23 Hearthstone Ct
San Rafael 94903 · Marinwood · Unincorporated Marin · Coordinates: 38.04030, -122.54580
Executive Verdict · Public-Records Synthesis
Zoned R1 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 $1,311,000 ($1,154,000–$1,468,000).
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 8,538 sq ft lot.
Source: Unincorporated Marin zoning · CA Gov. Code 66314 & 65852.21
- ✓ Documented permitted upgrades (+$20,900 contributory est.)
Public building records show issued construction/renovation work on this parcel (3 total permits, latest May 7, 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)
- ! 6 slow or stalled nearby projects within ½ mile
Closest lead: 125 new homes (0.27 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 (~$15,527/yr at $1,311,000)
Sale triggers reassessment to 1.00% base + ~0.15% voter debt (~$1,294/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:
- 8,538 sq ft (0.20 ac)
- Assessor use:
- Single-Resid. - Improved
- Addresses on lot:
- 23 HEARTHSTONE CT
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 8,538 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: $1,154,000 – $1,468,000 · 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)0.27 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)0.34 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)0.31 mi SE
Active in "Issued" for 19 mo (first record Apr 23, 2025) with no new permit activity recorded in 14 mo.
- Demolition at 249 Johnstone Dr (Issued)0.43 mi E
Active in "Issued" for 8.7 yr (first record Mar 15, 2018) with no new permit activity recorded in 8.6 yr.
Entity-resolved builders & contractors in ½ mile: Owner (1 on parcel, 22 in ½ mi · Remodel / interior alteration); Equinox Roofing Solutions (1 on parcel, 1 in ½ mi · Roof replacement); Bellows Plumbing Heating And Air (1 on parcel, 1 in ½ mi · HVAC / heat pump); Owner Builder (40 in ½ mi · Remodel / interior alteration); Kl Construction (3 in ½ mi · Addition (adds square footage)).
Permit & Project History on This Parcel (3 permits, 0 grouped projects)
| Record # | Category | Status | Applied / Issued | Valuation | Description |
|---|---|---|---|---|---|
| B37958 | Roof replacement | Issued | Iss. May 7, 2024 | $25,000 | re-roof, tear-off of 28 SQ Install Owens Corning TruDefinition® DURATION® COOL PLUS SHINGLES & 4 SQ Install 3-ply, APP m… |
| 166305 | Remodel / interior alteration | Issued | Iss. Nov 18, 2020 | $50,000 | Remodel Kitchen & 2 Baths, Incl Replacing Kitchen Window - Express |
| B23337 | HVAC / heat pump | Issued | Iss. Aug 24, 2020 | $10,500 | Replace existing AC in same location at the back of the property. Like for like. Relocate existing FAU from hallway clos… |