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Custom ADU Design & Construction in Mill Valley
Upgrade your property with a thoughtfully designed ADU. Sidex manages planning, construction, and project coordination to deliver beautiful, functional living spaces built for Mill Valley homeowners.
4.9/5 rating from 56+ online reviews.

Building a Mill Valley ADU That Fits the Way You Live
Mill Valley homeowners value good design. Whether it’s preserving the character of a hillside property, improving functionality, or making better use of available land, every improvement should feel intentional.
That’s why ADUs have become one of the most practical investments for Bay Area properties. A well-designed ADU can enhance the usability of your home while blending naturally with the surrounding architecture and landscape. As experienced ADU builders in Mill Valley, Sidex provides complete project support. Our team understands the unique challenges that come with ADU construction in Mill Valley, including lot constraints, elevation changes, and local permitting requirements.
Custom ADU Services in Mill Valley

Detached ADUs

Attached ADUs

Granny Flats

Backyard Cottages

In-Law Suites

Garage Conversions

Prefab ADUs
Custom ADU Services in Mill Valley

Detached ADUs

Attached ADUs

Granny Flats

Backyard Cottages

In-Law Suites

Garage Conversions

Prefab ADUs
Custom ADU Services in Mill Valley

In-Law
Suites

Garage Conversions

Prefab ADUs
Structural Excellence & Outdoor Integration in Mill Valley
Exceptional ADU projects start with strong construction expertise. Our gallery features outdoor living and structural projects, reflecting attention to detail, craftsmanship, and project execution that defines every ADU we build in Mill Valley and the Bay Area.
EXCELLENT
Based on 38 reviews
Posted on Google![]()
Tatyana PTrustindex verifies that the original source of the review is Google.
Posted on Google![]()
Vivi BabenkoTrustindex verifies that the original source of the review is Google.
My grandparents backyard deck had taken a beating over the years, especially from all the snow and rough weather. It was definitely time for some love, and Sidex really came through for! What stood out most was the crew and how they treated my grandparents like family and were genuinely so kind throughout the whole project. Really glad we chose them!Posted on Google![]()
Sara YarmolyukTrustindex verifies that the original source of the review is Google.
Extremely helpful employees and truly have honest work and craftsmanship.Posted on Google![]()
Valya StepanovTrustindex verifies that the original source of the review is Google.
I can’t say enough good things about Sidex Siding & Decking! From the first phone call to the final walkthrough, the entire experience was outstanding. The team was professional, punctual, and incredibly knowledgeable. They took the time to answer all of my questions, communicated clearly throughout the project, and paid close attention to every detail. The quality of their workmanship exceeded my expectations, and the finished deck looks absolutely amazing. They treated my home with respect, kept the work area clean, and completed everything on schedule. It’s rare to find a company that truly delivers on its promises, but Sidex Siding & Decking did exactly that. If you’re looking for a trustworthy, skilled, and reliable contractor, I highly recommend them. I couldn’t be happier with the results and will definitely use them again for future projects. Five stars all the way!Posted on Google![]()
Max GatsmanyukTrustindex verifies that the original source of the review is Google.
Fast and professionalPosted on Google![]()
Vince CartersonTrustindex verifies that the original source of the review is Google.
Andrey and Nate were very helpful, would work with Sidex again. I am glad everything went as smooth as they said it would.Posted on Google![]()
Sava VashchukTrustindex verifies that the original source of the review is Google.
We recently hired SIDEX to completely replace the old, worn-out siding on our home and we could not be happier with the results. They gave us a highly competitive and transparent quote with no hidden fees.Posted on Google![]()
Rita SnizhkoTrustindex verifies that the original source of the review is Google.
We couldn’t be happier with how our new deck turned out! From the very beginning, the whole process was so easy, and the Sidex Construction team was amazing to work with. They really listened to what we wanted and brought our vision to life exactly how we imagined it! Our outdoor space has completely transformed, and it’s now one of our favorite places to relax. It’s exactly what we had in mind for our home, and we honestly couldn’t have asked for a better result. We highly recommend Sidex Construction to anyone looking for quality work!Posted on Google![]()
Amanda KilgoreTrustindex verifies that the original source of the review is Google.
Had a great experience working with Sidex. Nate was super helpful during the in-person site visit and took the time to explain everything clearly without making us feel rushed or pressured. Andrey was also very helpful with scheduling and keeping everything organized throughout the process. The whole team was professional, easy to work with, and communication was solid from start to finish. Really appreciated how smooth everything went. Would definitely recommend Sidex to anyone looking for quality work and good customer service.Posted on Google![]()
Marjorie SiemsenTrustindex verifies that the original source of the review is Google.
Tim did a wonderful job fixing a leak on my skylight windows. Totally professional and very detailed in his work. I would definitely consider him for future work!
FAQs About ADUs in Mill Valley
What is an ADU?
An ADU, or accessory dwelling unit, is a secondary residential structure located on the same property as a primary home.
Why are ADUs popular in Mill Valley?
Many homeowners choose ADUs to create additional usable space while preserving the character and location of their existing property.
Do you handle permits and planning?
Yes. Our team assists with project planning, permitting coordination, and key steps throughout the construction process.
What types of ADUs do you build?
We build detached ADUs, attached ADUs, granny flats, backyard cottages, garage conversions, and prefab ADUs.
Can an ADU increase property value?
A professionally designed and constructed ADU can improve property flexibility and long-term market appeal.
Why choose Sidex for ADU construction?
As trusted ADU contractors in Mill Valley, we combine thoughtful design, quality craftsmanship, and a streamlined building process.




