317 Seymour Ln
Mill Valley 94941 · Homestead · Unincorporated Marin · Coordinates: 37.89886, -122.54364
Executive Verdict · Public-Records Synthesis
Zoned R1-B1 in Unincorporated Marin with likely ADU & SB 9 infill eligibility and mapped CAL FIRE moderate fire hazard severity zone (state responsibility area) due diligence; benchmark value $2,059,000 ($1,812,000–$2,306,000).
Upsides & Opportunities
- ✓ ADU & SB 9 infill pathways screen as likely eligible
Zoned R1-B1 supports ministerial ADU/JADU review plus SB 9 both two-unit development and ministerial urban lot split on a 3,877 sq ft lot. Local precedent is active with 1 ADU permit within ¼ mile over the last 36 months.
Source: Unincorporated Marin zoning · CA Gov. Code 66314 & 65852.21
- ✓ Documented permitted upgrades (+$6,400 contributory est.)
Public building records show issued construction/renovation work on this parcel (4 total permits, latest Feb 27, 2026).
Source: County of Marin Community Development Agency, Building Permits (unincorporated Marin) (parcel APN)
- ✓ Above-average reinvestment in Homestead
22 substantial renovation & housing permits over 24 months (20.7 per 1,000 parcels vs. 16.4 citywide baseline) (#2 of 22 neighborhoods).
Source: County of Marin Community Development Agency, Building Permits (unincorporated Marin) (Homestead)
Watchouts & Due Diligence
- ! Mapped flood awareness zone (Zone X: minimal flood hazard)
all of the lot of the parcel intersects Zone X: minimal flood hazard. Outside mandatory federal SFHA insurance rules, but check local drainage and finished-floor requirements.
Source: FEMA National Flood Hazard Layer (parcel polygon)
- ! CAL FIRE Moderate Fire Hazard Severity Zone (State Responsibility Area) (all of the lot of lot)
Located in a mapped Fire Hazard Severity Zone. Expect Chapter 7A ignition-resistant building standards, defensible-space inspections, and stricter property insurance underwriting.
Source: CAL FIRE FHSZ (map Apr 1, 2024)
- ! 6 slow or stalled nearby projects within ½ mile
Closest lead: New home at 107 Montford Ave (0.2 mi SE, 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 (~$24,129/yr at $2,059,000)
Sale triggers reassessment to 1.00% base + ~0.15% voter debt (~$2,011/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:
- 3,877 sq ft (0.09 ac)
- Assessor use:
- Single-Resid. - Improved
- Addresses on lot:
- 317 SEYMOUR LN
Zoning & Land Use
R1-B1 — Residential Single Family (Unincorporated Marin)
State Housing Pathways Screen (ADU & SB 9)
- ADU or junior ADULikely eligible
Zoned R1-B1 (single-family residential): state law allows ADUs where homes are allowed.
- SB 9: two homes on the lotLikely eligible
Zoned R1-B1, a single-family residential zone.
- SB 9: split into two lotsLikely eligible
Zoned R1-B1, a single-family residential zone. The lot is 3,877 sq ft by the assessor, room for two lots of at least 1,200 sq ft, each at least 40% of the original.
Mapped Hazard Zones on This Lot
- CAL FIRE Fire Hazard Severity Zone
- Moderate Fire Hazard Severity Zone (State Responsibility Area) (all of the lot, map Apr 1, 2024)
- FEMA National Flood Hazard Layer
- Zone X: minimal flood hazard (all of the lot) · FIRM panel 06041C0468F, 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: $1,812,000 – $2,306,000 · 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
- New home at 107 Montford Ave (Issued)0.2 mi SE
Active in "Issued" for 3.9 yr (first record Dec 15, 2022) with no new permit activity recorded in 2.5 yr. High-impact scale (1 housing unit, $1,375,000 declared valuation across 1 permit).
- Accessory dwelling unit at 408 Laverne Ave (adu 408a) (Issued)0.31 mi W
Active in "Issued" for 2.3 yr (first record Jul 12, 2024) with no new permit activity recorded in 14 mo. High-impact scale (1 housing unit, $2,700,000 declared valuation across 1 permit).
- New home at 420 Laverne Ave (Issued)0.35 mi W
Active in "Issued" for 8.6 yr (first record Apr 23, 2018) with no new permit activity recorded in 3.8 yr. High-impact scale (1 housing unit, $1,100,000 declared valuation across 1 permit).
- New home at 204 Reed St (Issued)0.4 mi S
Active in "Issued" for 4.3 yr (first record Aug 5, 2022) with no new permit activity recorded in 3.5 yr. High-impact scale (1 housing unit, $950,000 declared valuation across 1 permit).
Entity-resolved builders & contractors in ½ mile: Tesla Energy (1 on parcel, 1 in ½ mi · Solar / battery storage); Earth Star Electric (1 on parcel, 1 in ½ mi · Electrical / panel); Divine Electric (1 on parcel, 1 in ½ mi · Electrical / panel); Home Depot USA (1 on parcel, 1 in ½ mi · Windows / doors / siding); Owner Builder (46 in ½ mi · Remodel / interior alteration).
Permit & Project History on This Parcel (4 permits, 0 grouped projects)
| Record # | Category | Status | Applied / Issued | Valuation | Description |
|---|---|---|---|---|---|
| B46032 | Electrical / panel | Issued | Iss. Feb 27, 2026 | $3,500 | Service Upgrade |
| B26483 | Electrical / panel | Issued | Iss. Aug 3, 2021 | $4,500 | Electrical service upgrade 200A — Service Upgrade |
| B26438 | Windows / doors / siding | Issued | Iss. Jul 29, 2021 | $3,217 | Replace 3 windows with retrofit vinyl windows. — Non-structural Door/Window Replacement |
| 168661 | Solar / battery storage | Issued | Iss. Jun 30, 2021 | $13,040 | 4.08kw Rooftop Photovoltaic & Energy Storage System |