cost-effective ADU option.

Basement Conversions

Convert unused basement space into a legal, permitted dwelling unit with proper egress, ventilation, and waterproofing.

Junior ADUs (JADUs)

Up to 500 sq ft carved out of your existing home — an efficient option when lot space is limited.

Permit & Plan Check Support

Bring us your approved plans. We submit to your local building department, track the review, and respond to plan check corrections so your project keeps moving.

ADU Costs in the Bay Area

Garage Conversion

Existing structure to finished unit

$100,000–$200,000

Junior ADU (within home)

Up to 500 sq ft

$80,000–$150,000

Detached ADU (studio/1BR)

New construction

$200,000–$350,000

Detached ADU (2BR, high-end)

Full design-build

$300,000–$450,000+

Basement Conversion

Including waterproofing and egress

$120,000–$250,000

Prices reflect typical San Francisco market rates. Your exact cost depends on scope, site conditions, materials, and permits. We provide detailed, itemized estimates — no ballpark guesses.

Get Your Exact Price — Free Estimate

Our Process

Our ADU Process

1

Free Consultation & Feasibility Walk

Already have an architect or designer? Bring them in. We walk your lot, review setbacks, height limits, and utility access, and tell you what's realistically buildable before you spend money on plans.

2

Plan Review & Detailed Estimate

You bring the approved plans from your architect or designer. We review them for constructability, flag anything that will trip up plan check, and deliver a line-item estimate — no vague allowances, no surprise change orders.

3

Permit Submittal & Plan Check Support

We submit your plans to your local building department, track the review, respond to corrections, and coordinate revisions with your designer. We've shepherded ADU permits through 31 Bay Area cities — we know what each jurisdiction asks for.

4

Construction

Foundation, framing, plumbing, electrical, HVAC, finishes — built by our crew with weekly photo updates and one point of contact from groundbreak to final walkthrough.

5

Final Inspections & Certificate of Occupancy

We coordinate every city inspection through final sign-off. You get a fully permitted, legal dwelling unit ready for move-in or rental.

Why Choose Gadget Construction

Multi-Jurisdiction Permit Experts

We've navigated the ADU permit process in cities across 6 Bay Area counties. We know what each building department wants and how to deliver it without delays.

We Work With Your Designer

Already have plans or an architect on board? Perfect. We slot in as your builder, review for constructability, and coordinate directly with your design team through permitting and construction.

Value-Engineered

We design for maximum livability and property value without over-building. Smart investments, not vanity projects.

Fully Permitted & Legal

Every ADU we build is fully permitted with a Certificate of Occupancy. No gray areas, no surprises at tax time.

Our ADU Projects

Backyard Studio ADU — ADU project in Berkeley by Gadget Construction

Backyard Studio ADU

Berkeley

Two-Story ADU — Framing Phase — ADU project in Bay Area by Gadget Construction

Two-Story ADU — Framing Phase

Bay Area

Two-Bedroom Detached ADU — ADU project in San Rafael by Gadget Construction

Two-Bedroom Detached ADU

San Rafael

See More of Our Work

Frequently Asked Questions

Under current California law, you can build a detached ADU up to 1,200 sq ft on most single-family lots, regardless of lot size or existing FAR. Junior ADUs (JADUs) can be up to 500 sq ft within your existing home. In many cases, you can build both a JADU and a detached ADU on the same lot. Setback and height requirements vary by city — we assess your specific lot and local rules during the feasibility visit.
Yes. ADUs can be rented out as long-term rentals across the Bay Area. Market rates for a 1-bedroom ADU range from $1,800 to $3,500+/month depending on city, location, size, and finishes. Note: some cities like SF have additional rent control and just-cause eviction protections for ADUs. We recommend consulting a property management professional for your city's current rental regulations.
No. California law eliminates the parking requirement for ADUs in most cases, including when the ADU is within half a mile of public transit. Even if you convert your garage to an ADU, you are not required to replace the lost parking. This applies across all Bay Area cities.
Yes. Studies show that a permitted ADU typically adds $200,000–$400,000+ to property value in the Bay Area market — often exceeding the construction cost. The rental income stream also improves your property's investment profile. A fully permitted, well-built ADU is one of the best ROI home improvements you can make in the current market.
ADU costs across the Bay Area typically range from $150,000 to $400,000+ depending on type, size, finishes, and location. Garage conversions start around $100,000–$200,000. Detached new-construction ADUs run $250,000–$400,000+ for a fully finished unit. Costs include design, engineering, permits, site work, construction, and finishes. We provide detailed estimates with line-item breakdowns.
Once you have approved plans from your architect or designer, our side of the timeline is typically 6–12 months: permit review (2–4 months depending on the city) plus construction (4–8 months depending on type and size). Garage conversions are on the faster end; new detached construction takes longer. Some jurisdictions like Oakland and Berkeley have expedited ADU review. If you don't have plans yet, add 1–3 months on the front end for design with your architect. We give you a city-specific timeline at the estimate phase.

Thinking About an ADU?

Start with a free feasibility assessment. We'll evaluate your lot, walk you through your options, and tell you exactly what's possible — and what it will cost.

Or call (650) 771-5817 — talk to a real person, not a call center.
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