51 Castle Rock Ave
Woodacre 94973 · Woodacre · Unincorporated Marin · Coordinates: 38.00567, -122.63386
Executive Verdict · Public-Records Synthesis
Zoned R1-B2-SGV in Unincorporated Marin with likely ADU & SB 9 infill eligibility and mapped CAL FIRE high fire hazard severity zone (state responsibility area) due diligence; benchmark value $1,203,000 ($1,059,000–$1,347,000).
Upsides & Opportunities
- ✓ ADU & SB 9 infill pathways screen as likely eligible
Zoned R1-B2-SGV supports ministerial ADU/JADU review plus SB 9 both two-unit development and ministerial urban lot split on a 27,138 sq ft lot.
Source: Unincorporated Marin zoning · CA Gov. Code 66314 & 65852.21
- ✓ 2 documented municipal building permits on file
On-parcel permit history is indexed through Sep 26, 2023, 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
- ! 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 (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)
- ! Delayed or open permit activity on this parcel
New home: In "Entitled" for 5.3 yr (since Jul 12, 2021), exceeding the 253d median and 686d 90th percentile for new single-family home permits in Unincorporated Marin (n=121).
Source: County of Marin Community Development Agency, Building Permits (unincorporated Marin) (review-time benchmark)
- ! 4 slow or stalled nearby projects within ½ mile
Closest lead: New home at 80 Fire Rd (0.31 mi NE, 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)
Parcel & Assessor
- Lot size:
- 27,138 sq ft (0.62 ac)
- Assessor use:
- Single-Resid. - Improved
- Addresses on lot:
- 51 CASTLE ROCK AVE
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 lotLikely eligible
Zoned R1-B2-SGV, a single-family residential zone.
- SB 9: split into two lotsLikely eligible
Zoned R1-B2-SGV, a single-family residential zone. The lot is 27,138 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 (State Responsibility Area) (all of the lot, map Apr 1, 2024)
- FEMA National Flood Hazard Layer
- Zone X: minimal flood hazard (all 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: $1,059,000 – $1,347,000 · Status: Off market
HUD Small Area FMR (ZIP 94973) · FY 2026
Studio $2,080 · 1BR $2,510 · 2BR $3,020 · 3BR $3,860 · 4BR $4,000
Developments Deserving Closer Investigation & Active Area Builders
- New home (Entitled)On this parcel
In "Entitled" for 5.3 yr (since Jul 12, 2021), exceeding the 253d median and 686d 90th percentile for new single-family home permits in Unincorporated Marin (n=121).
- New home at 80 Fire Rd (Issued)0.31 mi NE
Active in "Issued" for 4.1 yr (first record Sep 28, 2022) with no new permit activity recorded in 3.5 yr. High-impact scale (1 housing unit, $2,000,000 declared valuation across 1 permit).
- New home at 15 Edgewood Dr (Applied)0.34 mi SW
In "Applied" for 6.1 yr (since Oct 22, 2020), exceeding the 253d median and 686d 90th percentile for new single-family home permits in Unincorporated Marin (n=121).
- New home at 10 Holly Ln (Applied)0.4 mi W
Active in "Applied" for 14 mo (first record Sep 17, 2025) with no new permit activity recorded in 14 mo.
Entity-resolved builders & contractors in ½ mile: Ed Electric Group (1 on parcel, 1 in ½ mi · Electrical / panel); Owner Builder (9 in ½ mi · New garage / accessory structure); Owner (5 in ½ mi · Demolition); Peters Design Build (1 in ½ mi · New single-family home); Crafted Earth (1 in ½ mi · Remodel / interior alteration).
Permit & Project History on This Parcel (2 permits, 1 grouped projects)
| Record # | Category | Status | Applied / Issued | Valuation | Description |
|---|---|---|---|---|---|
| B35536 | Electrical / panel | Issued | Iss. Sep 26, 2023 | $6,250 | Service upgrade Overhead. 100-200 amps.New service system 200 amps solar ready — Service Upgrade |
| 173957 | New garage / accessory structure | Issued | Iss. May 4, 2023 | $75,000 | Demo [E] Carport & Construct [N] Det Garage T.D. 10-27-22 |
State HCD Housing Element APR records on this parcel: 1 entry (report years 2021).