Mendez & Son's Construction Inc
WHAT TO EXPECT WHEN BUILDING AN ADU IN THE BAY AREA
Building an ADU in the Bay Area is one of the smartest moves a homeowner can make right now. More living space, rental income potential, a place for family — the reasons to build are solid. But before you start calling contractors, you need to understand what the process actually looks like.
FIRST: WHAT IS AN ADU?
An ADU — accessory dwelling unit — is a secondary residential unit built on the same lot as your primary home. It has its own entrance, kitchen, and bathroom. It functions as a fully independent living space.
In the Bay Area, ADUs come in a few forms. Each type has different permit requirements, different cost ranges, and different timelines. Which one is right for your property depends on your lot size, setbacks, existing structures, and what you plan to use the space for.
ADU Construction ServicesWe build all four types across the Bay Area. Detached ADUs are the most popular.
SITE ASSESSMENT, DESIGN & PERMITTING
Phase 1: Site Assessment and Design (4–8 Weeks). Everything starts with your property. Before any design work begins, we assess the lot — where utilities run, where setbacks fall, what the existing structures look like, and what the soil and drainage situation is.
From there, architectural drawings get produced. These aren’t sketches. They’re permit-ready construction documents that go to the city. Getting them right the first time matters — revisions add weeks.
Phase 2: Permitting (3–6 Months). This is the phase that surprises most homeowners. Permitting is the longest part of the process, and it’s almost entirely out of our hands once the application is submitted.
Every Bay Area city has its own timeline and its own quirks. Palo Alto, Mountain View, San Mateo, Walnut Creek — they each run their own plan check process. What we control is submitting a clean, complete set of plans that minimizes back-and-forth.
ADU Permitting Details
What Permits Cover
- Building permit (structural, architectural)
- Grading permit (if site work is needed)
- Utility connection approvals (water, sewer, electrical)
- Planning department sign-off in some jurisdictions
CONSTRUCTION
4–6 MONTHS
Once permits are approved, construction begins. For a detached ADU, this typically breaks into site preparation, foundation, framing, rough-ins, inspections, finishes, and final inspection with certificate of occupancy.
The city inspects at multiple stages: framing, rough electrical, rough plumbing, insulation, and more. The whole construction phase typically runs 4 to 6 months for a standard detached ADU. Attached ADUs and garage conversions can move faster.
WHAT CAN SLOW THINGS DOWN
Most ADU projects don’t fail — they just take longer than homeowners expect. Here’s what usually causes it:
Plan check revisions. If the city comes back with corrections, responding quickly keeps momentum. Delays on your end or ours add weeks.
Utility connections. Getting PG&E, water, and sewer to sign off on new service connections is often the longest single step outside of plan check.
Material lead times. Certain windows, doors, and fixtures have long lead times. We order early to avoid this, but it requires decisions to be made during design — not mid-construction.
Site surprises. Unexpected soil conditions, old underground utilities, or drainage issues can add cost and time. A thorough site assessment upfront catches most of these.
What We Handle So You Don’t Have To
We run a design-build operation. One team manages the entire project from initial drawings through final walkthrough.
- ✓We pull and manage all permits
- ✓We coordinate all trades (foundation, framing, electrical, plumbing, HVAC, finish)
- ✓You track everything in real time through our Buildertrend client portal
- ✓We flag issues before they become problems, not after
THE HONEST
NUMBERS
ADU costs in the Bay Area vary significantly based on size, type, site conditions, and finish level. A garage conversion typically runs less than a ground-up detached ADU. A 500 sq ft JADU costs less than an 800 sq ft standalone.
We break all of this down in a detailed estimate before any work begins. If upfront cost is a concern, we work with homeowners on financing options that make ADU construction accessible.
“Start to move-in, a typical detached ADU in the Bay Area takes 9 to 14 months. That number is real — not a sales pitch.”
— Mendez & Son’s Construction
READY TO GET STARTED?
If you’re thinking about building an ADU on your Bay Area property, the best first step is a site assessment. We’ll look at your lot, walk through what’s feasible, and give you a realistic picture of scope, cost, and timeline before you commit to anything.
The homeowners who are least frustrated by the process are the ones who understood the timeline before they started. That’s why we have this conversation first.
Weeks for Design
Site assessment through permit-ready drawings. Faster with decisive design decisions.
Months for Permits
Varies by city. We submit clean packages to minimize back-and-forth with the city.
Months for Construction
Standard detached ADU. Garage conversions and attached units can move faster.
Months Total
Start to move-in. Realistic timeline that accounts for design, permitting, and construction.
START THE
CONVERSATION
Ready to explore what an ADU could look like on your property? We’ll walk you through feasibility, timeline, and cost before you commit to anything.
Clear scope · Clear plan · Clear expectations
Serving Palo Alto · Mountain View · San Mateo
Walnut Creek · Redwood City · Bay Area