25 Castro St
Forest Knolls 94933 · Forest Knolls · Unincorporated Marin · Coordinates: 38.01480, -122.69073
Executive Verdict · Public-Records Synthesis
Zoned R1-B2-SGV in Unincorporated Marin with likely ministerial ADU eligibility and mapped FEMA A flood / CAL FIRE high fire hazard severity zone (state responsibility area) due diligence; benchmark value $938,000 ($825,000–$1,051,000).
Upsides & Opportunities
- ✓ Ministerial ADU / JADU pathway likely eligible
Zone R1-B2-SGV allows residential use qualifying for ministerial ADU review under state law (1 ADU permit permitted within ¼ mile in 36 months).
Source: Unincorporated Marin zoning · CA Gov. Code 66314
- ✓ 1 documented municipal building permit on file
On-parcel permit history is indexed through Jun 12, 2026, letting you verify roof, HVAC, electrical, or structural work against seller disclosures.
Source: County of Marin Community Development Agency, Building Permits (unincorporated Marin) (parcel APN)
Watchouts & Due Diligence
- ! FEMA Special Flood Hazard Area (A, about 33% of the lot of lot)
Zone A: 1% annual chance flood (Special Flood Hazard Area) overlaps this parcel. Expect mandatory flood insurance for federally backed loans and floodplain elevation/mitigation rules for new units or SB 9 applications.
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)
- ! 6 slow or stalled nearby projects within ½ mile
Closest lead: Demolition at 6956 Sir Francis Drake Blvd (340 ft NW, issued). 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 (~$11,237/yr at $938,000)
Sale triggers reassessment to 1.00% base + ~0.15% voter debt (~$936/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:
- 12,327 sq ft (0.28 ac)
- Assessor use:
- Single-Resid. - Improved
- Addresses on lot:
- 25 CASTRO ST
Zoning & Land Use
R1-B2-SGV — Residential Single Family (Unincorporated Marin)
State Housing Pathways Screen (ADU & SB 9)
- ADU or junior ADULikely eligible
Zoned R1-B2-SGV (single-family residential): state law allows ADUs where homes are allowed.
- SB 9: two homes on the lotPossible, with conditions
Zoned R1-B2-SGV, a single-family residential zone. FEMA Special Flood Hazard Area (Zone A) covers about 33% of the lot: the project must meet the National Flood Insurance Program floodplain standards, or the lot needs a map revision.
- SB 9: split into two lotsPossible, with conditions
Zoned R1-B2-SGV, a single-family residential zone. The lot is 12,327 sq ft by the assessor, room for two lots of at least 1,200 sq ft, each at least 40% of the original. FEMA Special Flood Hazard Area (Zone A) covers about 33% of the lot: the project must meet the National Flood Insurance Program floodplain standards, or the lot needs a map revision.
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 A: 1% annual chance flood (Special Flood Hazard Area) (about 33% of the lot); Zone X: minimal flood hazard (about 67% of the lot) · FIRM panel 06041C0275D, 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: $825,000 – $1,051,000 · Status: Off market
HUD Small Area FMR (ZIP 94933) · FY 2026
Studio $2,870 · 1BR $3,440 · 2BR $4,160 · 3BR $5,310 · 4BR $5,510
Developments Deserving Closer Investigation & Active Area Builders
- Demolition at 6956 Sir Francis Drake Blvd (Issued)340 ft NW
Active in "Issued" for 2.8 yr (first record Jan 10, 2024) with no new permit activity recorded in 2.7 yr.
- Accessory dwelling unit at 8 Morelos Ave (Issued)370 ft SW
Active in "Issued" for 6.1 yr (first record Oct 8, 2020) with no new permit activity recorded in 6.1 yr.
- Demolition at 2 Juarez Ave (Issued)0.11 mi E
Active in "Issued" for 9.9 yr (first record Dec 28, 2016) with no new permit activity recorded in 8.9 yr.
- New home at 42 Arroyo Rd (Issued)0.15 mi NW
Active in "Issued" for 12.3 yr (first record Aug 11, 2014) with no new permit activity recorded in 11.8 yr.
Entity-resolved builders & contractors in ½ mile: Rooflow (1 on parcel, 1 in ½ mi · Roof replacement); Owner Builder (10 in ½ mi · Accessory dwelling unit (new or conversion)); Owner (9 in ½ mi · New single-family home); Zia Designs (2 in ½ mi · Demolition); Rebuilding Together East Bay Network (1 in ½ mi · Accessory dwelling unit (new or conversion)).
Permit & Project History on This Parcel (1 permits, 0 grouped projects)
| Record # | Category | Status | Applied / Issued | Valuation | Description |
|---|---|---|---|---|---|
| B47136 | Roof replacement | Issued | Iss. Jun 12, 2026 | $9,800 | ReRoofing; With Electronic Inspection |