ADU Design Services
Build More Possibility Into Your Property
An Accessory Dwelling Unit can create space for family, generate rental income, support aging parents, or give you a private home office just steps from your house.
Since 2000, Andrea Costanzo has helped Bay Area homeowners design and complete more than 100 ADU projects, guiding clients through design, city approvals, permitting, and construction.
Serving San Mateo, Burlingame, Millbrae, South San Francisco, Belmont, San Carlos, Hillsborough, Foster City, Redwood City, and nearby Peninsula communities.
Why Now Is a Great Time to Build an ADU
- Create a private home for parents, adult children, or guests
- Generate long-term rental income
- Add a dedicated office, studio, or flexible living space
- Increase the usefulness and value of your property
- Make better use of an existing garage, backyard, or underused area
Types & scope
Detached ADUs
A standalone unit built separately from the main home. Great for rental income, family members, guests, or a private workspace.
Attached ADUs
An ADU connected to the existing home, often designed as an addition or reconfiguration of the existing structure.
Garage Conversions
A practical way to transform an underused garage into livable space.
Junior ADUs
A smaller unit created within the existing home, often using an existing bedroom or interior area.
Feasibility & Site Planning
Feasibility and early design direction, site planning, and layout options — before you commit to a scope.
City Submittals & Permitting
Architectural plans, city submittals, permit coordination, responses to city comments, and construction support.
Why work with Andrea
Local Experience That Helps Projects Move Forward
Designing an ADU is about more than fitting a unit into your backyard or converting a garage. Every city has its own process, requirements, submittals, and review expectations.
Since 2000, Andrea Costanzo has worked with homeowners throughout the San Francisco Peninsula. Her experience is not only in design, but in understanding how local cities review projects, what they look for, and how to prepare plans that are more likely to move through approval efficiently.
- Serving Bay Area homeowners since 2000
- 100+ ADUs designed and completed
- Deep knowledge of local planning and permitting processes
- Experience with remodels, additions, and new homes
- Personal guidance from concept through construction
Featured Projects
View All ProjectsPlaceholder photography — to be replaced with Andrea's project photos.
Our process
Our ADU Process
- 01
Consultation
We start by understanding your goals, property, timeline, and budget.
- 02
Feasibility & Design Direction
Andrea reviews your property and helps identify what type of ADU may make the most sense.
- 03
Architectural Design
We create plans that balance your needs, your property, and local requirements.
- 04
City Submittal & Permits
Andrea prepares the plans and helps guide the project through city review and approval.
- 05
Construction Support
Andrea stays involved during construction to help answer questions and keep the project aligned with the approved design.
FAQs
Frequently Asked Questions
Is my property eligible for an ADU?
Many Bay Area properties may qualify for an ADU, but the best option depends on your lot, existing home, utilities, access, setbacks, and city requirements. Andrea can help you evaluate what is possible.
How long does an ADU take?
Timelines vary depending on the city, scope, design complexity, and construction team. The right plans and a clear permitting strategy can help reduce unnecessary delays.
Can I build an ADU in my backyard?
Often, yes. A detached backyard ADU is one of the most common options, but feasibility depends on your property layout and local requirements.
Can I convert my garage into an ADU?
In many cases, yes. Garage conversions can be a cost-effective way to add livable space, especially when the existing structure is suitable.
Can Andrea help with permits?
Yes. Andrea prepares architectural plans and helps guide homeowners through city submittals, review comments, and approval.
What cities do you work in?
Andrea serves homeowners across the Peninsula, including San Mateo, Burlingame, Millbrae, South San Francisco, Belmont, San Carlos, Hillsborough, Foster City, Redwood City, and nearby communities.
Ready to start?
Ready to Explore an ADU?
Whether you are just starting to research or already know what you want to build, Andrea can help you understand what is possible and guide your project from idea to approval and construction.