1 Unionstone Ln
San Rafael 94903 · Marinwood · Unincorporated Marin · Coordinates: 38.04077, -122.54830
Executive Verdict · Public-Records Synthesis
Zoned RMP-0.1 in Unincorporated Marin with likely ministerial ADU eligibility and mapped CAL FIRE high fire hazard severity zone (state responsibility area) due diligence; benchmark value $1,398,000 ($1,230,000–$1,566,000).
Upsides & Opportunities
- ✓ Ministerial ADU / JADU pathway likely eligible
Zone RMP-0.1 allows residential use qualifying for ministerial ADU review under state law.
Source: Unincorporated Marin zoning · CA Gov. Code 66314
- ✓ 4 documented municipal building permits on file
On-parcel permit history is indexed through May 6, 2021, 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
- ! 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)
- ! 3 slow or stalled nearby projects within ½ mile
Closest lead: 125 new homes (0.41 mi SE, entitled). 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 (~$16,527/yr at $1,398,000)
Sale triggers reassessment to 1.00% base + ~0.15% voter debt (~$1,377/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:
- 65,166 sq ft (1.50 ac)
- Assessor use:
- Single-Resid. - Improved
- Addresses on lot:
- 1 UNIONSTONE LN
Zoning & Land Use
RMP-0.1 — Residential Multiple Planned (Unincorporated Marin)
State Housing Pathways Screen (ADU & SB 9)
- ADU or junior ADULikely eligible
Zoned RMP-0.1 (multifamily residential): state law allows ADUs where homes are allowed. On a multifamily lot the state allowance is different: ADUs in non-living space of the building, plus up to eight detached ADUs.
- SB 9: two homes on the lotUnlikely
Zoned RMP-0.1 (multifamily residential), not a single-family residential zone.
- SB 9: split into two lotsUnlikely
Zoned RMP-0.1 (multifamily residential), not a single-family residential zone.
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 06041C0291D, effective May 4, 2009
- CGS Alquist-Priolo Earthquake Fault Zone
- Not in an Alquist-Priolo Earthquake Fault Zone
Surrounding Rent & Value Benchmarks (Public Records)
Range: $1,230,000 – $1,566,000 · Status: Off market
HUD Small Area FMR (ZIP 94903) · FY 2026
Studio $2,880 · 1BR $3,450 · 2BR $4,180 · 3BR $5,340 · 4BR $5,530
Developments Deserving Closer Investigation & Active Area Builders
- 125 new homes (Entitled)0.41 mi SE
In "Entitled" for 23 mo (since Dec 6, 2024), exceeding the 292d median and 313d 90th percentile for new multifamily / condos / mixed-use permits in Unincorporated Marin (n=21). High-impact scale (125 housing units, 124 deed-restricted affordable across 0 permits).
- Accessory dwelling unit at 2558 Heatherstone Dr (Applied)0.45 mi SE
In "Applied" for 5.5 yr (since Apr 29, 2021), exceeding the 253d median and 686d 90th percentile for new single-family home permits in Unincorporated Marin (n=121).
- Accessory dwelling unit at 287 Blackstone Dr (Issued)0.44 mi SE
Active in "Issued" for 19 mo (first record Apr 23, 2025) with no new permit activity recorded in 14 mo.
- New home at 530 Blackstone Dr (Issued)520 ft W
High-impact scale ($3,000,000 declared valuation across 1 permit).
Entity-resolved builders & contractors in ½ mile: Jemico (2 on parcel, 2 in ½ mi · Windows / doors / siding); Petersen Dean (1 on parcel, 1 in ½ mi · Solar / battery storage); Renewal By Andersen (1 on parcel, 1 in ½ mi · Windows / doors / siding); Owner Builder (21 in ½ mi · Remodel / interior alteration); Owner (17 in ½ mi · Remodel / interior alteration).
Permit & Project History on This Parcel (4 permits, 0 grouped projects)
| Record # | Category | Status | Applied / Issued | Valuation | Description |
|---|---|---|---|---|---|
| B25671 | Windows / doors / siding | Issued | Iss. May 6, 2021 | $19,500 | Replacing 7 retrofit windows. — Non-structural Door/Window Replacement |
| B17844 | Windows / doors / siding | Issued | Iss. May 23, 2019 | $34,584 | replacing 14 windows like for like in WUI. — Non-structural Door/Window Replacement |
| 151195 | Windows / doors / siding | Issued | Iss. Mar 15, 2016 | $12,269 | Repl Windows *Must Meet Fenestration & Wui Requirements |
| 146770 | Solar / battery storage | Issued | Iss. Apr 22, 2015 | $31,874 | Rf Mtd P V Sys 8.25 K W - Express |