155 Mark Twain Ave
San Rafael 94903 · Santa Venetia · Unincorporated Marin · Coordinates: 38.00319, -122.52886
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 $1,213,000 ($1,067,000–$1,359,000).
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 8,015 sq ft lot. Local precedent is active with 1 ADU permit within ¼ mile over the last 36 months.
Source: Unincorporated Marin zoning · CA Gov. Code 66314 & 65852.21
- ✓ Documented permitted upgrades (+$18,746 contributory est.)
Public building records show issued construction/renovation work on this parcel (4 total permits, latest Jan 29, 2025).
Source: County of Marin Community Development Agency, Building Permits (unincorporated Marin) (parcel APN)
Watchouts & Due Diligence
- ! Mapped flood awareness zone (Zone X: 0.2% annual chance flood hazard (shaded X))
about 98% of the lot of the parcel intersects Zone X: 0.2% annual chance flood hazard (shaded X). 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 commercial building at 10 Ave Of The Flags (0.25 mi W, 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 (~$14,400/yr at $1,213,000)
Sale triggers reassessment to 1.00% base + ~0.15% voter debt (~$1,200/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:
- 8,015 sq ft (0.18 ac)
- Assessor use:
- Single-Resid. - Improved
- Addresses on lot:
- 155 MARK TWAIN 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 8,015 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: 0.2% annual chance flood hazard (shaded X) (about 98% of the lot) · FIRM panel 06041C0294E, 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: $1,067,000 – $1,359,000 · Status: Off market
HUD Small Area FMR (ZIP 94903) · FY 2026
Studio $2,880 · 1BR $3,450 · 2BR $4,180 · 3BR $5,340 · 4BR $5,530
Developments Deserving Closer Investigation & Active Area Builders
- New commercial building at 10 Ave Of The Flags (Issued)0.25 mi W
Active in "Issued" for 5.6 yr (first record Mar 26, 2021) with no new permit activity recorded in 5.5 yr. High-impact scale ($2,000,000 declared valuation across 1 permit).
- New commercial building at 170 N San Pedro Rd (Issued)0.39 mi SE
Active in "Issued" for 5 yr (first record Dec 1, 2021) with no new permit activity recorded in 4.4 yr. High-impact scale ($18,000,000 declared valuation across 1 permit).
- Accessory dwelling unit at 15 Roosevelt Ave (Applied)0.27 mi SE
In "Applied" for 4.3 yr (since Jul 13, 2022), exceeding the 253d median and 686d 90th percentile for new single-family home permits in Unincorporated Marin (n=121).
- Demolition at 13 Edward Ave (Applied)0.34 mi E
In "Applied" for 3.8 yr (since Jan 23, 2023), exceeding the 55d median and 261d 90th percentile for demolition permits in Unincorporated Marin (n=130).
Entity-resolved builders & contractors in ½ mile: Sunrun Installation Services (1 on parcel, 1 in ½ mi · Solar / battery storage); 3 D Remodeling (1 on parcel, 1 in ½ mi · Remodel / interior alteration); John Owens Services (1 on parcel, 1 in ½ mi · HVAC / heat pump); Fwh Acquisition (1 on parcel, 1 in ½ mi · Plumbing / water heater / sewer); Owner Builder (35 in ½ mi · Remodel / interior alteration).
Permit & Project History on This Parcel (4 permits, 0 grouped projects)
| Record # | Category | Status | Applied / Issued | Valuation | Description |
|---|---|---|---|---|---|
| B41029 | Solar / battery storage | Issued | Iss. Jan 29, 2025 | $23,022 | PV SOLAR 7.38KW DC, 11.5KW AC, (18) MODULES, (1) 13.5KWh ESS, Main Panel Replacement |
| B24653 | HVAC / heat pump | Issued | Iss. Jan 20, 2021 | $7,434 | Replace furnace — Replace Mechanical Appliance |
| 166756 | Remodel / interior alteration | Issued | Iss. Jan 5, 2021 | $20,000 | Kitchen Remodel |
| B23565 | Plumbing / water heater / sewer | Issued | Iss. Sep 15, 2020 | $1,694 | Remove/replace gas water heater — Replace Plumbing Fixtures(s) |