Planning an ADU can feel like a lot at first. There are decisions to make, timelines to understand, and costs to consider. The good news is you don’t have to sort through it alone.
At the San Mateo County ADU Resource Center, we work with homeowners every day to help make the process clearer and more manageable. In a recent webinar with Hello Housing, we walked through the full ADU path from early planning to move in. What stood out was how much easier it is to move forward when you have a clear understanding of your options and a place to go with questions.
Here’s how to get started, and where we can support you along the way.
1. Start by exploring your ADU options
Every project begins with a vision. Some homeowners choose a junior ADU, by converting an existing space like a garage or basement, which is smaller and often more cost friendly. Others may choose an attached unit or a detached backyard home. Each option opens up different possibilities depending on your goals, your property, and your budget.
2. Get to know your property
Every site has its own story. Things like soil conditions, the typography of your lot, easements and access can shape what’s possible. This is where early insight really helps. Our free feasibility consultations give you a chance to ask questions, learn from an ADU specialist, and better understand the factors that may shape your project.
3: Choose a construction approach
Once you have a sense of how you want to use your ADU, along with the number of rooms and features you’d like, the next step is deciding how to build. Some projects are constructed on site, while others use panelized or modular systems, which are built in a factory off-site and delivered or assembled on your property. Prefab options can save time, but it’s important to understand the full picture, as costs like foundation work, delivery, and taxes can add up. We can help you look at each option clearly so you can make a choice that is grounded in the latest information.
4. Understand the rules and how they apply to you
State laws have made it easier to build ADUs, but local guidelines still shape each project. Connecting with your city or town early can help everything move more smoothly. If you’re not sure where to start, we’ll help point you in the right direction and make those connections easier. You may be interested in our March 2026 post about housing policy.
5. Create a plan and a timeline
With a direction in place, you can start mapping out your project. Most ADUs move through planning, design, permitting, and construction. Timelines vary, but having a plan helps everything stay on track. We have resources that can help you along the way.
6. Plan your budget
A strong plan includes a clear budget. Beyond construction, there are design, permitting, and utility considerations to keep in mind. Looking at the full cost early on helps you avoid surprises and make informed decisions along the way. Check out the budgeting section of our website.
These are the big steps. And while they’re important, you don’t have to tackle them alone. We’re here to help you keep things moving.
A few practical tips can also make a difference along the way.
PLAN AHEAD FOR UTILITIES
Utility timelines can vary depending on demand and scheduling. Getting this on your list early helps avoid delays later and keeps your project moving forward.
TAKE TIME TO FIND THE RIGHT CONTRACTOR
Meeting with a few contractors and comparing proposals can give you a clearer picture of your options. Look for detailed, thoughtful bids and experience with ADUs. This is a great place to learn and ask questions, and we have additional resources to help guide you through that process.