333 Lowell Ave
Mill Valley 94941 · Tamalpais · Unincorporated Marin · Coordinates: 37.88217, -122.53148
Executive Verdict · Public-Records Synthesis
Zoned R1-B1 in Unincorporated Marin with likely ADU & SB 9 infill eligibility and zero mapped flood, fire, or fault hazard overlaps; benchmark value $2,043,000 ($1,798,000–$2,288,000).
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 5,140 sq ft lot. Local precedent is active with 12 ADU permits within ¼ mile over the last 36 months.
Source: Unincorporated Marin zoning · CA Gov. Code 66314 & 65852.21
- ✓ 4 documented municipal building permits 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)
- ✓ 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)
- ! 6 slow or stalled nearby projects within ½ mile
Closest lead: New home at 217 Cleveland Ave (0.27 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)
- ! Year 1 Prop 13 tax reset (~$23,945/yr at $2,043,000)
Sale triggers reassessment to 1.00% base + ~0.15% voter debt (~$1,995/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:
- 5,140 sq ft (0.12 ac)
- Assessor use:
- Single-Resid. - Improved
- Addresses on lot:
- 333 LOWELL AVE
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 5,140 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: $1,798,000 – $2,288,000 · 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 217 Cleveland Ave (Issued)0.27 mi NE
Active in "Issued" for 9.7 yr (first record Feb 21, 2017) with no new permit activity recorded in 2.3 yr. High-impact scale (1 housing unit, $875,000 declared valuation across 1 permit).
- Accessory dwelling unit at 403 Marin Ave (adu 403a) (Issued)0.37 mi SW
Active in "Issued" for 2.9 yr (first record Dec 21, 2023) with no new permit activity recorded in 19 mo. High-impact scale (1 housing unit, $1,000,000 declared valuation across 1 permit).
- Accessory dwelling unit at 131 Yale Ave A (Issued)0.42 mi N
Active in "Issued" for 4.8 yr (first record Jan 19, 2022) with no new permit activity recorded in 3.4 yr. High-impact scale (1 housing unit, $1,000,000 declared valuation across 1 permit).
- New commercial building at 100 Harvard Ave (Issued)0.44 mi N
Active in "Issued" for 23 mo (first record Dec 26, 2024) with no new permit activity recorded in 18 mo. High-impact scale ($6,500,000 declared valuation across 1 permit).
Entity-resolved builders & contractors in ½ mile: Danny Gallagher And (1 on parcel, 1 in ½ mi · Plumbing / water heater / sewer); Bellows Plumbing Heating And Air (1 on parcel, 1 in ½ mi · HVAC / heat pump); Strom Electric (1 on parcel, 1 in ½ mi · Electrical / panel); All Marin Electric (1 on parcel, 1 in ½ mi · EV charger); Owner Builder (118 in ½ mi · Remodel / interior alteration).
Permit & Project History on This Parcel (4 permits, 0 grouped projects)
| Record # | Category | Status | Applied / Issued | Valuation | Description |
|---|---|---|---|---|---|
| B47132 | EV charger | Issued | Iss. Jun 12, 2026 | $825 | EV Charging Station; With Electronic Inspection |
| B45169 | Plumbing / water heater / sewer | Issued | Iss. Dec 29, 2025 | $94,000 | PERMIT 1 UPSTAIRS BATHROOM: (N) TILE FLOOR TO REPLACE (E); (N) VANITY AND (N) PLUMBING FIXTURES TO REPLACE (E); (N) VANI… |
| B30819 | HVAC / heat pump | Issued | Iss. Aug 23, 2022 | $13,000 | Replace existing 80% FAU and install Mitsubishi Heat Pump with ducted Air Handler — Mechanical Appliance |
| 141685 | Electrical / panel | Issued | Iss. Feb 25, 2014 | $2,500 | Relocate Electrical Sub Panel; Install New Branch Circuit For Hot Water Heater |