492 Blackstone Dr
San Rafael 94903 · Marinwood · Unincorporated Marin · Coordinates: 38.03933, -122.54854
Executive Verdict · Public-Records Synthesis
Zoned R1-B2 in Unincorporated Marin with likely ADU & SB 9 infill eligibility and mapped CAL FIRE high fire hazard severity zone (local responsibility area) due diligence; benchmark value $1,348,000 ($1,186,000–$1,510,000).
Upsides & Opportunities
- ✓ ADU & SB 9 infill pathways screen as likely eligible
Zoned R1-B2 supports ministerial ADU/JADU review plus SB 9 both two-unit development and ministerial urban lot split on a 12,937 sq ft lot.
Source: Unincorporated Marin zoning · CA Gov. Code 66314 & 65852.21
- ✓ Documented permitted upgrades (+$15,868 contributory est.)
Public building records show issued construction/renovation work on this parcel (5 total permits, latest Jul 17, 2024).
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 (Local 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 Mar 24, 2025)
- ! Delayed or open permit activity on this parcel
Plumbing / water heater / sewer (159738): Issued after 2 mo — slower than 90% of plumbing / water heater / sewer permits in Unincorporated Marin (median 0d, 90th pct 0d, n=2,211).
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: 125 new homes (0.39 mi E, 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)
Parcel & Assessor
- Lot size:
- 12,937 sq ft (0.30 ac)
- Assessor use:
- Single-Resid. - Improved
- Addresses on lot:
- 492 BLACKSTONE DR
Zoning & Land Use
R1-B2 — Residential Single Family (Unincorporated Marin)
State Housing Pathways Screen (ADU & SB 9)
- ADU or junior ADULikely eligible
Zoned R1-B2 (single-family residential): state law allows ADUs where homes are allowed.
- SB 9: two homes on the lotLikely eligible
Zoned R1-B2, a single-family residential zone.
- SB 9: split into two lotsLikely eligible
Zoned R1-B2, a single-family residential zone. The lot is 12,937 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 (Local Responsibility Area) (all of the lot, map Mar 24, 2025)
- 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: $1,186,000 – $1,510,000 · 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)0.39 mi E
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).
- Plumbing / water heater / sewer (159738) (Issued)On this parcel
Issued after 2 mo — slower than 90% of plumbing / water heater / sewer permits in Unincorporated Marin (median 0d, 90th pct 0d, n=2,211).
- Accessory dwelling unit at 2558 Heatherstone Dr (Applied)0.4 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)0.42 mi E
Active in "Issued" for 19 mo (first record Apr 23, 2025) with no new permit activity recorded in 14 mo.
Entity-resolved builders & contractors in ½ mile: Solar Technologies (2 on parcel, 2 in ½ mi · Electrical / panel); Earl Adams Tile Coping And Plastering Adams Pool Solutions (1 on parcel, 1 in ½ mi · Plumbing / water heater / sewer); Ste Electric (1 on parcel, 1 in ½ mi · Solar / battery storage); Giovacchini Construction (1 on parcel, 1 in ½ mi · General repair); Owner Builder (30 in ½ mi · Remodel / interior alteration).
Permit & Project History on This Parcel (5 permits, 0 grouped projects)
| Record # | Category | Status | Applied / Issued | Valuation | Description |
|---|---|---|---|---|---|
| 177105 | General repair | Issued | Iss. Jul 17, 2024 | $4,779 | Seismic Retrofit In Accordance With Plan Set A |
| B30082 | Solar / battery storage | Issued | Iss. Jun 17, 2022 | $15,200 | 1 AC Battery Installation |
| 159738 | Plumbing / water heater / sewer | Issued | Iss. Oct 1, 2018 | $43,940 | Pool Repair, Replace Electrical & Plumbing T.D. 8/17/18 |
| 158197 | Solar / battery storage | Issued | Iss. Apr 12, 2018 | $29,894 | P V Sys 5.03 K W - Not Express |
| 158196 | Electrical / panel | Issued | Iss. Apr 12, 2018 | $500 |