70 A Shell Rd
Mill Valley 94941 · Alto · Unincorporated Marin · Coordinates: 37.90647, -122.52342
Executive Verdict · Public-Records Synthesis
Zoned RA-B2 in Unincorporated Marin with likely ministerial ADU eligibility and mapped FEMA AO flood due diligence; benchmark value $2,204,000 ($1,940,000–$2,468,000).
Upsides & Opportunities
- ✓ Ministerial ADU / JADU pathway likely eligible
Zone RA-B2 allows residential use qualifying for ministerial ADU review under state law (3 ADU permits permitted within ¼ mile in 36 months).
Source: Unincorporated Marin zoning · CA Gov. Code 66314
- ✓ 4 documented municipal building permits on file
On-parcel permit history is indexed through Mar 11, 2024, letting you verify roof, HVAC, electrical, or structural work against seller disclosures.
Source: County of Marin Community Development Agency, Building Permits (unincorporated Marin) (parcel APN)
Watchouts & Due Diligence
- ! FEMA Special Flood Hazard Area (AO, all of the lot of lot)
Zone AO: 1% annual chance flood (Special Flood Hazard Area) overlaps this parcel. Expect mandatory flood insurance for federally backed loans and floodplain elevation/mitigation rules for new units or SB 9 applications.
Source: FEMA National Flood Hazard Layer (parcel polygon)
- ! Delayed or open permit activity on this parcel
Accessory dwelling unit at 70 Shell Rd: In "Applied" for 4.2 yr (since Aug 18, 2022), exceeding the 253d median and 686d 90th percentile for new single-family home permits in Unincorporated Marin (n=121).
Source: County of Marin Community Development Agency, Building Permits (unincorporated Marin) (review-time benchmark)
- ! 4 slow or stalled nearby projects within ½ mile
Closest lead: New home at 30 Shell Rd (0.26 mi E, issued). Inspect timeline history before assuming near-term completion.
Source: County of Marin Community Development Agency, Building Permits (unincorporated Marin) · HCD APR (½-mile radius)
- ! Year 1 Prop 13 tax reset (~$25,796/yr at $2,204,000)
Sale triggers reassessment to 1.00% base + ~0.15% voter debt (~$2,150/mo). Confirm exact Mello-Roos / CFD special assessments on the county tax bill.
Source: CA Const. Art. XIIIA (Prop 13) · County Tax Collector
Parcel & Assessor
- Lot size:
- 13,329 sq ft (0.31 ac)
- Assessor use:
- Single-Resid. - Improved
- Addresses on lot:
- 70A SHELL RD; 70 SHELL RD
Zoning & Land Use
RA-B2 — Residential Agriculture (Unincorporated Marin)
State Housing Pathways Screen (ADU & SB 9)
- ADU or junior ADULikely eligible
Zoned RA-B2 (single-family residential): state law allows ADUs where homes are allowed.
- SB 9: two homes on the lotCan't tell
Zoned RA-B2 (single-family residential): we can't tell whether it counts as a single-family zone for SB 9. Residential agriculture, estate and restricted: large-lot residential; confirm SB 9 with the county.
- SB 9: split into two lotsCan't tell
Zoned RA-B2 (single-family residential): we can't tell whether it counts as a single-family zone for SB 9. Residential agriculture, estate and restricted: large-lot residential; confirm SB 9 with the county.
Mapped Hazard Zones on This Lot
- CAL FIRE Fire Hazard Severity Zone
- Not in a State-mapped fire hazard severity zone
- FEMA National Flood Hazard Layer
- Zone AO: 1% annual chance flood (Special Flood Hazard Area) (all of the lot) · FIRM panel 06041C0467F, effective March 16, 2016
- CGS Alquist-Priolo Earthquake Fault Zone
- Not in an Alquist-Priolo Earthquake Fault Zone
Surrounding Rent & Value Benchmarks (Public Records)
Range: $1,940,000 – $2,468,000 · Status: Off market
HUD Small Area FMR (ZIP 94941) · FY 2026
Studio $2,730 · 1BR $3,270 · 2BR $3,960 · 3BR $5,060 · 4BR $5,240
Developments Deserving Closer Investigation & Active Area Builders
- Accessory dwelling unit at 70 Shell Rd (Applied)On this parcel
In "Applied" for 4.2 yr (since Aug 18, 2022), exceeding the 253d median and 686d 90th percentile for new single-family home permits in Unincorporated Marin (n=121).
- Accessory dwelling unit (new or conversion) (90233) (Applied)On this parcel
Pending in review for 4.2 yr (7.6× the 204d median) — slower than 90% of accessory dwelling unit (new or conversion) permits in Unincorporated Marin (median 204d, 90th pct 549d, n=298).
- New home at 30 Shell Rd (Issued)0.26 mi E
Active in "Issued" for 2.4 yr (first record Jul 5, 2024) with no new permit activity recorded in 22 mo. High-impact scale (1 housing unit, $2,800,000 declared valuation across 1 permit).
- Accessory dwelling unit at 55 Plaza Dr (adu 55a) (Issued)0.33 mi SE
Active in "Issued" for 2.6 yr (first record Apr 17, 2024) with no new permit activity recorded in 19 mo. High-impact scale (1 housing unit, $790,000 declared valuation across 1 permit).
Entity-resolved builders & contractors in ½ mile: Window And Door Factory Of California (1 on parcel, 1 in ½ mi · Windows / doors / siding); Cost U Less Roofing (1 on parcel, 1 in ½ mi · Roof replacement); Divine Electric (1 on parcel, 1 in ½ mi · EV charger); Owner Builder (18 in ½ mi · Addition (adds square footage)); Owner (9 in ½ mi · Addition (adds square footage)).
Permit & Project History on This Parcel (4 permits, 1 grouped projects)
| Record # | Category | Status | Applied / Issued | Valuation | Description |
|---|---|---|---|---|---|
| B37285 | Windows / doors / siding | Issued | Iss. Mar 11, 2024 | $22,000 | Replace 15 windows and 1 patio sliding glass door like for like — Non-structural Door/Window Replacement |
| B37186 | EV charger | Issued | Iss. Mar 4, 2024 | $4,200 | Replace 100 AMP Main Service Panel with new 200 AMP Main service Panel in same location. Install 40 AMP Electric Vehicle… |
| 90233 | Accessory dwelling unit (new or conversion) | Applied | App. Aug 18, 2022 | $300,000 | Detached A D U |
| B23384 | Roof replacement | Issued | Iss. Aug 27, 2020 | $13,750 |