807 Spring Dr
Mill Valley 94941 · Tamalpais · Unincorporated Marin · Coordinates: 37.87572, -122.54365
Executive Verdict · Public-Records Synthesis
Zoned R1-B1 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 $2,096,000 ($1,844,000–$2,348,000).
Upsides & Opportunities
- ✓ ADU & SB 9 infill pathways screen as likely eligible
Zoned R1-B1 supports ministerial ADU/JADU review plus SB 9 both two-unit development and ministerial urban lot split on a 6,534 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 (+$13,640 contributory est.)
Public building records show issued construction/renovation work on this parcel (7 total permits, latest May 9, 2023).
Source: County of Marin Community Development Agency, Building Permits (unincorporated Marin) (parcel APN)
- ✓ Above-average reinvestment in Tamalpais
50 substantial renovation & housing permits over 24 months (20.5 per 1,000 parcels vs. 16.4 citywide baseline) (#3 of 22 neighborhoods).
Source: County of Marin Community Development Agency, Building Permits (unincorporated Marin) (Tamalpais)
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)
- ! 6 slow or stalled nearby projects within ½ mile
Closest lead: Accessory dwelling unit at 875 Marin Dr (480 ft SW, applied). 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 (~$24,554/yr at $2,096,000)
Sale triggers reassessment to 1.00% base + ~0.15% voter debt (~$2,046/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:
- 6,534 sq ft (0.15 ac)
- Assessor use:
- Single-Resid. - Improved
- Addresses on lot:
- 807 SPRING DR
Zoning & Land Use
R1-B1 — Residential Single Family (Unincorporated Marin)
State Housing Pathways Screen (ADU & SB 9)
- ADU or junior ADULikely eligible
Zoned R1-B1 (single-family residential): state law allows ADUs where homes are allowed.
- SB 9: two homes on the lotLikely eligible
Zoned R1-B1, a single-family residential zone.
- SB 9: split into two lotsLikely eligible
Zoned R1-B1, a single-family residential zone. The lot is 6,534 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 06041C0468F, effective March 16, 2016
- CGS Alquist-Priolo Earthquake Fault Zone
- Not in an Alquist-Priolo Earthquake Fault Zone
Surrounding Rent & Value Benchmarks (Public Records)
Range: $1,844,000 – $2,348,000 · Status: Off market
HUD Small Area FMR (ZIP 94941) · FY 2026
Studio $2,730 · 1BR $3,270 · 2BR $3,960 · 3BR $5,060 · 4BR $5,240
Developments Deserving Closer Investigation & Active Area Builders
- Accessory dwelling unit at 875 Marin Dr (Applied)480 ft SW
In "Applied" for 2.6 yr (since Apr 11, 2024), exceeding the 253d median and 686d 90th percentile for new single-family home permits in Unincorporated Marin (n=121). Record changed to "updated" in snapshot Nov 4, 2026.
- New home at 808 Spring Dr (Issued)140 ft NE
Active in "Issued" for 4.9 yr (first record Dec 13, 2021) with no new permit activity recorded in 4.7 yr. High-impact scale (1 housing unit, $850,000 declared valuation across 1 permit).
- New home at 812 Spring Dr (Issued)140 ft N
Active in "Issued" for 4.1 yr (first record Sep 19, 2022) with no new permit activity recorded in 3.3 yr. High-impact scale (1 housing unit, $1,006,000 declared valuation across 1 permit).
- New home at 746 Alta Vista Rd (Issued)520 ft NE
Active in "Issued" for 3.3 yr (first record Jul 19, 2023) with no new permit activity recorded in 2.3 yr. High-impact scale (1 housing unit, $1,183,700 declared valuation across 2 permits).
Entity-resolved builders & contractors in ½ mile: De Mello Roofing (1 on parcel, 1 in ½ mi · Roof replacement); Structural Integrity (1 on parcel, 1 in ½ mi · Remodel / interior alteration); Ernest Ongaro And Sons (1 on parcel, 1 in ½ mi · HVAC / heat pump); Solarcity Dba Tesla Energy (1 on parcel, 1 in ½ mi · Solar / battery storage); Berkeley Electric (1 on parcel, 1 in ½ mi · Electrical / panel).
Permit & Project History on This Parcel (7 permits, 0 grouped projects)
| Record # | Category | Status | Applied / Issued | Valuation | Description |
|---|---|---|---|---|---|
| B33801 | Solar / battery storage | Issued | Iss. May 9, 2023 | $600 | Remove and reinstall roof mount solar panels at 2.53 kW |
| B33263 | Roof replacement | Issued | Iss. Apr 3, 2023 | $20,810 | ENTIRE HOUSE TEAR OFF EXISTING BUILT-UP ROOF INSTALL NEW BUILT-UP ROOF CLASS A — ReRoofing |
| B20966 | Electrical / panel | Issued | Iss. Jan 31, 2020 | $1,200 | Install manual transfer switch kit (110 volt/4-circuit) at garage interior. No change to main panel or sub panels. No ad… |
| B20182 | HVAC / heat pump | Issued | Iss. Oct 22, 2019 | $8,000 | Replace failed furnace and ducting with new furnace and ducting- 11 runs of R6 wireflex — Replace Ductwork, Replace Mech… |
| 152174 | Remodel / interior alteration |