287 Blackstone Dr
San Rafael 94903 · Marinwood · Unincorporated Marin · Coordinates: 38.03795, -122.54111
Executive Verdict · Public-Records Synthesis
Zoned R1 in Unincorporated Marin with likely ADU & SB 9 infill eligibility and zero mapped flood, fire, or fault hazard overlaps; benchmark value $1,531,000 ($1,347,000–$1,715,000).
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 7,797 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 (+$249,600 contributory est.)
Public building records show issued construction/renovation work on this parcel (3 total permits, latest Sep 5, 2025).
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)
- ! Delayed or open permit activity on this parcel
Accessory dwelling unit at 287 Blackstone Dr: Active in "Issued" for 19 mo (first record Apr 23, 2025) with no new permit activity recorded in 14 mo.
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 (180 ft NW, 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 (~$18,057/yr at $1,531,000)
Sale triggers reassessment to 1.00% base + ~0.15% voter debt (~$1,505/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:
- 7,797 sq ft (0.18 ac)
- Assessor use:
- Single-Resid. - Improved
- Addresses on lot:
- 287 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 7,797 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
- Not in a State-mapped fire hazard severity zone
- 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: $1,347,000 – $1,715,000 · 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)180 ft NW
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 287 Blackstone Dr (Issued)On this parcel
Active in "Issued" for 19 mo (first record Apr 23, 2025) with no new permit activity recorded in 14 mo.
- New commercial building at 200 Marinwood Ave (Applied)0.27 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)0.14 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).
Entity-resolved builders & contractors in ½ mile: Filshie Enterprises (1 on parcel, 1 in ½ mi · Accessory dwelling unit (new or conversion)); Allen Heating And Sheet Metal (1 on parcel, 1 in ½ mi · HVAC / heat pump); Integrity Electric (1 on parcel, 1 in ½ mi · Electrical / panel); Owner Builder (41 in ½ mi · Remodel / interior alteration); Owner (23 in ½ mi · Remodel / interior alteration).
Permit & Project History on This Parcel (3 permits, 1 grouped projects)
| Record # | Category | Status | Applied / Issued | Valuation | Description |
|---|---|---|---|---|---|
| 179994 | Accessory dwelling unit (new or conversion) | Issued | Iss. Sep 5, 2025 | $500,000 | Whole House Remodel; Kitchen Addition; (N) Attached Rear Ground Flr J A D U; Covered Entry Porch |
| 149500 | Electrical / panel | Issued | Iss. Oct 20, 2015 | $6,300 | Service Upgrade To 200 Amp, Circuit For A/C System By Others, Can Lights In Lvg Rm |
| 149349 | HVAC / heat pump | Issued | Iss. Oct 12, 2015 | $10,864 | Rplc Heating And A/C***Expired |
State HCD Housing Element APR records on this parcel: 1 entry (report years 2025).