618 Blackstone Dr
San Rafael 94903 · Marinwood · Unincorporated Marin · Coordinates: 38.04215, -122.55120
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 $1,478,000 ($1,301,000–$1,655,000).
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
- ✓ Documented permitted upgrades (+$79,200 contributory est.)
Public building records show issued construction/renovation work on this parcel (4 total permits, latest Sep 26, 2025).
Source: County of Marin Community Development Agency, Building Permits (unincorporated Marin) (parcel APN)
- ✓ Active nearby investment (New home at 530 Blackstone Dr)
0.14 mi SE in "Issued" stage — High-impact scale ($3,000,000 declared valuation across 1 permit).
Source: County of Marin Community Development Agency, Building Permits (unincorporated Marin) · HCD APR (½-mile radius)
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
Remodel / interior alteration (180176): Issued after 8 mo (3.0× the 83d median) — above the 75th percentile for remodel / interior alteration permits in Unincorporated Marin (median 83d, 75th pct 148d, n=1,054).
Source: County of Marin Community Development Agency, Building Permits (unincorporated Marin) (review-time benchmark)
- ! Year 1 Prop 13 tax reset (~$17,447/yr at $1,478,000)
Sale triggers reassessment to 1.00% base + ~0.15% voter debt (~$1,454/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:
- 34,456 sq ft (0.79 ac)
- Assessor use:
- Single-Resid. - Improved
- Addresses on lot:
- 618 BLACKSTONE DR
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: $1,301,000 – $1,655,000 · 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
- Remodel / interior alteration (180176) (Issued)On this parcel
Issued after 8 mo (3.0× the 83d median) — above the 75th percentile for remodel / interior alteration permits in Unincorporated Marin (median 83d, 75th pct 148d, n=1,054).
- New home at 530 Blackstone Dr (Issued)0.14 mi SE
High-impact scale ($3,000,000 declared valuation across 1 permit).
Entity-resolved builders & contractors in ½ mile: Owner Builder (1 on parcel, 8 in ½ mi · Remodel / interior alteration); Dickson (1 on parcel, 1 in ½ mi · HVAC / heat pump); Northern Pacific Roofing (1 on parcel, 1 in ½ mi · Roof replacement); Mc Leran (1 on parcel, 1 in ½ mi · Roof replacement); Owner (3 in ½ mi · Remodel / interior alteration).
Permit & Project History on This Parcel (4 permits, 0 grouped projects)
| Record # | Category | Status | Applied / Issued | Valuation | Description |
|---|---|---|---|---|---|
| 180176 | Remodel / interior alteration | Issued | Iss. Sep 26, 2025 | $150,000 | Kitchen & Family Rm Interior Rmdl: Replace (E) Doors & Windows W/ Full-Height Systems, Add Bar; Remove/Replace Front Bal… |
| B42708 | Roof replacement | Issued | Iss. Jun 10, 2025 | $29,988 | Tear off existing roof down to the sheathing and replace with a Class A Composition Shingle roofing system. — ReRoofing;… |
| B35257 | HVAC / heat pump | Issued | Iss. Aug 31, 2023 | $34,000 | REPLACE 2 FURNACES, ADD 2 AC UNITS — Mechanical Appliance, Replace Mechanical Appliance |
| B22975 | Roof replacement | Issued | Iss. Jul 9, 2020 | $5,050 | Tear off 2 flat sections of the roof to solid sheeting. Re-roof with Class A Torch Down Roof system. — ReRoofing; With E… |