1003 Trillium Ln
Mill Valley 94941 · Tamalpais · Unincorporated Marin · Coordinates: 37.88542, -122.54553
Executive Verdict · Public-Records Synthesis
Zoned RSP-2 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 $2,214,000 ($1,948,000–$2,480,000).
Upsides & Opportunities
- ✓ ADU & SB 9 infill pathways screen as likely eligible
Zoned RSP-2 supports ministerial ADU/JADU review plus SB 9 both two-unit development and ministerial urban lot split on a 10,193 sq ft lot. Local precedent is active with 5 ADU permits within ¼ mile over the last 36 months.
Source: Unincorporated Marin zoning · CA Gov. Code 66314 & 65852.21
- ✓ Documented permitted upgrades (+$57,744 contributory est.)
Public building records show issued construction/renovation work on this parcel (7 total permits, latest Aug 25, 2023).
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)
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 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)
- ! Delayed or open permit activity on this parcel
Solar / battery storage (166083): Issued after 2 mo — slower than 90% of solar / battery storage permits in Unincorporated Marin (median 0d, 90th pct 2d, n=2,977).
Source: County of Marin Community Development Agency, Building Permits (unincorporated Marin) (review-time benchmark)
- ! 5 slow or stalled nearby projects within ½ mile
Closest lead: New home at 560 Alta Way (0.27 mi E, applied). Inspect timeline history before assuming near-term completion.
Source: County of Marin Community Development Agency, Building Permits (unincorporated Marin) · HCD APR (½-mile radius)
Parcel & Assessor
- Lot size:
- 10,193 sq ft (0.23 ac)
- Assessor use:
- Single-Resid. - Improved
- Addresses on lot:
- 1003 TRILLIUM LN
Zoning & Land Use
RSP-2 — Residential Single Family Planned (Unincorporated Marin)
State Housing Pathways Screen (ADU & SB 9)
- ADU or junior ADULikely eligible
Zoned RSP-2 (single-family residential): state law allows ADUs where homes are allowed.
- SB 9: two homes on the lotLikely eligible
Zoned RSP-2, a single-family residential zone.
- SB 9: split into two lotsLikely eligible
Zoned RSP-2, a single-family residential zone. The lot is 10,193 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 (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: $1,948,000 – $2,480,000 · 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 560 Alta Way (Applied)0.27 mi E
In "Applied" for 3.3 yr (since Aug 10, 2023), exceeding the 253d median and 686d 90th percentile for new single-family home permits in Unincorporated Marin (n=121). High-impact scale (1 housing unit, $975,000 declared valuation across 1 permit).
- Solar / battery storage (166083) (Issued)On this parcel
Issued after 2 mo — slower than 90% of solar / battery storage permits in Unincorporated Marin (median 0d, 90th pct 2d, n=2,977).
- New home at 510 Browning Ct (Issued)0.34 mi E
Active in "Issued" for 10.2 yr (first record Aug 15, 2016) with no new permit activity recorded in 9.9 yr. High-impact scale (1 housing unit, $900,000 declared valuation across 1 permit).
- New home (Entitled)0.16 mi NW
In "Entitled" for 4.8 yr (since Jan 19, 2022), 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, 52 in ½ mi · Remodel / interior alteration); Owner (4 on parcel, 31 in ½ mi · Remodel / interior alteration); Sun Metrics (1 on parcel, 1 in ½ mi · Solar / battery storage); Grc Roofing (1 on parcel, 1 in ½ mi · Roof replacement); Yonts Construction (5 in ½ mi · Remodel / interior alteration).
Permit & Project History on This Parcel (7 permits, 0 grouped projects)
| Record # | Category | Status | Applied / Issued | Valuation | Description |
|---|---|---|---|---|---|
| B35193 | Other | Issued | Iss. Aug 25, 2023 | $8,500 | 16 kWh BESS |
| B35192 | Solar / battery storage | Issued | Iss. Aug 25, 2023 | $18,000 | 3.87 kW rooftop PV system |
| B29565 | HVAC / heat pump | Issued | Iss. Apr 28, 2022 | $5,000 | Replace existing furnace and duct work. — New Ductwork, Replace Ductwork, Replace Mechanical Appliance |
| 166083 | Solar / battery storage | Issued | Iss. Oct 28, 2020 | $23,000 | 4.8kw Roof Photovoltaic & Energy Storage - Express |
| 164886 | Addition (adds square footage) | Issued | Iss. Jun 11, 2020 | $75,000 |