425 Wellesley Ave
Mill Valley 94941 · Tamalpais · Unincorporated Marin · Coordinates: 37.88225, -122.53663
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 $2,319,000 ($2,041,000–$2,597,000).
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 30,100 sq ft lot. Local precedent is active with 4 ADU permits within ¼ mile over the last 36 months.
Source: Unincorporated Marin zoning · CA Gov. Code 66314 & 65852.21
- ✓ Documented permitted upgrades (+$14,778 contributory est.)
Public building records show issued construction/renovation work on this parcel (8 total permits, latest Feb 3, 2026).
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 560 Alta Way (0.31 mi NW, 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 (~$27,119/yr at $2,319,000)
Sale triggers reassessment to 1.00% base + ~0.15% voter debt (~$2,260/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:
- 30,100 sq ft (0.69 ac)
- Assessor use:
- Single-Resid. - Improved
- Addresses on lot:
- 425 WELLESLEY 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 30,100 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: $2,041,000 – $2,597,000 · 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)0.31 mi NW
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).
- Accessory dwelling unit at 403 Marin Ave (adu 403a) (Issued)0.3 mi S
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).
- New home at 731 Bay Rd (Issued)0.33 mi SW
Active in "Issued" for 18 mo (first record May 12, 2025) with no new permit activity recorded in 15 mo. High-impact scale (1 housing unit, $955,000 declared valuation across 1 permit).
- New home at 469 W Live Oak Dr (aka 461) (Issued)0.44 mi SW
Active in "Issued" for 6.1 yr (first record Oct 22, 2020) with no new permit activity recorded in 22 mo. High-impact scale (1 housing unit, $980,000 declared valuation across 1 permit).
Entity-resolved builders & contractors in ½ mile: Scopazzi Construction (2 on parcel, 2 in ½ mi · General repair); Ed Electric Group (2 on parcel, 2 in ½ mi · Electrical / panel); Fitzpatricks Heating (2 on parcel, 2 in ½ mi · HVAC / heat pump); Simply Solar (1 on parcel, 1 in ½ mi · Solar / battery storage); Fast Water Heater (1 on parcel, 1 in ½ mi · Plumbing / water heater / sewer).
Permit & Project History on This Parcel (8 permits, 0 grouped projects)
| Record # | Category | Status | Applied / Issued | Valuation | Description |
|---|---|---|---|---|---|
| B45735 | Electrical / panel | Issued | Iss. Feb 3, 2026 | $5,443 | New Circuits / Outlets |
| B34144 | Plumbing / water heater / sewer | Issued | Iss. Jun 2, 2023 | $4,195 | Remove/replace electric water heater. — Replace Plumbing Fixtures(s) |
| B33952 | EV charger | Issued | Iss. May 19, 2023 | $9,498 | Service upgrade and panel replacement 100-200 amps. solar ready panel. Install EV charger. Replace and relocate Sub pane… |
| B31019 | Solar / battery storage | Issued | Iss. Sep 13, 2022 | $39,094 | RESIDENTIAL PV SOLAR, FLUSH ROOF MOUNT, GRID TIED. |
| B28346 | HVAC / heat pump | Issued | Iss. Jan 13, 2022 |