303 Ashton Ln
Mill Valley 94941 · Tamalpais · Unincorporated Marin · Coordinates: 37.87246, -122.53120
Executive Verdict · Public-Records Synthesis
Zoned RSP-4 in Unincorporated Marin with likely ADU & SB 9 infill eligibility and mapped CAL FIRE high fire hazard severity zone (state responsibility area) due diligence; benchmark value $2,158,000 ($1,899,000–$2,417,000).
Upsides & Opportunities
- ✓ ADU & SB 9 infill pathways screen as likely eligible
Zoned RSP-4 supports ministerial ADU/JADU review plus SB 9 both two-unit development and ministerial urban lot split on a 9,191 sq ft lot. Local precedent is active with 2 ADU permits within ¼ mile over the last 36 months.
Source: Unincorporated Marin zoning · CA Gov. Code 66314 & 65852.21
- ✓ Documented permitted upgrades (+$18,866 contributory est.)
Public building records show issued construction/renovation work on this parcel (7 total permits, latest Mar 14, 2024).
Source: County of Marin Community Development Agency, Building Permits (unincorporated Marin) (parcel APN)
- ✓ Above-average reinvestment in Tamalpais
50 substantial renovation & housing permits over 24 months (20.5 per 1,000 parcels vs. 16.4 citywide baseline) (#3 of 22 neighborhoods).
Source: County of Marin Community Development Agency, Building Permits (unincorporated Marin) (Tamalpais)
Watchouts & Due Diligence
- ! Mapped flood awareness zone (Zone X: minimal flood hazard)
about 66% 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 High 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 535 Tennessee Valley Rd (adu 531) (0.28 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 (~$25,267/yr at $2,158,000)
Sale triggers reassessment to 1.00% base + ~0.15% voter debt (~$2,106/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:
- 9,191 sq ft (0.21 ac)
- Assessor use:
- Single-Resid. - Improved
- Addresses on lot:
- 303 ASHTON LN
Zoning & Land Use
RSP-4 — Residential Single Family Planned (Unincorporated Marin)
State Housing Pathways Screen (ADU & SB 9)
- ADU or junior ADULikely eligible
Zoned RSP-4 (single-family residential): state law allows ADUs where homes are allowed.
- SB 9: two homes on the lotLikely eligible
Zoned RSP-4, a single-family residential zone.
- SB 9: split into two lotsLikely eligible
Zoned RSP-4, a single-family residential zone. The lot is 9,191 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
- High 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 (about 66% of the lot); Zone X: minimal flood hazard (about 34% of the lot) · FIRM panel 06041C0507E, 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: $1,899,000 – $2,417,000 · 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 535 Tennessee Valley Rd (adu 531) (Issued)0.28 mi E
Active in "Issued" for 6 yr (first record Oct 29, 2020) with no new permit activity recorded in 4 yr. High-impact scale (1 housing unit, $800,000 declared valuation across 1 permit).
- Accessory dwelling unit at 403 Marin Ave (adu 403a) (Issued)0.46 mi NW
Active in "Issued" for 2.9 yr (first record Dec 21, 2023) with no new permit activity recorded in 19 mo. High-impact scale (1 housing unit, $1,000,000 declared valuation across 1 permit).
- Accessory dwelling unit at 387 Countyview Dr (Applied)0.15 mi W
In "Applied" for 5.2 yr (since Sep 3, 2021), exceeding the 253d median and 686d 90th percentile for new single-family home permits in Unincorporated Marin (n=121).
- Accessory dwelling unit at 318 Via Recodo (Applied)0.21 mi S
In "Applied" for 7.4 yr (since Jun 25, 2019), exceeding the 253d median and 686d 90th percentile for new single-family home permits in Unincorporated Marin (n=121).
Entity-resolved builders & contractors in ½ mile: Owner Builder (1 on parcel, 40 in ½ mi · Remodel / interior alteration); Owner (1 on parcel, 26 in ½ mi · Remodel / interior alteration); Jaj Roofing (3 on parcel, 3 in ½ mi · Solar / battery storage); Rps Remodeling (1 on parcel, 1 in ½ mi · Windows / doors / siding); Ongaro Ernest And Sons (1 on parcel, 1 in ½ mi · HVAC / heat pump).
Permit & Project History on This Parcel (7 permits, 0 grouped projects)
| Record # | Category | Status | Applied / Issued | Valuation | Description |
|---|---|---|---|---|---|
| B37338 | Windows / doors / siding | Issued | Iss. Mar 14, 2024 | $42,500 | Install James Hardie fiber cement siding to all exterior walls of home. Approx. 4100 sq.ft. — Siding Replacement |
| B32580 | Plumbing / water heater / sewer | Issued | Iss. Feb 13, 2023 | $2,600 | Water Heater Replacement with Same — Replace Plumbing Fixtures(s); Replace Mechanical Appliance |
| 172737 | General repair | Issued | Iss. Nov 10, 2022 | $38,500 | Retaining Wall - Emergency |
| B29959 | Solar / battery storage | Issued | Iss. Jun 8, 2022 | $23,058 | PV Solar roof mount 6.40kW with 16 Panels and 16 Micro Inverters, With New 24A PV Breaker |
| B28975 | Roof replacement | Issued |