403 Wellesley Ct
Mill Valley 94941 · Tamalpais · Unincorporated Marin · Coordinates: 37.88605, -122.53543
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 $2,259,000 ($1,988,000–$2,530,000).
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 15,943 sq ft lot. Local precedent is active with 9 ADU permits within ¼ mile over the last 36 months.
Source: Unincorporated Marin zoning · CA Gov. Code 66314 & 65852.21
- ✓ Documented permitted upgrades (+$28,918 contributory est.)
Public building records show issued construction/renovation work on this parcel (6 total permits, latest Apr 8, 2025).
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 (0.29 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 (~$26,429/yr at $2,259,000)
Sale triggers reassessment to 1.00% base + ~0.15% voter debt (~$2,202/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:
- 15,943 sq ft (0.37 ac)
- Assessor use:
- Single-Resid. - Improved
- Addresses on lot:
- 403 WELLESLEY CT
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 15,943 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: $1,988,000 – $2,530,000 · 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)0.29 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).
- New commercial building at 100 Harvard Ave (Issued)0.21 mi NE
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).
- Accessory dwelling unit at 131 Yale Ave A (Issued)0.37 mi E
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 home at 217 Cleveland Ave (Issued)0.4 mi E
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).
Entity-resolved builders & contractors in ½ mile: Lamperti Contracting And Design (1 on parcel, 6 in ½ mi · Remodel / interior alteration); American Solar (1 on parcel, 1 in ½ mi · Solar / battery storage); Charles Window And Door (1 on parcel, 1 in ½ mi · Windows / doors / siding); Fidelity Roof (1 on parcel, 1 in ½ mi · Solar / battery storage); Rapidflo (1 on parcel, 1 in ½ mi · HVAC / heat pump).
Permit & Project History on This Parcel (6 permits, 0 grouped projects)
| Record # | Category | Status | Applied / Issued | Valuation | Description |
|---|---|---|---|---|---|
| B41939 | HVAC / heat pump | Issued | Iss. Apr 8, 2025 | $10,471 | Replace gas furnace in crawlspace with new 96% 2 stage 60k btu upflow furnace. Like for like. — Replace Mechanical Appli… |
| 166550 | Solar / battery storage | Issued | Iss. Dec 14, 2020 | $24,000 | 6.6kw Rooftop Photovoltaic |
| B23997 | Electrical / panel | Issued | Iss. Oct 28, 2020 | $3,800 | Electrical service upgrade. Install new main panel. — Service Upgrade |
| 165969 | Remodel / interior alteration | Issued | Iss. Oct 13, 2020 | $35,000 | Rmdl Master Bath - Express |
| B23714 | Solar / battery storage | Issued | Iss. Oct 1, 2020 |