323 Seymour Ln
Mill Valley 94941 · Homestead · Unincorporated Marin · Coordinates: 37.89866, -122.54383
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 $2,584,000 ($2,274,000–$2,894,000).
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 22,956 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 (+$228,480 contributory est.)
Public building records show issued construction/renovation work on this parcel (11 total permits, latest Jul 31, 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)
- ! Delayed or open permit activity on this parcel
New garage / accessory structure (182282): Issued after 17 mo (3.2× the 164d median) — slower than 90% of new garage / accessory structure permits in Unincorporated Marin (median 164d, 90th pct 485d, n=356).
Source: County of Marin Community Development Agency, Building Permits (unincorporated Marin) (review-time benchmark)
- ! Year 1 Prop 13 tax reset (~$30,166/yr at $2,584,000)
Sale triggers reassessment to 1.00% base + ~0.15% voter debt (~$2,514/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:
- 22,956 sq ft (0.53 ac)
- Assessor use:
- Single-Resid. - Improved
- Addresses on lot:
- 323 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 22,956 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: $2,274,000 – $2,894,000 · 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 garage / accessory structure (182282) (Issued)On this parcel
Issued after 17 mo (3.2× the 164d median) — slower than 90% of new garage / accessory structure permits in Unincorporated Marin (median 164d, 90th pct 485d, n=356).
- Other (182281) (Issued)On this parcel
Issued after 17 mo — slower than 90% of other permits in Unincorporated Marin (median 0d, 90th pct 71d, n=1,560).
- General repair (182280) (Issued)On this parcel
Issued after 17 mo (6.3× the 83d median) — slower than 90% of general repair permits in Unincorporated Marin (median 83d, 90th pct 328d, n=693).
- Other (92986) (Applied)On this parcel
Pending in review for 21 mo — slower than 90% of other permits in Unincorporated Marin (median 0d, 90th pct 71d, n=1,560).
Entity-resolved builders & contractors in ½ mile: Owner Builder (5 on parcel, 49 in ½ mi · Remodel / interior alteration); Luminalt Energy (1 on parcel, 1 in ½ mi · Solar / battery storage); Quevedo Roofing (1 on parcel, 1 in ½ mi · Roof replacement); William Gotelli Plumbing (1 on parcel, 1 in ½ mi · Plumbing / water heater / sewer); Owner (20 in ½ mi · Remodel / interior alteration).
Permit & Project History on This Parcel (11 permits, 0 grouped projects)
| Record # | Category | Status | Applied / Issued | Valuation | Description |
|---|---|---|---|---|---|
| 182283 | General repair | Issued | Iss. Jul 31, 2026 | $10,000 | Wood Wall Near Parking Area |
| 182282 | New garage / accessory structure | Issued | Iss. Jul 31, 2026 | — | Gable Roof Covered Gate Entrryways |
| 182281 | Other | Issued | Iss. Jul 31, 2026 | $5,000 | Railings At Concrete Stairs |
| 182280 | General repair | Issued | Iss. Jul 31, 2026 | $150,000 | Concrete Retaining Walls With Stone Facing; Stone Retaining Walls; Stone & Wood Wall |
| B45208 | Solar / battery storage | Issued | Iss. Dec 17, 2025 | $48,235 |