The Mill Valley Pool House
ADU and Garage Conversion Specialists in Mill Valley
WDC builds accessory dwelling units in Mill Valley — garage conversions, detached guest houses, and junior ADUs — managing design, permitting, and construction as a single coordinated scope. Mill Valley has some of the best ADU opportunity in the San Fernando Valley: large lots, attached garages, and a multigenerational population that benefits from flexible living arrangements on a single property.
ADU Rules in Mill Valley
Mill Valley is in Marin County — the City of Mill Valley Building Division jurisdiction. California state ADU law applies, and the City of SF has implemented the state framework with its own supplemental requirements:
- Detached ADUs — up to 1,200 sqft on most single-family lots; setbacks and lot coverage limits apply based on zone
- Garage conversions (ADU) — attached and detached garages are convertible to living space; replacement parking generally not required under current California law
- Junior ADUs (JADUs) — up to 500 sqft within the primary residence with separate entry; owner-occupancy requirement applies
- Fire zone requirements — ADUs on properties within SF’s Very High Fire Hazard Severity Zone require ignition-resistant construction for exterior elements; some Mill Valley hillside properties fall within this designation
- SB 543 (2026) — ADUs at or under 750 sqft are exempt from school developer fees under current California law
- the City of Mill Valley Building Division ADU plan check — standard ADU applications in Mill Valley are processed through the City of Mill Valley Building Division Mill Valley; straightforward garage conversions typically run 4–8 weeks in plan check
ADU Types We Build in Mill Valley
- Detached ADU / Guest House — new construction on existing lot; ideal for Mill Valley properties with large rear yards
- Garage Conversion — single or double attached garage converted to full living space; the most common ADU type in Mill Valley given the Valley’s car-centric ranch home stock
- JADU (Junior ADU) — interior conversion within the primary home; separate entry, kitchenette, private bath
- Above-Garage ADU — second story addition above existing garage; requires structural engineering and the City of Mill Valley Building Division review
Every WDC ADU includes full scope: electrical, plumbing, HVAC, insulation, windows, finishes, and complete permit management. No surprise line items.
Why ADUs Work in Mill Valley
Mill Valley sits in one of the most ADU-favorable conditions in San Francisco. Large single-family lots — common in the Valley grid — offer room for detached units. The area’s multigenerational family culture makes on-property guest quarters and family suites a practical investment. Rental demand in the 91401, 91403, and 91423 zip codes is strong, and ADU rental income increasingly offsets renovation costs for homeowners who plan ahead.
If an ADU is part of a broader renovation — kitchen, baths, and primary suite alongside the garage conversion — WDC can coordinate all of it under a single permit pull. One plan check, one construction schedule, one disruption period.
Our ADU Process in Mill Valley
Step 1 — Site Assessment and Feasibility
We assess your lot, existing structure, and zone to confirm ADU type, size, setbacks, and fire zone status. Garage conversions in Mill Valley are often feasible with minimal site preparation — we confirm exactly what your property allows before any design work begins.
Step 2 — Design and Engineering
Our design partners produce permit-ready drawings. For garage conversions, structural review is included to confirm the existing slab, framing, and roof structure meet living space requirements.
Step 3 — Permit Submission
We submit to the City of Mill Valley Building Division Mill Valley and manage plan check through approval. Standard garage conversion plan check typically runs 4–8 weeks; detached ADUs may take longer depending on lot complexity.
Step 4 — Construction
Our crews build to a single scope under one site supervisor. Finish selections are confirmed before construction starts. Clients receive weekly photo updates throughout the build.
Step 5 — Final Inspection and Delivery
Certificate of occupancy, utility connections, and a full documentation package. Ready for occupancy, family use, or rental from day one.
Mill Valley ADU — Frequently Asked Questions
Can I convert my attached garage to an ADU in Mill Valley?
Yes. Attached garage conversions are one of the most common ADU projects in Mill Valley. The existing slab, foundation, and roof structure are often usable as-is, which reduces construction cost and complexity relative to new detached construction. WDC confirms structural adequacy during the feasibility assessment.
How long does an ADU take in Mill Valley?
Garage conversions typically take 6–10 months from contract to certificate of occupancy — including design, plan check, and construction. Detached ADUs requiring new foundation work run longer, typically 9–13 months.
Do I lose my parking if I convert the garage?
Under current California ADU law, replacement parking is generally not required when converting an existing garage to an ADU. This applies in Mill Valley. We confirm the specific requirements for your property and zone during feasibility.
Can the ADU be rented out?
Yes. ADUs in Mill Valley can be rented as long-term rental units. Short-term rental (under 30 days) is subject to the City of SF’s home-sharing ordinance and registration requirements. Confirm rental intent with the City or your attorney if short-term use is the goal.
Build Your Mill Valley ADU
Mill Valley garage conversions are some of the most straightforward ADU projects in the Valley — and some of the most impactful for families who want flexibility on their property. A consultation with WDC confirms feasibility and maps the permit path before you commit to design.
Request a consultation(415) 416-5494