378 Lowell Ave
Mill Valley 94941 · Tamalpais · Unincorporated Marin · Coordinates: 37.88346, -122.53203
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 $2,310,000 ($2,033,000–$2,587,000).
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 20,822 sq ft lot. Local precedent is active with 10 ADU permits within ¼ mile over the last 36 months.
Source: Unincorporated Marin zoning · CA Gov. Code 66314 & 65852.21
- ✓ Documented permitted upgrades (+$36,000 contributory est.)
Public building records show issued construction/renovation work on this parcel (7 total permits, latest Sep 16, 2022).
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)
- ! Delayed or open permit activity on this parcel
General repair (90316): Pending in review for 4.2 yr (18.3× the 83d median) — slower than 90% of general repair permits in Unincorporated Marin (median 83d, 90th pct 328d, n=693).
Source: County of Marin Community Development Agency, Building Permits (unincorporated Marin) (review-time benchmark)
- ! 3 slow or stalled nearby projects within ½ mile
Closest lead: New home at 560 Alta Way (0.49 mi W, 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 (~$27,015/yr at $2,310,000)
Sale triggers reassessment to 1.00% base + ~0.15% voter debt (~$2,251/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:
- 20,822 sq ft (0.48 ac)
- Assessor use:
- Single-Resid. - Improved
- Addresses on lot:
- 378 LOWELL AVE
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 20,822 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 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: $2,033,000 – $2,587,000 · 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
- New home at 560 Alta Way (Applied)0.49 mi W
In "Applied" for 3.3 yr (since Aug 10, 2023), exceeding the 253d median and 686d 90th percentile for new single-family home permits in Unincorporated Marin (n=121). High-impact scale (1 housing unit, $975,000 declared valuation across 1 permit).
- General repair (90316) (Applied)On this parcel
Pending in review for 4.2 yr (18.3× the 83d median) — slower than 90% of general repair permits in Unincorporated Marin (median 83d, 90th pct 328d, n=693).
- Plumbing / water heater / sewer (166590) (Issued)On this parcel
Issued after 2 mo — slower than 90% of plumbing / water heater / sewer permits in Unincorporated Marin (median 0d, 90th pct 0d, n=2,211).
- New garage / accessory structure (166332) (Issued)On this parcel
Issued after 22 mo (4.1× the 164d median) — slower than 90% of new garage / accessory structure permits in Unincorporated Marin (median 164d, 90th pct 485d, n=356).
Entity-resolved builders & contractors in ½ mile: Hendrickson Pools (1 on parcel, 3 in ½ mi · Pool / spa); Barker Odonoghue Master Builder (1 on parcel, 1 in ½ mi · New garage / accessory structure); Divine Electric (1 on parcel, 1 in ½ mi · Plumbing / water heater / sewer); Rikety Ventures (1 on parcel, 1 in ½ mi · HVAC / heat pump); California Delta Mechanical (1 on parcel, 1 in ½ mi · HVAC / heat pump).
Permit & Project History on This Parcel (7 permits, 0 grouped projects)
| Record # | Category | Status | Applied / Issued | Valuation | Description |
|---|---|---|---|---|---|
| 90316 | General repair | Applied | App. Sep 16, 2022 | $41,500 | Retaining Wall @ Road/Driveway |
| 169628 | Pool / spa | Issued | Iss. Oct 14, 2021 | $148,350 | Pool & Auto Cover |
| B26971 | HVAC / heat pump | Issued | Iss. Sep 10, 2021 | $30,000 | 32 Panel - 12.8 kW Residential Rooftop Solar Install w/(N)Solar Ready 200A Main Service Panel & (N)125A Solar Load Cente… |
| 167025 | New garage / accessory structure | Issued | Iss. Feb 1, 2021 | $110,000 | Det Garage W/Deck On Top T.D. 6/8/20 |
| 166590 | Plumbing / water heater / sewer | Issued | Iss. Dec 16, 2020 |