230 Blackstone Dr
San Rafael 94903 · Marinwood · Unincorporated Marin · Coordinates: 38.03749, -122.53880
Executive Verdict · Public-Records Synthesis
Zoned R1 in Unincorporated Marin with likely ADU & SB 9 infill eligibility and mapped CAL FIRE moderate fire hazard severity zone (local responsibility area) due diligence; benchmark value $1,304,000 ($1,148,000–$1,460,000).
Upsides & Opportunities
- ✓ ADU & SB 9 infill pathways screen as likely eligible
Zoned R1 supports ministerial ADU/JADU review plus SB 9 both two-unit development and ministerial urban lot split on a 9,017 sq ft lot. Local precedent is active with 3 ADU permits within ¼ mile over the last 36 months.
Source: Unincorporated Marin zoning · CA Gov. Code 66314 & 65852.21
- ✓ Documented permitted upgrades (+$7,524 contributory est.)
Public building records show issued construction/renovation work on this parcel (4 total permits, latest Jan 5, 2026).
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 Moderate Fire Hazard Severity Zone (Local Responsibility Area) (about 17% 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
New garage / accessory structure (180842): Issued after 13 mo (2.5× the 164d median) — above the 75th percentile for new garage / accessory structure permits in Unincorporated Marin (median 164d, 75th pct 294d, n=356).
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 (0.16 mi W, 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:
- 9,017 sq ft (0.21 ac)
- Assessor use:
- Single-Resid. - Improved
- Addresses on lot:
- 230 BLACKSTONE DR
Zoning & Land Use
R1 — Residential Single Family (Unincorporated Marin)
State Housing Pathways Screen (ADU & SB 9)
- ADU or junior ADULikely eligible
Zoned R1 (single-family residential): state law allows ADUs where homes are allowed.
- SB 9: two homes on the lotLikely eligible
Zoned R1, a single-family residential zone.
- SB 9: split into two lotsLikely eligible
Zoned R1, a single-family residential zone. The lot is 9,017 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
- Moderate Fire Hazard Severity Zone (Local Responsibility Area) (about 17% 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: $1,148,000 – $1,460,000 · 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)0.16 mi W
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).
- New commercial building at 200 Marinwood Ave (Applied)0.25 mi S
Active in "Applied" for 3.9 yr (first record Dec 14, 2022) with no new permit activity recorded in 3.9 yr. High-impact scale ($35,000,000 declared valuation across 2 permits).
- Accessory dwelling unit at 2558 Heatherstone Dr (Applied)0.22 mi SW
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).
- New garage / accessory structure (180842) (Issued)On this parcel
Issued after 13 mo (2.5× the 164d median) — above the 75th percentile for new garage / accessory structure permits in Unincorporated Marin (median 164d, 75th pct 294d, n=356).
Entity-resolved builders & contractors in ½ mile: Owner Builder (1 on parcel, 36 in ½ mi · Remodel / interior alteration); Home Depot The (1 on parcel, 3 in ½ mi · Remodel / interior alteration); Pac Solar (1 on parcel, 1 in ½ mi · Solar / battery storage); Aldo Sonin (1 on parcel, 1 in ½ mi · Electrical / panel); Owner (22 in ½ mi · Remodel / interior alteration).
Permit & Project History on This Parcel (4 permits, 0 grouped projects)
| Record # | Category | Status | Applied / Issued | Valuation | Description |
|---|---|---|---|---|---|
| 180842 | New garage / accessory structure | Issued | Iss. Jan 5, 2026 | $40,000 | Legalize Workshop & Storage Building; (N) Hinged Door - B W O P |
| B33393 | Solar / battery storage | Issued | Iss. Apr 12, 2023 | $19,000 | 13.2kW PV solar system with 19.9kWh battery system |
| B20694 | Electrical / panel | Issued | Iss. Jan 2, 2020 | $250 | Upgrading service from the original 100A service installed back in 1955 to now support modern appliances such as modern … |
| 148037 | Windows / doors / siding | Issued | Iss. Jul 16, 2015 | $2,920 | Repl Patio Door Size For Size - Must Meet W U I Requirements (Refund Prepared 7/3/16)***Withdrawn |